## Mcrp 3-17.7A Preface

dardization Program, Fortification for Parked Aircraft.

Field Manual (FM) 5-430 is intended for use as a training guide and reference text for engineer personnel responsible for planning, designing, and constructing roads, airfields, and heliports in the theater of operations
(TO).

- North Atlantic Treaty Organization
(NATO) Standardization Agreement (STANAG) 3158 Airfield Marking and
Lighting (AML) (Edition 4), Day Marking
of Airfield Runways and Taxiways.
Z STANAG 2929, Airfield Damage Repair. - STANAG 3346 AML (Edition 4), Marking
and Lighting of Airfield Obstructions.
FM 5-430 is divided into two separate volumes to make it more *user-friendly.* FM 5-
430-00-1/AFPAM 32-8013, Vol 1, Road Design, encompasses Chapters 1 through 9
and Appendices A through H. FM 5-430-00- 2/AFJPAM 32-8013, Vol II, Airfield and Heliport Design, encompasses Chapters 10
through 14 and Appendices I through P.

Z STANAG 3601 Air Transport (TN) (Edition 3), Criteria for Selection and Marking of Landing Zones for Fixed Wing Transport Aircraft.
Z STANAG 3619 AML (Edition 2) (Amendment 2), Helipad Marking.
- STANAG 3652 AML (Amendment 3), Helipad Lighting, Visual Meteorological Conditions (VMC).
FM 5-430-00-l/AFPAM 32-8013, Vol 1 is a stand-alone volume for the design of TO
roads. This volume also serves as a detailed description of information common to both roads and airfields, such as site selection, survey and earthwork, clearing and grubbing, base and subbase courses, and drainage.

- STANAG 3685 AML, Airfield Portable
Marking.
This publication applies to the Air National Guard (ANG) when published in the National Guard Regulation (NGR) (AF) 0-2.

This publication, together with FM 5-430-00-
2/AFJPAM 32-8013, Vol H: Airfield and Heliport Design (to be published), will supersede TM 5-330/AFM 86-3, Volume II, 8 September 1968 and FM 5-165/AFP 86-13, 29
August 1975.

FM 5-430-00-2 /AFJPAM 32-8013, Vol II serves as the basis for airfield and heliport design. It discusses the complete process of airfield and heliport construction from the preliminary investigations, through design criteria, to the final project layout and construction techniques. It is not a standalone volume. FM 5-430-00-1/AFPAM 32- 8013, Vol 1 contains much of the information required to design the substructure of an airfield or a heliport.

The proponent for this publication is the US Army Engineer School (USAES). Send comments and recommendations on Department of the Army (DA) Form 2028 (Recommended Changes to Publications and Blank Forms) directly to
The material in this manual applies to all levels of engineer involvement in the TO.

The manual is intended to be used by United States (US) Army Corps of Engineers personnel.

The provisions of this publication are the subject of the following international agreements:
Commandant US Army Engineer School ATSE-TDM
Fort Leonard Wood, MO 65473-5000.

- Quadripartite Standardization Agreement [QSTAG) 306, American-British- Canadian-Australian Armies Stan-
Unless this publication states otherwise, masculine nouns and pronouns do not refer exclusively to men.

Road Construction Basic Planning Considerations in the Theater of Operations Engineering Study General Information Airfield Construction
1

## General Information

Army engineers plan, design, and construct airfields, heliports,
and roads in the TO. To ensure these facilities meet proposed
requirements, the responsible engineer officer must coordinate
closely with all appropriate ground and air commanders.
                                                            The
engineer depends on the appropriate commanders for informa-
tion on the weight and traffic frequency of using aircraft, facility
life, geographic boundaries governing site selection, and the
time available for construction as dictated by the operation plan.

Detailed planning, reconnaissance, and site investigations are
often limited by lack of time and by the tactical situation. How-
even when time and security permit, the engineer should conduct
normal ground reconnaissance and on-site investigations. If
this is not possible, the engineer should obtain photographs of
the area.

## Basic Planning Considerations In The Theater Of Operations

Army engineers should use the following guides in the TO:

- Build one of two types of structures in
the TO: initial or temporary. Initial
design life is up to six months; temporary design life is up to two years.
- Keep designs simple. Simple designs require minimum skilled labor and specialized materials.
Z Whenever possible, phase construction
to permit the early usc of the facility while further construction and improvements continue.
- Use local materials whenever possible.
This helps eliminate construction delays associated with a long communications
and logistics line.
Z Generally avoid sites with dense brush,
timberland, and rolling terrain that require heavy clearing or grading.
- Use existing facilities whenever possible. This helps avoid unnecessary construction.
Z Take care to prevent destruction of
natural drainage channels, culverts,
and roads. Repairs require time and
labor far exceeding that needed to
prevent  damage.
- Remember that safety factors in design
are drastically reduced in the TO because of time constraints and the inherent risks of war.

## Airfield Construction Army Responsibilities

The Army will provide the following troop construction support to the Air Force:
The planning and construction of Air Force bases in the TO is a joint responsibility of Army and Air Force personnel as outlined in Army Regulation (AR) 415-30/Air Force Regulation (AFR) 93-10. A summary of each service's responsibilities follows:

Z Development of engineering designs,
standard plans, and material to meet
Air Force requirements.

## Air Force Responsibilities

The Air Force provides the following support:

- Reconnaissance, survey, design, construction, or improvement of airfields,
roads, utilities, and structures.
- Emergency repair of war-damaged air
bases.
Z Rehabilitation of Air Force bases and facilities beyond the immediate emergency recovery requirements of the Air
Force.
- Force bed down of Air Force units and
weapon systems, excluding Army basedevelopment responsibilities.
Z Supply of materials and equipment to
perform Army engineering missions.
- Construction management of emergency
repair of war damage and force beddown.
Z Construction of temporary standard air
base facilities.
- Operation and maintenance of Air Force
facilities and installations.
- Crash rescue and fire suppression.
Z Repair management of war damage and
base development, including supervision of Army personnel. The Air Force base commander will set the work priorities.
- Supply of material and equipment to
perform Air Force engineering missions.
- Road and airfield construction.

## Road Construction

Engineer construction units, under the
- Construct and install signs and other appropriate Army command, have the following route-marking materials.

responsibilities:
Z Regulate traffic at locations where engi-

- Reconnoiter roads and bridges.
neer work is being performed.
Z Assist vehicles to keep traffic moving on
- Recommend traffic-control procedures.
main supply routes regardless of weather, enemy activity, or other difficulties.

## Engineering Study

After the specific requirements for roads, using certain airfields and roads.

To obtain air fields. and heliports have been these facilities quickly, an adequate determined engineers should prepare the investigation of each site and a careful facilities for use as soon as possible. In study of the design details are essential.

most cases, the he need is critical because the This is explained in greater detail in accomplishment of a mission depends on Chapter 2 of this manual.

Route and Road Reconnaissance Airfield Reconnaissance Location Factors Reconnaissance Site Selection and Reconnaissance Engineer Reconnaissance

## Site Selection And Reconnaissance

This chapter outlines the location, layout, and design of military
roads and airfields.
                       The first steps in constructing a road or
airfield are determining the best location for the facility and
formulating the essential areas and construction features.
Throughout the preconstruction phase, problems can be avoided
by a well-planned site selection.

## Factors Location

world, Where possible, use these roadnets to the fullest extent. In many cases, expansion and rehabilitation of existing facilities is adequate for mission accomplishment.

Construction of a road or airfield initially consists of providing a prepared subgrade and base course according to design criteria.

Airfield runways require more transverse areas than roads.

Although the governing criteria and dimensions for roads and airfields differ, the basic approach to their location and layout is the same. Engineers should use the factors listed below to locate and lay out all construction projects.

## Mission

or Except in highly developed areas, existing airfields are seldom adequate to handle modern, high-performance aircraft. However, with minimum rehabilitation these airfields can usually be made adequate to accommodate them. They may serve as the nucleus for larger fields that meet the requirements of high-performance aircraft.

Helicopters and light planes can often operate from existing roads, pastures, athletic fields.

## Location And Design

The most important factor in selecting a site is to ensure it will fulfill mission requirements. Lines of communication (LOC)
must be build to accomplish a specific mission in the most direct and efficient manner possible.

All location factors must be evaluated to support the mission.

## Existing Facilities

To the greatest extent possible, the location and design for a facility must provide the best response to all requirements. Alternative road and airfield plans can be evaluated, from the standpoint of total earthwork and drainage structure requirements, to reduce construction effort.

Try to construct airfields in an area that will serve existing and future requirements.

Consider the future needs of military units Use all existing facilities. The wartime missions of engineer troops arc so extensive and the demand for their services so great that new construction should be avoided.

Extensive roadnets of varying quality and capacity already exist in most areas of the and facilities, such as depots and hospitals, when locating roads. Soil type and incumbent pavement structure requirements, rock formations, and vegetation should also be considered in locating roads.

A given road segment to be constructed or improved should be considered in view of its contribution to the overall network. Similarly, an airfield should be evaluated for its ability to enhance an arifield network.

Avoid constructing facilities in areas of high water tables. Although it is possible to construct subsurface structures that will remove part of this moisture, maintaining routes through these areas presents a continual problem.

If it is impossible to avoid constructing a road or airfield in this type of terrain, the water tables must be lowered during construction to reduce the adverse effect of water on the strength of the supporting subgrade and base course.

## Soil Characteristics Geology

Before locating any lines of communication, carefully analyze the geology of the area. Sizeable quantities of rock anywhere along a construction project will cause a large removal problem, slow construction, and increase the construction effort. Engineer troop units require special equipment and training to excavate rock.

Locate all roads and airfields on terrain having the best possible subgrade soil conditions. This will decrease construction effort and result in a better facility. The subgrade should be compacted under conditions allowing it to support the design loads. Conduct a basic soils investigation prior to construction to provide data needed to ensure good construction decisions.

Refer to FM 5-410 for soils information and FM 5-530 for soil survey procedures.

## Drainage

Rock outcropping are more common in hilly terrain than in flat or rolling country.

In areas where the preliminary design indicates that cutting is required to reach final grade, take enough borings to determine the location of the rock.

Locate roads in areas that are easily drained and where drainage structures are minimized. Drainage is a more critical factor in locating airfields than roads.

Because of the wide areas involved in airfield installations, water must be diverted completely around the field or long drainage structures that are difficult to maintain must be constructed. This topic is further discussed in Chapter 6 of this manual.

identify the type of rock material for evaluation as a suitable construction aggregate.

Determine the structural orientation of the rock mass to properly design road cuts and ensure rock-slope stability. In sedimentary rocks it is best to align road cuts perpendicular to the strike.

If this is not possible, use the safe-slope ratios shown in Figure 2-1.

## Topography

Avoid the low points of valleys or other depressed areas because they are focal points for water collection. Many airfields are constructed across long, gentle slopes because of the relative ease of diverting water around the finished installation.

Avoid construction on unprotected floodplains and alluvial fans, if possible, due to the flood hazard. Alluvial terraces are often ideal locations for air fields. They offer flat expanses that are above the river floodplain and are normally protected from flooding.

Construct all roads and airfields within maximum grade specifications. The specifications depend upon the facility's construction standard. Thus, avoid excessive grades and steep hills when locating these routes.

If steep hills must be negotiated, the route should run along the side of the hill rather than going directly over it. This may result in a longer route, but it is generally more economical and avoids excessive grades.

## 2-2 Site Selection And Reconnaissance Earthwork

obtaining suitable fill material. Align runways in the direction of the prevailing wind because aircraft usually land and take off into the wind.

## Obstacle Crossings

The largest single work item during construction of LOC is earthwork operations.

Any step that simplifies earthwork operations will decrease required work and increase job efficiency. Generally, when cutting and filling on a project, earth handling is reduced by using the material excavated to construct required embankments. This balancing must be within the haul capabilities of the available equipment.

Even though earthwork should be balanced throughout a project, if the haul distance becomes excessive, it may be more practical to open a nearby borrow pit or establish spoil areas. Balancing cannot be done where the excavated material is not acceptable for usc in an embankment.

## Alignment

Whenever a route crosses a major obstacle, such as a river, a ravine, or a canal, bridges or other structures arc required.

Construction is time-consuming and requires materials that may be in short supply. Avoid these obstacles whenever possible. It will be advantageous to forego many of the other location principles to decrease the number of obstacle crossings.

Use existing structures to decrease total work requirements, This may require only the strengthening of an existing bridge or no bridging work at all. When possible, the road should not cross a particular obstacle more than once.

## Bridge Approaches

When locating rou tes, carefully evaluate construction requirements for approaches to obstacles. Construction of approaches over marshes or floodplain areas can cause greater requirements than the obstacle crossing itself. Approach conditions may be the prime factor in obstacle crossing and Keep the number of curves and grades at a minimum for efficient traffic flow over roads. All vehiceles have difficulty in negotiating sharp curves; even gentle curves decrease traffic capacity. Lay all routes with minimum curves by making the tangent lines as long as possible. Locating long tangents is influenced primarily by the terrain and limited by the following principles of efficient location: minimizing earthwork, avoiding excessive grades, and may dictate route location. Consider the approach with the obstacle when establishing the optimum route.

and available quantity of materials must meet the construction requirements. The proximity of a suitable base-course-material source is a critical planning factor.

## Ground Cover Marginal Material

All routes should avoid heavily wooded areas that require extensive clearing, lf this is not possible, the route should pass through areas having the least vegetation. Precede all earthwork by stripping unsuitable material.

## Required Areas

When planning the location of a project, consider using marginal materials nearby.

Using marginal materials for subbase and base construction and, as an aggregate in pavements is sometimes possible by using geotextiles, mechanical stabilization, or admixtures.

Often the use of marginal material is unavoidable. Where possible, poor -quality material should be excavated and replaced with more suitable material, or the project should be relocated.

## Flight-Way Obstructions

Airfields need large areas of relatively flat land to efficiently accomplish their mission. This usually restricts the number of sites that can be considered for airfield construction. Advance location and layout will avoid cramping necessary facilities. Frequently, the airfield must be spread over a large section to obtain the required area. This results in the construction of a complex network of taxiways and service roads.

When this is the case, keep in mind the ability to construct this connecting network to appropriate specifications.

Roads built on rolling or flat terrain seldom require large, lateral areas. Roads constructed in deep cuts or fills require proportionately greater lateral areas to account for slopes.

## Accessibility To Materials And

The safe operation of fixed- or rotary-wing aircraft requires the removal of all obstacles above lines specified by design criteria. These criteria depend upon the operating characteristics of the aircraft to be serviced.

For example, most heliports require an approach zone with a 10:1 glide angle (8:1 for short-duration operations), whereas heavycargo aircraft in the rear area require a glide angle as flat as 50:1. To achieve this glide angle, it is often necessary to remove vegetation and hills and perform extensive earthwork operations far from the airfield proper. Thus, avoid locations that require extensive work to achieve the necessary glide angle.

## Utilities

A similar clearance is required on the sides of runways. An area of specified width must be cleared of all obstacles and graded according to specifications.

## Sunlit Slopes

The efficient operation of airfields requires the use of electricity, water, gas, and sewer systems. Locating new airfields near existing utility systems can avoid the construction of new facilities or long transmission lines. A nearby railhead will help the construction effort.

lf tactical concealment is not required, locate roads on the sunny, exposed sides of valleys or hills, particularly in wet or cold areas. This permits the road surface and subgrade to dry rapidly, minimizes icy conditions, and makes maintenance easier.

Prevailing winds should also be considered Consider the quality and availability of construction materials when locating a facility. Obtain suitable base-course materials from existing pits and quarries whenever possible because much planning and effort are required to open a new quarry. The quality

## Site Selection And Reconnaissance

perse the facilities to minimize the effects of bombing or strafing attacks. It may be necessary to use ground troops in defensive positions against enemy ground action.

when locating roads. Prevailing winds will carry snow, rain, and sand onto the road -
way, if the orientation of the road is undesirable. Protective snow or sand fences should be oriented to take into account the prevailing winds.

## Future Expansion Tactical Considerations

Frequently, it is necessary to construct temporary roads or heliports or to improve landing strips to move personnel and materials.

When this is the case, consider the following tactical factors:
Due to the unpredictability of military operations, engineer troops are often required to modify and expand previously completed construction.

The road that is adequate for today's maneuvers may be inadequate for tomorrow's operations. Airfields built for small aircraft with a limited evacuation mission may have to be modified to meet more stringent design criteria for accommodation of high-performance aircraft, Improvement and expansion are a continuing job on all military construction.

Defilade. Locate all roads in a defilade position on the reverse side of a hill or ravine to avoid enemy observation and to provide cover from direct artillery or mortar fire.

Camouflage. When constructing a road or airfield in an exposed area, take advantage of all natural camouflage and concealment. Defense. Air fields in forward areas are prime targets for enemy air and ground attacks. When designing the airfield, dis-
Try not to construct a road or airfield in a restricted area where there is no possibility of expansion.

Design basic facilities so that they can be used as part of the expanded facilities. The ability to expand an existing route or facility will conserve personnel and material and permit rapid completion of future projects.

## Reconnaissance

Reconnaissance operations vary with the operational environment; the assigned mission: and the size, type, and composition of the reconnaissance element. An aerial, map, or ground reconnaissance is necessary to determine the best existing or best possible location for a future road or airfield.

The final construction plans and schedules are made with regard to the tactical and logistical situation and the construction time available. The reconnaissance report, submitted by personnel conducting the investigation, must be complete, comprehensive, and sufficiently detailed to permit careful analysis,

## Mission Reconnaissance-Party Capabilities

Thorough reconnaissance requires qualified, trained, and experienced personnel. The quality of the reconnaissance is directly related to the abilities of the party accomplishing it. This is especially true in airfield reconnaissance, which requires broader engineering judgment than any other engineer reconnaissance, Even a qualified civil The primary mission of a reconnaissance party is to find a site meeting most requirements, to recommend a general layout and construction plan, to estimate the work required to construct the facility, and to obtain the data needed to determine a completion date and detailed construction sched -
ules. When the reconnaissance mission is complete, the reconnaissance report serves as the basis for tactical plans and construction schedules.

## Briefing

engineer with civilian or military experience requires special training for this activity. It is unusual for one person to be proficient in all the items a thorough reconnaissance must include.

Therefore, the assignment of personnel to the party must provide for its overall efficiency as a unit. The party must be selected with regard to the conditions it may confront.

The briefing tells the reconnaissance party exactly which site or area is to be reconnoitered, what is already known about the area or site, and what information the party is expected to obtain, Details concerning the time or methods of reporting the information will be included in the briefing. The party must also know the type of facility for which it is reconnoitering. If a site has been tentatively selected or if some information has already been determined from a preliminary study, the party must be informed. Otherwise, time and effort will be wasted. A soils or terrain analyst should brief the reconnaissance party, if such an expert is not able to accompany the party, If available, aerial photos should be used in the briefing.

The following information is necessary for a full understanding of a particular reconnaissance mission and should be covered in the briefing:
Factors to be considered include the road - net, the general nature of the terrain, the weather, the prevalence of land mines, the attitude of the civilian population, and the amount of enemy resistance the party may expect.

These factors also influence the equipment assigned to the party. The equipment should include all items necessary for soil and topographic surveys, mobility, security, and good communication. The success of the mission depends on proper personnel and equipment. One without the other will not accomplish the needed results, If available, a soils or terrain analyst is a valuable member of the reconnaissance party, If an analyst is not available, obtain soil samples for later analysis.

## Steps In Reconnaissance

Reconnaissance involves the steps that follow.

Z

## Planning

Planning is concerned with the formation of a reconnaissance mission. It involves the coordination of reconnaissance efforts by appropriate headquarters, the estimation of needs, and the assignment of a reconnaissance mission. Both ground and aerial methods should be integrated. This is a responsibility of the engineer brigade, the group, or the battalion, not the individual reconnaissance party. Reconnaissance missions are based on user requirements as governed by ground forces. Maintain close liaison with all headquarters to achieve proper coordination, Improper coordination results in duplication of effort in some areas and inadequate reconnaissance in other areas.

Z
The general area to be covered, if an area reconnaissance is to be conducted; or the exact location of the site or facility to be investigated, if a specific reconnaissance is to be done.

The nature of the proposed facility; the
types of vehicles or aircraft scheduled to use it; the length of time such use is anticipated; and the minimum requirements concerning dimensions, grades,
and clearances. (These items are covered by reference to the applicable standard layout and specifications published by the joint force commander in
the theater. They are usually familiar
to the reconnaissance officer but should
be kept for reference.)
Z
The anticipated vehicle traffic and number of aircraft and personnel to be initially accommodated at the proposed facility. (When dealing with airfields, figures are often given in terms of the number and type of aviation units to be
assigned to the installation. Strength and equipment figures should also be
available for reference.)
- Alternative and emergency-landing instructions.
- The minimum amount of aircraft service, repair facilities, and special requirements needed.
- Location of available aviation petroleum
supplies.
- The expected future expansion of the
new facility.
- Location of the forward flying line.
Z The expected construction time available for building support facilities.

## Preliminary Study

Z Information previously obtained about
the proposed project.
- The essential details concerning the
report and how, when, and to whom the
report should be made,
The preliminary study consists of studying the information obtained during the briefing, conducting a map reconnaissance of the area involved, studying aerial photos, delineating soil boundaries, assembling other available preliminary information, and planning and preparing for the actual reconnaissance.

When the reconnaissance party is to be away from its parent unit for a lengthy, continued reconnaissance, the following additional instructions must be covered in the briefing:
Sources of information that may be useful in the preliminary planning of reconnaissance missions and in the preliminary study of a specific mission are discussed below. Such information must be verified by ground reconnaissance.

- The location where rations, clothing,
and equipment replacements can be
drawn.
Z The source from which petroleum, oils,
and lubricants (POL) supplies can be drawn.
Z The service facility where vehicle maintenance can be obtained.
- The form of communications to be arranged; for example, radio, messenger,
or telephone.
- Intelligence dossiers that provide planning data and other information on a
particular airfield site or route that may
already exist. These dossiers are the result of previous reconnaissance or reconnaissance plans and can usually
be obtained if adequate coordination is
maintained with higher headquarters
and other units engaged in reconnaissance. Similarly, reports of aerial reconnaissance that were conducted in anticipation of later ground reconnaissance may be available from adjacent or
higher units.
When ground reconnaissance is ordered ahead of forward ground-force elements, the following additional instructions are necessary:

Z Friendly-force situation. - Known enemy-force situation,
- Location of adjacent friendly units.
The following instructions are applicable only to parties engaged in air reconnaissance:

- Strategic and technical reports, studies,
and summaries on specific areas of actual or potential military importance are
prepared by the Office of the Chief of Engineers and subordinate agencies. These reports provide the best data available at the time they were printed. Topographic, geologic, and soil maps, as well as data on the climate and groundwater tables, are usually included. These reports may contain information on water supply, construction

## Air Reconnaissance

materials, vegetation, and special physical phenomena.

Air reconnaissance involves a general study of the topography, drainage, and vegetation of the area. The construction problems, camouflage possibilities, and access routes should be visualized. Usually the specific ground-reconnaissance procedure is planned by selecting, from the air, areas that need investigating and by determining what questions need answering. Air reconnaissance can provide valuable negative information by eliminating unsuitable sites, but it cannot be solely relied on for positive information.

Z Army and Air Force periodic intelligence
reports are important, reliable sources
of information. Intelligence reports are
usually prepared in the interior zone,
but periodic intelligence reports are
field-prepared reports of all-around force elements. They include facts
learned by prisoner-of-war interrogations, tactical data, reports, records, and interrogation of local inhabitants. Intelligence reports are used to prepare
strategic and technical reports.

## Ground Reconnaissance

- Road, topographic, soil, vegetation, and
geologic maps published by friendly or enemy govern ments and agencies are
sources of information. Maps showing
the suitability of terrain for various military purposes may be of considerable value in planning roads and airfields.
While air reconnaissance can effectively reduce the amount of ground reconnaissance, it cannot replace ground reconnaissance. It is on the ground that most questions are answered or that questions tentatively answered from the air are verified.

Often ground and air reconnaissance are not separate missions, A continuing air reconnaissance may be interspersed with specific ground reconnaissance.

Z
Aerial photographs show the approximate amount of grading and excavation required, the total area and extent of promising sites, the extent of
necessary clearing, the presence of flying hazards (for airfields), and the
area and local drainage conditions.
The reconnaissance party must always submit its report on time. Reports are submitted for all sites investigated, even if the reconnaissance party considers the site unsuitable.

Z If time and facilities are available,
topographic maps should be prepared from aerial photographs.
Z Weather reports published by
governmental agencies and the Air
Force Air Weather Service are used to
determine critical factors for runoff determination, prevailing winds, and cloud cover which will affect construction and future operations.
Z Aeronautical reports and charts provide
an overview to help plan aerial reconnaissance.
Z Indigenous governmental agencies may
provide valuable information on a great
diversity of subjects.
Full details on the method, place, and time of submitting reconnaissance reports should be included in the instructions given to the reconnaissance party. Reconnaissance reports can be submitted in writing or by radio. A radio report should be followed by a detailed written report. Standard reconnaissance reports are preferred. They ensure full coverage of needed information and allow a comparative evaluation of two or more sites. Standard formats are helpful in comparing sites which have been reconnoitered by different parties. They simplify each party's work in preparing reports.

## Reporting

- Identification of available sources of
water.
- Supply evaluation of construction
materials in the area of operations.
- Discussion of cover and concealment.

## Ground Reconnaissance

Military roads and road networks are defined according to location and use.

They are classified according to width, surface, and obstructions. Terms and formulas approved by the member nations of the NATO, the Southeast Asia Treaty Organization (SEATO), the United States, the United Kingdom, the Canadian and Australian Armies Nonmaterial Standardization Program, and other treaty nations are covered in FM 5-36.

Abbreviations, symbols, and notations used in route reconnaissance (described in FM 5- 36) may also be used in airfield reconnaissance. Information given in road reconnaissance reports is useful in reporting on access roads to airfield and heliport sites.

## Air Reconnaissance

The composition of the ground-reconnaissance party depends on the scope and extent of the mission and the nature of the terrain it must traverse. The composition depends upon the probability of contact with the enemy, the attitude of the civilian population, and the prevalence of mines in the area to be reconnoitered. Table 2-1, page 2-10, provides a list of personnel suitable for an airfield reconnaissance. The list can be modified to meet the particular needs of the situation.

All personnel involved should be trained in ground reconnaissance. It is important that the person in charge and the assistant be well versed in all aspects of reconnaissance.

An air-reconnaissance team generally consists of only two members: the pilot and the engineer observer. Having the officer in charge of the ground-reconnaissance party act as the engineer observer is advantageous and should be arranged when possible.

Time is saved and errors of omission are minimized when a report from the engineer observer to the officer in charge of the ground-reconnaissance party is not necessary except as a matter of record, The pilot can also assess the site and make the appropriate recommendations.

All equipment needed to carry out the assigned tasks should be taken. The equipment varies as the composition of the party varies.

A typical list of equipment suitable for the party is listed in Table 2-2, page
2-10.

Two -place, fixed -wing aircraft or two-place helicopters are suitable for most air-reconnaissance missions, Reconnaissance of enemy-occupied airfields is best accomplished with modified tactical aircraft.

Map and air studies are not substitutes for ground reconnaissance; they only reduce the amount of ground effort required.

Ground reconnaissance should determine the following information:

- Estimated grades to be encountered.
Effective air reconnaissance should provide the following information:

- Determination of terrain features.
Z Description of obstacles.
- Evaluation of LOC.
- Estimated amount of clearing involved.
This includes trees, tree stumps, and
boulders. Sometimes objects such as buildings and concrete foundations are included.
Z Assessment of suitability of the area for
various types of construction.
Z Consideration of debris generated
during clearing operations. In some
- Estimated amount of earthwork necessary, the approximate balance between
cut and fill, and the necessity for long
hauls of earth material.
cases, the trees removed may be used in the construction operation. Details of clearing operations are discussed in Chapter 4 of this manual.

- Errors or discrepancies on the maps
from which the site was tentatively selected and the effects of such errors on the selection.
- Nature of soil encountered, field determination of gradation, percentage of fine-gradient materials, and plasticity characteristics.
Z Local rainfall data and other pertinent
information about seasons and weather
obtained through local inhabitants or other sources,
- Conditions of streams at crossing sites;
width, depth, and velocity of the stream;
condition of the banks and streambed; and indications of high water levels.
- Information or observations which affect
the final facility location.
- Relationship with the local population.
- Presence or absence of local construction materials, including possible sources of sand, gravel, cement, tar, asphalt culvert pipe, and lumber, Local con -
struction capabilities and labor conditions are included.

## Route And Road Reconnaissance

Thorough reconnaissance is essential in the selection of roads. It starts with a study of available maps and aerial photographs.

Aerial reconnaissance provides valuable information. Detailed information, however, can be obtained only by ground reconnaissance. Reconnaissance performed in connection with military LOC is route reconnaissance. Reconnaissance to check existing roads is road reconnaissance. Reconnaissance to determine the location for a new road is location reconnaissance.

A deliberate route reconnaissance is detailed.

It provides the data necessary for a thorough analysis and classification of significant features along a route, including repair or demolition procedures, if required, An overlay is used to point out exact map locations, and enclosures are attached to the overlay.

The enclosures are DA Reconnaissance Report forms that provide a permanent record and ensure enough detail is recorded, The use of these forms is explained in FM 5-36.

## Route Reconnaissance Road Reconnaissance

Road reconnaissance is conducted to determine the traffic capabilities of existing roads and to provide more detailed information than is needed for route classification. It may include enough information to develop work estimates for improving the road to certain standards of trafficability DA Form 1248, shown in Figure 2-2, pages
2-12 and 2-13, is used to record this information. Maps, overlays, and sketches are used as necessary.

Route reconnaissance includes gathering information about roads, bridges, tunnels, fords, waterways, and natural terrain features that may affect the movement of troops, equipment, and supplies in military operations. Route reconnaissance may be hasty or deliberate.

A hasty route recon -
naissance is conducted to determine the immediate trafficability of a specified route and is limited to critical terrain data. It may be adequately recorded on a map overlay or sketch and be supplemented by reports about various aspects of the terrain,

## 2-12 Site Selection And Reconnaissance

weather to determine the effects of these conditions. Maintenance requirements based on periodic reconnaissance must be coordinated with the agencies using the roads to ensure proper standards of maintenance and to avoid work on roads no longer needed.

## Location Reconnaissance

The most important factor in planning military roads is making maximum use of the existing roadnet.

Subject to the requirements of the tactical plan, the existing roadnet must be adapted to military use before undertaking new construction. Existing roads should be surveyed at the earliest opportunity to determine their condition and capacity. Time is saved by improving an existing road rather than constructing a new one.

When a new road is necessary, the first step is the location reconnaissance. This requires reconnaissance of all possible routes to ensure selection of the best route. The main objective of a location reconnaissance is to locate a new road that will withstand anticipated traffic and provide the best possible operating conditions.

is Periodic road reconnaissance is conducted to obtain information about the road situation in a specific area. A situation map is prepared and kept current to show the condition of roads, the density of traffic, the need for maintenance work, and the results of maintenance. Periodic reconnaissance important during wet or unusually dry

## Engineer Reconnaissance

materials, resources, terrain features, and facilities that have engineer implications.

Special engineer reconnaissance obtains detailed information regarding an investigation of a specific site or evaluates the potential use of an undeveloped facility such as an airport or heliport. DA Form 1711-R is a required enclosure to the route reconnaissance, as specified in FM 5-36.

Engineer reconnaissance is often conducted in conjunction with deliberate route reconnaissance to determine route conditions (including work estimates) and to locate construction materials to improve or maintain the route.

It is either a general or special reconnaissance.

General engineering reconnaissance gathers engineering information of a broad nature within the operational area to locate and evaluate construction

## Airfield Reconnaissance

photograph reconnaissance, supplementing data from reports of aerial observers or intelligence sources.

These sites may be undeveloped potential sites or operating enemy installations.

Reconnaissance should begin as soon as possible.

Airfield reconnaissance differs from roadlocation reconnaissance, described in FM
5-36, in the scope of information. An airfield project involves more personnel, machine-hours, and material than a road project. Air traffic imposes more severe limitations on its traffic facilities than vehicular traffic. Consequently, the site seIected must be the best site available.

## Planning Airfield Reconnaissance

For an undeveloped potential site, the object of the reconnaissance is to verify or amend tentative selections and layouts and to estimate the material, equipment, and troop requirements for the construction planned. If it is a captured enemy airfield, Tentative airfield sites are selected within enemy territory using map and aerial effort necalso be rea decision is needed on whether to use the captured field or develop a completely new site. Estimates of the engineering essary to restore the airfield may quired.

angle. This runway location is unsuitable according to the specifications. The template is useful to the reconnaissance officer and to the preliminary planning group. Prepared templates can measure distances in feet, yards, miles, and kilometers by placing gradations along their edges.

which our be devel-
New airfields added to an area in aircraft are already operating can oped in the following manner:

## Procedures For Airfield Air Reconnaissance

The general procedure for an air reconnaissance follows:

- Select the best available map of the area
in which the new airfields are to be located. Draw a 5-mile-diameter circle around existing airfields and shade them. Note all high-tension, electric transmission lines and shade a 2-milewide strip centered on these lines. Locate and shade all similar obstructions on the map. Assault or hasty airfield selection is discussed in Chapter 10 of FM 5-430-00-2/Air Force Pamphlet (AFPAM) 32-8013, Vol 2.
En route to a particular site or a general area, the engineer notes open borrow pits, large stockpiles of construction material, rail and road accesses to the site, and errors on maps that have been studied. The pilot plays an important role on the reconnaissance team.

Besides chauffeuring the engineer officer, the pilot considers approaches, mental hazards, and physical obstructions related to tactical aircraft that may use the proposed installation. A pilot who is familiar with operational requirements and the performance characteristics of tactical aircraft is more valuable than one who is not.

- Confine the study for potential airfields
to the unshaded parts of the map. Look
for sites of sufficient area, preferably flat with good natural drainage, unobstructed air approaches, and accessibility to routes of communication. Assign
the most likely sites to reconnaissance
parties for appropriate air and ground investigation.

## Selecting Runway Location

The engineer observer assesses possible construction problems at a potential site. The engineer selects tentative sites and directs questions to the ground reconnaissance party. The engineer receives the pilot's suggestions concerning the flying-related characteristics of the sites investigated and modifies estimates according to these recommendations.

To be effective as an engineer observer the officer should possess the following qualifications:

- Knowledge of road and airfield requirements and construction procedures and experience in airfield work.
A convenient way of selecting a runway location at a site that meets glide-angle requirements is to prepare and use the ah-field-siting template illustrated in Figure 2-3, page 2-16. This template can be drawn on acetate or heavy cellophane for use on any map to meet specifications for flight way, horizontal approach, and glide angle. When placed on the map, the template shows land forms and natural or manufactured obstacles that are in or above the plane of the glide angle. In Figure 2-3, any hill within the approach zone at a distance of 8,000 feet from the end of the overrun and having an elevation of more than 160 feet above that of the end of the proposed runway, is in a 50:1 glide

- Immunity to airsickness. An airsick officer cannot effectively accomplish air reconnaissance. Any tendency of the engineer observer to become airsick is
greatly enhanced by the continual concentration on a particular site and by
the steep turns and maneuvers essential to continued observation.

made on the map, but additional trips should be flown across the area, if necessary.

After the runway has been selected, an initial low pass is made at about 50 yards to one side of the proposed centerline. A
second pass in the opposite direction is flown on the other side of the centerline.

Both of these flights should be made at a constant air speed so the runway length can be estimated by multiplying the air speed by the average flight time.

- Proficiency in map reading. Upon approaching a designated or tentatively selected site for reconnaissance, the normal altitude for the first circuit is approximately 300 feet. Nothing more than orientation can be accomplished in
this circuit. Sometimes a site tentatively selected during an area search can be eliminated during this circuit or the
next few passes.

NOTE: The length usually is overes-
timated when flying at low air speeds if a
strong wind is blowing along the center-
line. This can be decreased if the distan-
ces obtained by two passes in opposite

Similar second and third passes are flown.
During these circuits, obstructions, main
slopes, and general features are noted. The
pilot begins to formulate an estimate of the
flying-related characteristics of the field.
Pinpoints for the ends of the runway are

directions along the centerline are averaged (assuming the wind is constant).

A final circuit is then flown at approximately 200 feet. During this trip, the ends and centerline of the runway are given a final check, and the pilot completes the appraisal of the field's flying suitability.

In departing, the observer reviews dispersal areas and again checks access roads. Additional passes over the site are made if questions arise as a result of this last check.

An air reconnaissance report similar to Figure 2-4, page 2-18, may be used.

When the site to be surveyed is reached, the most likely locations for a runway must be investigated. If the terrain is open enough to permit good observation, these locations may be quickly determined. Locations for runways are traversed by vehicle or on foot. A rough survey of each selected runway is carried out immediately. Lengths are paced, critical slopes are measured with a clinometer, and directions are determined with a magnetic compass. The type of soil is noted and observations of a few samples are made. A preliminary check of a possible runway can be made in 15 minutes, if the country is reasonably clear and open.

An area reconnaissance then proceeds by similar inspection of other possible sites, Complete notes must be kept to avoid reviewing sites already checked however, a reinvestigation of the final site selected and any selected alternative sites may sometimes be necessary.

## Procedures For Airfield Ground Reconnaissance

If the country is rough and is not sufficiently open to permit a quick selection of runway locations, a detailed search must be made on foot. The reconnaissance officer, accompanied by necessary personnel, follows the centerline of the area for the runway and dispersal areas. The reconnaissance officer notes on a large-scale map or sketch all obstacles that cannot readily be eliminated, such as gullies, rock outcrops, and swampy areas.

Examination of the results discloses the possible runway locations.

The general procedure for ground reconnaissance follows:
The ground-reconnaissance phase is preceded by map and air reconnaissance to discover what specific sites and questions warrant ground investigation.

The best runway location is selected by considering these centerline investigations with prevailing wind direction, air approaches, glide angles, groundwater conditions, discharge areas for collected runoff, clearing, grubbing, and earthwork. If a suitable runway does not exist, a negative report on the site is submitted. Once the selection of a potential runway is made, a careful and detailed walk of the centerline of each runway is made to recheck its suitability. Stakes are driven at each end of the runway and prominent features are properly referenced to later expedite the location of the selected runway by construction unit surveyors. The survey sergeant of the reconnaissance party stakes out the centerline of the runway and runs a ground profile of it at the centerline and at each shoulder line. Levels are taken at 500-foot intervals and En route to the site or sites to be investigated on the ground, the reconnaissance party should properly record the general condition of roads and bridges, the location of usable or repairable railheads, the locally available materials and equipment, and the potential water points. When reconnaissance of a definite site is involved, a more detailed observation of the access route should be made. A check must be made of bridge capacities, overhead clearances, and features that might hinder the movement of construction equipment to the site, as well as the suitability of railheads and sidings for use in construction. A detailed report of the quantity and quality of materials available at quarries, pits, and stockpiles must be prepared.

mat is shown in Figure 2-5:
at intermediate breaks or slope changes. In eluded in the report. A suggested report forflat country, this interval may be increased to as much as 1,000 feet. If an alternative runway is selected, a similar survey is conducted for that runway, if time permits.

The soils analyst conducts a field investigation of the soil conditions at the site, Refer to Chapter 7 of this manual for more information about soil conditions.

When possible, local inhabitants are interviewed to check information already obtained and to obtain more information.

Several opinions should be obtained. Questions should be phrased to provide the best comparison of answers. Information must be weighed carefully with regard for the credibility of each person questioned. The reconnaissance of a designated site should be accomplished in one day, unless Previously acquired information is checked at the site for accuracy. Errors, including discrepancies on maps and mistakes in aeriaI photograph interpretations, are informat in Figure 2-7, page 2-22. The tactical situation may dictate the amount of information transmitted. Unit standing operating procedures (SOPS) should indicate what information is critical for radio reports. A complete, written report should follow the radio report.

hostile forces delay the work. A specific reconnaissance of a captured enemy airfield is somewhat different from that outlined above. Detailed information about the existing facilities and their condition is desired.

The specific information needed is indicated on the suggested form for reconnaissance reports of captured enemy airfields shown in Figure 2-6.

The formats illustrated in Figure 2-4, page
2-18; Figure 2-5, page 2-19; and Figure 2- 6, are suggested for written reports. The reports should include the same items of information shown on these forms. Suitable sketches should be attached to all written reconnaissance reports. Figure 2-8, page 2-
23, is a typical sketch.

When the reconnaissance parties are operating at a considerable distance from the headquarters directing the reconnaissance, it is imperative that an initial report reach headquarters without delay. Use organic radio equipment and the suggested message Surveys and Earthwork Operations Construction Surveys Construction Stakes

## Earthwork Surveys And Operations

Construction surveys are initiated when new construction is
necessary. These surveys reveal the kinds of stakes to be used:
provide data for earthwork estimation, including which method
of estimation to use; and provide information for use on the
mass diagram.
               The finished survey books should be filed with
the construction project records of the Operations and Training
Officer (US Army) (S3).

Earthwork operations are one of the most important construction
aspects in road and airfield construction. Earthwork reqires
the greatest amount of engineering effort from the standpoint of
personnel and equipment.
                           Therefore, the planning, scheduling,
and supervision of earthwork operations are important in ob-
taining an efficiently operated construction project.

## Construction Surveys

ducted for a deliberate project in the communications zone.

The quality and efficiency of construction is directly proportional to the number and extent of surveys and other preplanning activities. The principles and techniques of field surveying are discussed in detail in technical manual (TM) 5-232
and FM 5-233.

Construction surveying is the orderly process of obtaining data for various phases of construction activity. It includes the following surveys: reconnaissance, preliminary, final location, and construction layout. The reconnaissance and preliminary surveys are used to determine the best location. The remaining surveys are conducted after a location has been established.

After completing a thorough construction survey, transfer the design information from paper to the field by construction stakes.

These stakes are the guides and reference markers for earthwork operations.

The purpose of construction surveys is to control construction activities. The number and extent of surveys conducted is governed by the time available, the standard of construction desired, and the il bilit f l d t i l I
i

## Reconnaissance Survey

2 inches by 2 inches and the guards are flat stakes, about 3/4 inch by 3 inches.

## Horizontal Control

The reconnaissance survey provides the basis for selecting acceptable sites and routes and furnishes information for use on subsequent surveys.

If the location cannot be selected on the basis of this work, it must be determined by the preliminary survey.

## Preliminary Survey

The purpose of horizontal control is to accurately determine points for the various facilities of an engineering project. Establish permanent, well-marked points for horizontal control and reference them at the site before construction begins. On a large facility, establish a grid network and use it for this control. Tie the network into the military grid system in the particular area, if such a system has been established. On an airfield, place control points beyond the clear zone.

These points define the centerline of the runway and other important sections of the airfield.

The preliminary survey is a detailed study of a location tentatively selected on the basis of reconnaissance, survey information, and recommendations. It consists of running a traverse along a proposed route, recording topography, and plotting results.

For roads, it may be necessary to conduct several preliminary surveys if the reconnaissance party has investigated more than one suitable route. Establish, station, and profile the route centerline with horizontal and vertical control points set. Take crosssection readings to allow rough calculations of the earthwork involved. (Sometimes cross sections may be taken during the reconnaissance survey if the conditions warrant.) If the best available route has not been chosen, select it at this time.

As the taxiways and other facilities are laid out, establish and reference new control points. In laying out the centerline, place target boards at each end of the runway so the instrument person can make frequent checks on alignment while the line is being staked out.

Target boards may be set up on any line that requires precision alignment. Reference control stakes to ensure replacement, if they are disturbed or lost.

Locate the target board just beyond the outermost control-point stake.

## Vertical Control

The airfield survey consists of establishing controls, noting terrain features, measuring glide-angle clearance, making soil profiles, and investigating drainage patterns and approaches. Accurately establish the final centerline during the survey.

## Final Location Survey

Vertical control methods determine the difference in elevation between points. If available, establish a level reference surface or datum from a known bench mark. Differences in elevation, with corrections, are subtracted from or added to this assigned value, resulting in the elevation of the points. Take the datum of the bench mark system from a known elevation or barometer reading or make an arbitrary assumption.

## Construction Layout Survey

When time permits, conduct a final location survey.

Establish permanent bench marks for vertical control and well-marked points for horizon tal control. These points arc called hubs because of the short, square stake used.

On most surveys, the hub is driven flush with the ground, and a tack in its top marks the exact point for angular and linear measurements. The hub location is indicated by a flat guard stake extended above the ground and driven at a slope so its top is over the hub. Hubs are The construction layout survey is the final preconstruction operation. It provides alignments, grades, and locations that guide con -
struction operations. The survey includes determining exact placement of the centerline; laying out curves; setting all culvert sites; and performing remaining stakes, grades, and shoulders;
quired to begin construction.

other work re-
Continue this staking out necessary structures; laying out survey until construction is completed.

## Construction Stakes

- The horizontal distance from the centerline to the stake location.
Z The side-slope ratio used on slope
stakes.
Use construction stakes for centerline, slope, offset, shoulder, grade, reference, ditch, culvert, and intermediate slakes and for temporary bench marks. The stakes should be approximately 1 inch by 3 inches by 2 feet. Use finished lumber when possible. If it is not possible to usc finished lumber, usc small trees or branches blazed on both sides and cut to length. Finished grade stakes and temporary bench marks are 2 inches by 2 inches by 12 inches.

Place stakes using a three- to five-person crew equipped wtth transit, level, rod, tape, ax, sledgehammer, and machete.

The number and location of stakes used differ between roads and airfields. A typical set of construction stakes consists of a centerline stake and two slope stakes and is referred to as a three-point system. Point one is the centerline of the facility.

Points two and three are the construction limits of the cut and fill at right angles to the centerline.

## Centerline Or Alignment Stakes

The primary functions of construction stakes are to indicate facility alignment control elevations, guide equipment operators, and eliminate unnecessary work. They also determine the width of clearing required by indicating the limits of the cut and fill at right angles to the centerline of a road.

The centerline or alignment (hub) stakes, shown in Figure 3-1, are placed on the centerline of a road or air field and indicate its alignment, location, and direction. They are the first stakes placed and must be located accurately.

These stakes are used as reference points in locating the remaining stakes.

Centerline stakes are placed at 100-
foot (or 30-meter) intervals.

On rough ground or sharp horizontal and vertical Mark and place construction stakes to conform to the planned line and grade of the proposed facility.

Use colored marking crayons to mark the stakes. Use a uniform system so the information on the stakes can be properly interpreted by the construction crew.

Construction stakes indicate-

Z The stationing or location of any part of
the facility in relation to its starting
point. If the stake is located at a critical point such as a point of curvature (PC), point of intersection (PI), or point
of tangency (PT) of a curve, note this on the stake.
Z The height of cut or fill from the existing
ground surface to the top of the subgrade for centerline stakes or to the
shoulder grade for shoulder or slope
stakes.
curves, place the stakes closer together.

On horizontal curves, also stake the PC, PI, and PT. On vertical curves, also stake the point of vertical curvature (PVC), the point of vertical intersection (PVI), the point of vertical tangency (PVT), and the low point (LP)
or high point (HP) of the curve.

Place centerline stakes with the broad sides perpendicular to the centerline. The side of the stake that faces the starting point is the front. Mark the front of the stake with a   for centerline and, if applicable, PC, PI, or PT. Also mark on the front the distance from zero or the starting point in 1 00-foot stations and the fractional part of a station, if used, For example,        marked on a stake indicates it is 654.22 feet from the origin of the facility and is known as the station of this point. Stations are used in locating sections of construction and in preparing reports. PIace the amount of cut or fill required at the station on the reverse side of the stake.

A cut is marked C; a fill, F. A centerline stake, placed at station 78 + 00 and requiring a fill of 6.0 feet to bring this station up to the final grade line, would be placed and shown as indicated in Figure 3-1, page 3-3.

The amount of cut or fill indicates the difference between the final grade line and the ground line where the stake is emplaced. A
point on the stake is seldom used as the line of reference to the final grade.

determining the width of clearing necessary. The area to be cleared usually extends 6
feet beyond the slope stakes. Set slope stakes on lines perpendicular to the centerline (one on each side), at points where the cut and fill slopes intersect the natural ground surface.

Stakes at points of zero cut or fill are placed sloping outward from the centerline.

To prevent misinterpretation of the amount of cut or fill, mark decimal parts of a foot, as shown in Figure 3-1. The decimal part is written smaller, raised, and underlined. Facing the direction of increasing stations, the centerline forms the dividing line between the right and left sides of the area to be graded. When facing either side of the centerline, it is customary to refer to the areas as the right or left side.

Sloping the stakes outward allows the equipment to work to the stake without removing it. The slope indicates the direction of the centerline of the road and enables the equipment operators to read the stakes more easily. Place slope stakes at 100-foot intervals on tangents and at 50-foot intervals on horizontal or vertical curves, Whenever a sharp break in the original ground profile occurs, it should be staked.

## Slope Stakes

Slope stakes, shown in Figure 3-2, define the limits of grading work. When used in read work, they can be used as guides in The front of a slope stake is the side facing the centerline. On this side of the stake, mark the difference in elevation between the natural ground elevation at this point and the finished grade at the edge of the shoulders.

Under this figure, place another figure that indicates the horizontal distance from the centerline of the road to the slope stake. Place the station number on the other side of this stake. Below the station number, indicate the appropriate slope ratio.

Figure 3-2 shows the proper markings for a slope stake in a typical situation.

## Offset Stakes

Equipment used on a cut or fill section may destroy or remove many of the grade (centerline, shoulder, or slope) stakes. To prevent loss of man-hours and repetition of survey work, caution construction crews to protect grade stakes whenever possible. Place offset stakes beyond construction limits to avoid resurveying portions of the road to relocate these stakes.

Figure 3-3 shows offset stakes used to relocate the original stakes.

## Finish-Grade Stakes

Place offset stakes on a line at right angles to the centerline of the facility. From these, the slope stakes can easily be located. After relocating a slope stake, relocate the centerline stake by measuring toward the centerline of the road the horizontal distance indicated on the slope stake and placing the new centerline stake there.

Use wooden stakes, 2 inches by 2 inches, with tops colored red or blue, for finishgrade stakes.

Blue or red tops, as they are called, indicate the actual finished elevation of the final grade to which the completed facility is to be constructed. They are used when the grade is within a short distance of the final elevation. Do not use these stakes in combat road construction except in areas with steep slopes. This type of stake normally requires a guard stake to protect it and indicate its location. On large projects, it may be impractical to use guards with each stake.

An offset stake contains all the information given on the original slope stake plus the difference in elevation and horizontal distance from the original slope stake to the offset stake. Mark the offset distance on the front of the stake and circle it to indicate it is an offset reference. If the offset stake is at a different elevation from the slope stake, the cut or fill value must be increased or decreased by the difference in elevation. An offset stake placed a horizontal distance of 10 feet from and 1 foot above the right slope stake would be placed and marked as shown in Figure 3-3. Coordination between the surveyor and grade supervisor concerning the meaning of the markings is most important regardless of the type of marking used.

There are no markings on finish-grade stakes other than the color on the top. These stakes may be set for use with the top of the stake exactly at the finished grade or with the top of the stake above the finished grade, as decided upon by the surveyor and construction foreman.

sect at approximately right angles. Place them outside the construction limits, and indicate their location by blazing trees or additional stakes.

Normally, the location of the reference stakes can be obtained from the surveyor's notebook.

## Culvert Stakes

With the stakes set and marked at a predetermined distance above the finished grade, stretch a string between two stakes across the work and use a graduated ruler or stick to check the elevation. On an airfield layout, place these stakes along the centerline, edge of pavement, intermediate lines, shoulder lines, and ditch slopes. For road work, place stakes along the centerline and the edge of the shoulder; they may or may not be placed on the slopes.

## Reference Stakes

Culvert stakes are located on a line parallel to and offset a few feet from the centerline.

The information required on the culvert stakes includes the distance from the stake to the centerline, the vertical distance to the invert, and the station number. Once the survey crew has finished staking out the culvert, the construction supervisor can place the pipe accurately by using batter boards.

## Bench Marks

Many hubs marking the location of highways and airfields are uprooted or covered during construction. They must be replaced, often more than once, before construction is completed. AS an aid in relocating a point which may become hidden by vegetation, or as a means of replacing points which may have been destroyed, measurements are made to nearby permanent or semipermanent objects. This process is known as referenceing or witnessing a point. On many surveys, permanent objects may not be available as witnesses.

In such cases, additional stakes may be driven.

These stakes usually are approximately 2 inches by 2 inches by 18 inches.

Vertical control of a road or airfield must be maintained during construction. To do this, points of known elevation must be established. Obtain elevations from permanent monuments, known as bench marks, established by geodetic surveys. From these bench marks, run a line of levels and set temporary bench marks (TBMs). On small projects the TBMs frequently are set by running the levels from a point of assumed elevation.

This is especially true of construction in combat areas. Usually, TBMs are placed at 500- to 1,000-
foot (or 150- to 300-meter) intervals and are placed off the limits of construction. Stakes 2 inches by 2 inches, solidly emplaced in the ground, may be used for this purpose.

However, a nail driven into a tree, a manhole cover, or a pipe driven into the ground may also be used.

Frequently, reference points serve as TBMs. The TBMs are set before setting the centerline stakes because vertical control must be established before construction begins.

There are no markings on a reference stake.

A point can be referenced by a known distance and a known angle or by two known distances. A transit must be used in the first case and may be used to advantage in the second, The method of using two known distances can be used, however, when a transit is not available. Place two points at measured distances from the point to be referenced.

Use two tapes to relocate the original point or stake. Hold the zero end of one tape on one reference point and the zero end of the other tape on the other reference point. The point of intersection of the two tapes at the respective distances gives the location of the point in question.

## Earthwork Estimation

Earthwork computations involve the calculation of earthwork volumes, the determination of final grades, the balancing of cuts To be of most value in replacing a missing station or point, the reference stakes or witnesses will be less than 100 feet from the point and, if possible, the arcs should interand fills, and the planning of the most economical haul of material. The exactness with which earthwork computations are made depends upon the extent and accuracy of field measurements, which in turn arc controlled by the time available and the type of construction involved. To plan a schedule, the quantity of earthwork and the soil and haul conditions must be known so the most eficient type and quantity of earthmoving equipment can be chosen and the appropriate time allotted. When time is critical, the earthwork quantities are estimated either very roughly or not at all. When time is not critical, higher construction standards are possible and earthwork quantities are estimated and con trolled by more precise methods.

## Fundamental Volume Determination

Plot ground elevations from the surveyor's notes.

Make a sectional template of the subgrade that shows the finished subgrade and slopes plotted to the same scale as the cross sections.

Superimpose the template on the cross section and adjust it to the correct centerline elevation. Trace the template and extend the side slopes to intersect the original ground.

If the section involves both cut and fill, draw only the appropriate lines of each template. When the sections are completed, begin the end-area measurements, then determine the volume. Of the several satisfactory methods of measuring the end areas, only the trapezoidal, stripper, double-meridian (triangular), and planimeter methods will be described in this manual. The method chosen will depend upon the time available, the accuracy desired, the aids at hand, and the engineer's preference.

The volume of a rectangular object may be determined by multiplying the area of one end by the length of the object, This relationship can be applied to the determination of earthwork by considering road cross sections at the stations along the road as the end areas and the horizontal distance between cross sections as the lengths.

The end areas of the cross sections must be computed before volumes can be calculated.

## Trapezoidal Method Methods Of End-Area Determination

The trapezoidal method is widely used to determine end areas. The computations are tedious, but the results are accurate. In using the trapezoidal method, the area of any cross section is obtained by dividing the cross section into triangles and trapezoids, computing the area of each part separately, and taking the total area of the verticals to the ground line (Figure 3-5, page 3-8) in order to divide the cross section into two triangles and two trapezoids. Make the assumption that the ground is perfectly straight between these selected points on the ground line. While this is not usually correct, the assumption is within the accuracy normally required.

When the centerline of the construction has been located, measurements are taken in the field from which the required quantities of cut or fill can be computed. A crosssectional view of the land is plotted from these measurements. The cross sections are taken on vertical planes at right angles to the centerline. Where the ground surface is regular, cross sections are taken at every full station (100 feet), Where the ground is irregular, they must be taken at intermediate points as determined by the surveyor. A typical cross section is shown in Figure 3-4.

sides of the bases               are crossed by a line perpendicular to each, the distance between the two bases along this perpendicular line is the altitude       of the trapezoid. The area of any trapezoid can be expressed as the average length of the bases multiplied by the altitude. This relationship can be expressed by the formula:
Basic Formulas. Before the area of the cross section can be computed, the basic formulas for the computation of the areas of triangles and trapezoids must be understood.

If a line is drawn, as shown in Figure 3-6, from one of the vertices of a triangle perpendicular to the side or base (b) opposite this vertex, the line formed represents the altitude (h) of the triangle. The area of any triangle can be expressed as the product of one-half the base multiplied by the altitude. This relationship is expressed by the formula:
Computation of Areas. The first step in computing areas by the trapezoidal method is to break the cross-sectional area into triangles and trapezoids by drawing verticals, as shown in Figure 3-5. Then determine the area of these small figures by the appropriate formula.

To determine the appropriate dimensions, the notes taken by the surveyors must be known. The cross-section notes taken in the field are in fractional form.

The figure below the line indicates the horizontal distance from the centerline to that point on the ground. The figure above the line indicates the ground elevation of that point.

Points on the grade line of the proposed road are written in a similar manner and are obtained by computations from the final grade line to be established, as shown in Figure 3-8.

Thus, the note 32.0/21 indicates a point that is at elevation 32.0 and
21 feet from the centerline of the road. If A trapezoid is a four-sided figure having two sides parallel but not equal in length, as shown in Figure 3-7. If the two parallel

## 3-8 Surveys And Earthwork Operations

the cross section is divided into triangles Stripper Method and trapezoids by erecting verticals, obtain The stripper method is a variation of the notes for the centerline, shoulders, and end trapezoidal method.

To use this method, of slopes to solve for the area.

consider a section such as that shown in Figure 3-9.

Example: If vertical lines are drawn at equal distances apart, then by the trapezoidal formula, the end area, A, will be given by the following computation:
To solve the triangles and trapezoids formed, consider the bases of these figures to be vertical and the altitudes to be horizontal. All vertical bases are found by subtracting elevations, and all horizontal altitudes are found by subtracting horizontal distances from the closest vertical in the direction of the centerline.

Factor in and combine terms:
Examples:
Referring to Figure 3-8, area a], and substituting in the formula for the area of a triangle:
First, measure (graphically) each length (b)
and multiply the sum by the width (w) (constant). The distance between vertical lines, w, may be any value, but it must be constant throughout the cross-section area. In rough terrain the vertical lines should be closer together to ensure greater accuracy.

Referring to Figure 3-8, area       and substituting in the formula for the area of a trapezoid:
Find the areas of the remaining trapezoid and triangle in the same way.

One of the easiest and most convenient ways to measure the vertical lines (b) is with a strip of paper or plastic. Lay the strip along each vertical line in such a manner as to add each in turn to the total.

The strip will show the sum of all vertical lines in the same scale that the cross section is plotted. This figure, multiplied by the value of w, will give the area of the cross section.

Double-Meridian Triangle Method The double-meridian method explained in Chapter 13 of TM 5-232 gives a more precise value for a cross-section area than the stripper method. However, it involves more time.

Inaccuracies result when either a triangle or trapezoid falls within the limits of w or when the area is curved. However, the method is rapid, and the accuracy is adequate under urgent conditions. Figure 3-10
shows a typical cross section with a stripper marked to show the total length of all vertical lines and the value of w. The stripper indicates that the sum of all vertical lines is 21.7 feet: w is given as 10 feet. Applying these figures to the formula, then-
With this method, shown in Figure 3-11, the area is subdivided into two series of trapezoids using the elevations of adjacent points and their projections on the centerline (the distances). These trapezoids have bases equal to the horizontal distance of the respective points from the centerline, and heights equal to their differences in elevation. Where the difference in elevation is plus, the area of the trapezoid is plus;
where the difference is minus, the area of the trapezoid is minus. The component areas are added algebraically. Because this procedure uses the sum of the bases of the trapezoid, the area obtained is double the true area and must be divided by 2. The computation is simple arithmetic: subtract adjoining elevations, multiply by the distance from the centerline, add the multiplied results and list plus and minus quantities, add these quantities, and divide by 2.

The steps for completing the procedure for the double-meridian triangle method follow
(refer to Figure 3-11).

tance from the centerline. Point (F) to point (A) is not considered because the sum of their distances from the centerline is zero. Going from a lower to a higher elevation gives a plus quantity, while going from a higher to a lower elevation gives a minus quantity. Place plus quantities in one column and minus quantities in another.

1. Start at the centerline ground or grade elevation, whichever is lower (A). Work from the centerline in a clockwise direction to the left (A), (B), (C), (D), (E), (F); and counterclockwise to the right (A), (G), (H),
(I), (F), to the centerline ground or grade elevation, whichever is higher (F).

3. Divide the algebraic sum of the plus and minus quantities by 2 to obtain the area of the cross section in square feet (sq ft). In sections having both cut and fill, treat each part as a separate section.

2. Working from point to point, multiply the difference in elevation between each adjacent pair of points by the sum of their dis-

## Planimeter Method

Before measuring a specific area, determine the scale of the plot and set the adjustable arm of the planimeter according to the chart in the planimeter case. Check the setting by carefully tracing a known area, such as five large squares on the crosssection paper, and verifying the reading on the disk, drum, and vernier. If the reading is inconsistent with the known area, readjust the arm settings until a satisfactory reading is obtained.

A polar planimeter is an instrument used to measure the area of a plotted figure by tracing its perimeter. The planimeter, shown in Figure 3-12, touches the paper at three points: the anchor point, P; the tracing point, T; and the roller, R. The adjustable arm, A, is graduated to permit adjustment to the scale of the plot. This adjustment provides a direct ratio between the area traced by the tracing point and the revolutions of the roller. As the tracing point is moved over the paper, the drum, D, and the disk, F, revolve. The disk records the revolutions of the roller in units of tenths;
the drum, in hundredths; and the vernier, V, in thousandths.

NOTE: Always measure cut and fill areas separately.

To measure an area, set the anchor point of the adjusted planimeter at a convenient position outside the plotted area. Place the tracing point on a selected point on the perimeter of the cross section. Take an initial reading from the disk, drum, and vernier. Continue by tracing the perimeter clockwise, keeping the tracing point carefully on the lines being followed. When the tracing point closes on the initial point, take a reading again from the disk, drum, and vernier. The difference between the initial reading and the final reading gives a value proportional to the area being measured.

Check the accuracy of the planimeter as a measuring device to avoid errors from temperature changes and other noncompensating factors.

A simple method of testing its consistency is to trace an area of 1
square inch with the arm set for a 1:1 ratio. The disk, drum, and vernier combined should read 1.000 for this area.

Make two independent measurements to ensure accurate results.

The first is performed as discussed above. The second measurement is made with the anchor point again placed outside the area being measured but on the opposite side of the area from its position in the first measurement. This procedure gives two compensating readings the mean of which is more accurate than either.

In either form, the formula is only accurate when A1 and A2 are approximately the same shape. The greater the difference in shape between the two end sections, the greater the possibility of error. However, the method is consistent with field methods in general.

In most cases, the time required for a more accurate method is not justified.

Prismoidal-Formula Method To measure plotted areas larger than the capacity of the planimeter, divide the area into sections and measure each section separately, as outlined above.

## Computer-Aided Design (Cad)

Very accurate measurements can be made if cross sections arc digitized using CAD.

Cross sections can be placed on a digitizing pad, points plotted into the computer and, with one command, the area calculated, The prismoidal method is used where either the end areas differ widely in shape or a more exact method of computing volume is needed.

Its use is very limited because it requires more time than the average-endarea method and gives greater accuracy than is required for most road and airfield construction.

The prismoidal formula is

## Methods Of Volume Determination

where
An engineer can accomplish the necessary earthwork computations by using the following methods:
average- end-area, prismoidal formula, average-depth -of-cut-or-fill, grid, or contour.

## Average-End-Area Method

The average-cnd-area method is most commonly used to determine the volume bounding two cross sections or end areas.

use the formula:
Determine    by averaging the corresponding linear dimensions of        and then determining its area, rather than averaging the areas of Average-Depth-of-Cut-or-Fill Method where
V is the volume, in cubic yards (cy) (1 cy =
27 cubic feet (cf)), of the prismoid between cross sections having areas in square feet of A1 and A2, separated by a distance of L
feet .

With only the centerline profile and final grade established, earthwork can be estimated with the average-depth-of-cut-or-fill method. Estimate the average depth of cut or fill between 100-foot stations and obtain the volume of material from Table 3-1, page
3-14, The accuracy of this method depends on the care given to establishing the centerline profile, the instruments used, and the accuracy of field reconnaissance.

If cross sections are taken at full 100-foot stations, the volume in cubic yards between successive cross sections           in square feet, may be found by the formula:
This table shows the number of cubic yards of earthwork that are in a 100-foot-long section of cut or fill having a known average depth. To use this table you must know the following:

1. Width.
a. Cut section - the width of the base of the cut, including ditches.
b. Fill section - the width of the top of the fill.
2. Average amount of cut or fill.
3. Slope ratio. Column 2 gives the correct amount of earthwork when the side slopes are 1:1. When the slope ratio is other than 1:1, an adjustment must be made (see column 4).

NOTE: The final answer obtained from the table is for a section 100 feet long. If the actual length of the cut or fill is not 100 feet, an adjustment must be made. (For an 85-foot section, multiply by 0.85; for a 50-foot section, multiply by 0.50, and so on.)
However, the volumes obtained by this method are generally adequate for most military construction.

earthwork quantities for airfields should be estimated mainly from cross sections. However, in the absence of sufficient time, the average-cut-or -fill method is better than none at all.

Determine the following before using Table
3-1:
- Average amount of cut or fill.

The centerline profile of a road is typical of the entire transverse section because of the narrow widths. Because of the greater width required on an airfield runway, the cen terline profile may be misleading as to the typical conditions across the entire transverse width at that point. Therefore,

- Width of the base of the cut or the top
of the fill in 2-foot increments between
26 feet and 44 feet.
squares must be of such size that no significant breaks, either in the original ground surface or in the pit floor, exist between the corners of the square or between the edges of the excavation and the nearest interior corner.

- Quantity to be added to the figure in
column 2, if the width of the base or top
of the fill is an odd number of feet.
Z Quantity to be added if the slope ratio
on both sides is 1.5:1 or 2:1.
NOTE: The table is based upon a length of 100 feet between cross sections and a slope ratio of 1:1.

Follow these steps to use the table:
By taking elevation readings at the stakes before and after excavation, data is obtained to compute the volume of borrow taken from the pit.

Figure 3-13 shows a borrow pit over which 25 squares were staked, To identify the various intersecting points, label lines in one direction by numbers and in 'the other direction by letters. Thus the intersection of lines C and 3 would be labeled C3.

1. Enter column 1 and read down to the average amount of cut or fill for the length concerned.

Outline squares falling completely within the excavation with a heavy line, Within that line, determine the volume of excavation for each square in the following manner:
2. Read horizontally to the right and obtain the figure under the appropriate base of the cut or top of the fill in column 2.

1.  Label the points on one square, as shown in Figure 3-14, page 3-16,
3. Make corrections to this figure from columns 3 and 4, if they apply.

4. If the length is not 100 feet between the points considered, adjust the answer proportionately,

## Grid Method

When the quantity of material within the limits of the cut sections is not enough to balance the fill sections, material must be borrowed. The most convenient method is to widen the cuts adjacent to the fills where the material is needed. Compute the volume by extending the cross sections.

However, where this is not possible, locate borrow pits at some other area. The grid method is a convenient method of computing the borrow material available in a given borrow pit.

In this method, first stake out over the area a system of squares referenced to points outside the limits of work. The dimensions of these squares depend on the roughness of the original terrain, the anticipated roughness of the final surface, and the accuracy desired. Rougher terrain requires smaller dimensions to get accurate results. The
2. Points a, b, c, and d are on the original ground line, while            and    are on the final ground line. The volume of the

an hq. (Refer to Figure 3-13, page 3-15 and Figure 3-14.) The total borrow-pit quantity also includes the wedge-shaped volumes lying between the complete solids and the limits of excavation. For these volumes, use proportional surface areas, Use the formula: A grid is illustrated in Figure 3-15. The length of the sides of each square is 50
feet. Therefore, given
An alternative method is to compute the total of all cuts at each corner (123 feet), compute the average cut across all squares
(123/25 = 4.92), and then multiply by the length of the sides of the figure.

resulting form is the product of the right cross-sectional area A and the average of the four corner heights                           and
     in cubic yards.

3. The volume represented by each square might be computed by the preceding method and all volumes added. However, when a number of such volumes adjoin one another, it is quicker to use the following relation which gives the total volume, represented by all complete squares:
This could be approximated by adding all corner cuts and multiplying by A, or In the preceding formula, A is the right cross-sectional area of one rectangular solid,      is a corner height found in one solid,      is a corner height common to two solids,      is a corner height common to three solids, and      is a corner height common to four solids. As an example,     is

## Factors Influencing Earthwork Calculations

Loose and swell refer to a condition which is the reverse of shrinkage. The earth assumes a larger volume than its natural state when stockpiled or loaded into a truck. This factor ranges from 10 to 40 percent swell and is usually uniform for a given material.

On many projects, one objective of the paper location study is to design the grade line so the total cut within the limits of the work equals the total fill. The uncertain change of volume of the material make this difficult. It is usually more economical to haul excavated material to the embankment sections, thereby eliminating borrow and waste.

## Shrinkage

Shrinkage, however, varies with changes in the soil constituents and with changes in moisture content and the type of equipment used. Consequently, a percentage allowance assumed in design may eventually prove to be 5 percent or more in error. A
common shrinkage allowance is 10 to 30
percent for ordinary earth. Settlement refers to subsidence of the completed embankment.

It is due to slow additional compaction under traffic and to gradual plastic flow of the foundation material beneath the embankment.

Shrinkage has occurred when 1 cubic yard of earth, as measured in place before excavation, occupies less than 1 cubic yard of space when excavated, hauled to an embankment, and compacted. This difference is due to the combined effects of the loss of material during hauling and compaction to a greater-than-original density by the heavy equipment used in making the embankment.

## Net Volume Calculation

Shrinkage is small in granular materials such as sand and gravel, and is large in ordinary earth containing appreciable percentages of silt, loam, or clay.

in-
Shrinkage is very high (possibly 70 percent)
for shallow cuts containing humus, which is discarded as unsuitable for embankments.

These shallow cuts (usually 4 to 8 inches deep) arc called stripping.

Compute the volume of cut and fill and the net volume between any two points on the construction project.

The net volume is the difference between the volume of cut and the volume of fill between any two specified stations.

The net volume may apply to the entire project or to a few stations. Net volume may be described in a compacted, place, or loose state. Table 3-2 provides conversion factors used to find the net volume. All calculations are recorded on the earthwork volume sheet shown in Table 3-3.

## Earthwork Volume Sheet

This layer varies in depth but is usually 4
to 6 inches deep.

This material must be wasted because it is not satisfactory to place in an embankment, Indicate in column 6 the volume between stations of this humus material over sections of cut.

The earthwork volume sheets allow you to systematically record this information and make the neccessary calculations. They provide a means of tabulating earthwork quantities for use in the mass diagram discussed later in this chapter. The earthwork volume calculation sheet, shown in Table
3-3, is divided into columns for recording and calculating information.

Stripping Volume in Fill (column 7). Before an embankment can be constructed, the same layer of humus must be removed and the volume replaced with satisfactory material.

Indicate in column 7 the volume of this material between stations over sections of fill.

Stations (column 1). List in column 1 all stations at which cross-sectional areas have been plotted. Normally, these areas are taken at all full stations and at intermediate stations that are required to fully represent the actual ground conditions and earthwork involved.

Net Volume of Cut (column 8). Indicate in column 8 the volume of cut material between stations that is available for embankment. Column 8 is column 4 minus column 6, because the total cut must be decreased by the amount of material wasted in stripping, including the organic material.

Area of Cut (column 2). Record in column 2
the computed cross-sectional areas of cut at each station. These areas may be computed by one of the commonly used methods, depending on the degree of accuracy required.

Area of Fill (column 3), Complete column 3
in the same manner as column 2, except show cross-sectional areas of fill.

Volume of Cut (column 4). Complete the volume of cut material between adjacent stations and record it in column 4. The most common method for computing volumes is the average-end-area method (or the earthwork table based on this method).

Adjusted Volume of Cut (column 9). One cubic yard of material in its natural, undisturbed state occupies approximately 1.25
cubic yards when removed and placed in a truck or stockpile.

The same 1 cubic yard, when placed in an embankment section and compacted, occupies a volume of approximately 0.9 cubic yards. In planning operations, convert these various volumes to the same state so the comparisons can be made, Changes in volume of earthwork are discussed in this chapter, and Table
3-1, page 3-14, provides the necessary conversion factors. Column 9 is column 8 multiplied by the appropriate conversion factor
(in this case, 0.9) to convert it from inplace yardage to compacted yardage.

This volume represents only the volume of cut between the stations and the volumes reflected as in-place yardage. Volume of Fill (column 5). Complete column
5 in the same manner as column 4, except show fill volumes. Fill volumes reflect com-
Total Volume of Fill (column 10). Indicate in column 10 the amount of compacted material required between stations to complete needed embankments, Column 10 is column 5 plus column 7, plus the amount necessary to replace the quantity removed by stripping. This figure represents the fill material that is available (plus) or required tion 0 + 00. While passing through a
(negative) within the station increment after stretch where cutting predominates, this the intrastation balancing has been done.

column increases in value. While passing Mass Ordinate (column 12). Column 12 indithrough a stretch where embankment is required, this column decreases.

cates the total of column 11 starting at sta-

## The Mass Diagram

The first step in planning earthmoving plans for economical and efficient compleoperations is the estimation of earthwork tion of the earthmoving mission.

quantities involved in a project. This can be done accurately by one of several The mass diagram is one method of analyzmethods, depending upon the standard of ing earthmoving operations. This diagram construction preferred. With these escan tell the engineer where to use certain timates, the engineer can prepare detailed types of equipment, the quantities of materials needed, the average haul total volume for the cut at station A to B is obtained by projecting the points on the curve line at stations A and B to the vertical axis and reading the volume distanccs and, when combined with a ground profile, the average slope for each operation. This permits the preparation of detailed management plans for the entire project. The mass diagram is not the complete answer to job planning, and it has limitations that restrict its effectiveness for certain typres of projects. However, it is one of the most effective engineer tools and is easily and rapidly prepared.

## Construction Of The Mass Diagram

Conversely, if at one station more material is being filled than cut, you have a fill operation at that station. The quantity or volume of deficient material will be increasing as filling operations continue through the station, producing a descending massdiagram curve line. Filling is occurring from stations B to D in Figure 3-17. The total volume for the fill at stations B to D is obtained by projecting the points on the curve line at stations B and C to the vertical axis and reading and adding the volumes above and below the zero datum line.

Using column 1 (station) and column 12
(mass ordinate, cumulative total) of a completed earthwork volume sheet, a mass diagram can be plotted as shown in Figure
3-16.

The maximum or minimum point on the mass diagram, where the curve changes from rising to falling or vice versa, indicates a change from cut to fill or vice versa. This point is referred to as a transition point
(TP). On the ground profile, the grade line crosses the ground line at the TP, as illustrated at stations B and D.

Plot the mass diagram on scaled graph paper with the stations indicated horizontally and the mass indices (column 12) denoted vertically. Connect all plotted points to complete the mass diagram as shown in Figure 3-16. Positive numbers arc plotted above the zero datum line, negative numbers below.

## Properties Of The Mass Diagram

Figure 3-17 shows a typical mass diagram with the actual ground profile and final grade line of the project plotted. Note that both usc the same horizontal axis (stations).

The ground profile is placed above the mass diagram to facilitate the calculation of the average grade over which equipment will work. The horizontal axis is the only thing these graphs have in common.

When the mass diagram crosses the datum line or zero volume, as at station C, there is exactly as much material filled as there is material cut, or zero volume excess or deficit at that point. The section of the mass diagram, from the start of the project at station A to a point of crossing the zero volume line, is known as a *node.* Each crossing point on the zero volume line indicates another node. The last node may or may not return to the zero datum line. Nodes are numbered from left to right. The final position of the mass diagram line, above or below the datum line, indicates whether the project was predominately cut or fill. In Figure 3-17, where the mass diagram ends at station E, the operation was cutting; that is, surplus material was generated by cutting and must be hauled away (waste operation). Borrow operations occur when the final position of the mass diagram is below the zero volume line.

The mass diagram is a running total of the quantity of earth that is in surplus or deficient along the construction profile. If at one station more material is being cut than filled, you have a cut operation at that station. The quantity or *volume* of surplus material will be increasing as cutting operations continue through the station, producing an ascending mass diagram curve line.

Cutting is occurring from stations A to B
and stations D to E in Figure 3-17. The

## Project Analysis

These lengths are measured using the horizontal scale (stations measured in hundreds of feet).

Always use the maximum haul distance (length) of each piece of equipment, provided the project or node is at least that length.

Start excavating each node with the dozer followed by the scraper and dump truck.

Figure 3-18 shows a balance line drawn on a portion of a mass diagram. If this was a dozer balance line, the distance between stations A and C would be 300 feet.

Once the basic properties of the mass diagram arc understood, the engineer can conduct a detailed analysis 10 determine where dozers, scrapers, and clump trucks will operate This is accomplished by using balance lines. A balance line is a line of specific length drawn horizontally, intersecting the mass diagram in two places. The specific length of the balance line is the recommended working or maximum haul distance for different pieces of equipment. The term *maximum haul distance* is used because opera ting the equipment beyond this point would not be efficient. The maximum haul distances (balance-line lengths)
are

Maximum
Equipment
Haul Distance

Cut equals fill between the ends of a balance line. The mass line returns to exactly the same level, indicating that the input and the expenditures of earth have been equal. In Figure 3-18, this occurs between stations A and C. There has been an exact balance of earthwork.

Dozer
Up to 300 feet
Scraper
301 to 5,000 feet

In Figure 3-18, the amount of material made available by cutting between stations A and B is measured by the vertical line marked Q. This is also the amount of embankment material required between sta-

Dump Truck
5,001 feet to several
miles

tions B and C. This is described as the balanced quantity of earthwork.

If equipment was used to do the balanced earthwork between stations A and C, the maximum distance that earth would have to be moved would be the length of the balance line AC.

been drawn.

The same principles apply for the area between the lines as with only one balance line. The quantity balanced is the vertical distance between the balance line, while the horizontal bisector is the average haul distance.

The longer balance line is the maximum haul distance, and the shorter balance line is the minimum haul distance. The haul distance depends upon the position of the curve with respect to the balance lines.

In accomplishing balanced earthwork operation between stations A and C, some of the haul distance would be short, while some would approach the maximum haul distance. The *average haul distance* (AHD) is the length of the horizontal line placed midway between the balance line and the top or bottom point (transition point) of the curve (Figure 3-18) and is found by dividing the vertical distance of Q in half. If the curve is above a balance line, the direction of haul is from left to right. The converse is true when the curve is below a balance line.

Figure 3-19 shows a part of a mass diagram on which two balance lines have The mass diagram is a useful indicator of the amount of work expended on a project. By definition, *work* is the energy expended in moving a specified weight a given distance.

It is the product of weight times distance. Because the ordinate of the mass diagram is in cubic yards (which represents weight) and the abscissa is in stations or distance, an area on the mass diagram represents work. In Figure 3-20, page 3-24, if equipment is used to do the balanced earthwork between the ends of the balance lines as drawn, the work expended is equal to the area between the mass line and the balance line.

at haul distances that are within its best range of efficiency.

Figure 3-21 illustrates a portion of a mass diagram on which two balance lines have been drawn: 300 feet to conform to dozer capabilities and 5,000 feet for the scraper.

Another item calculated from the mass diagram is average grade. This value is used when computing equipment scheduling and utilization.

Figure 3-21 and Figure
3-22, page 3-26, illustrate a portion of the mass diagram on which the average grade has been determined.

The following job analysis can be made from the diagram in Figure 3-21:

## Use Of The Mass Diagram

Use dozers between stations C and E. The maximum haul distance is 300 feet; the average haul distance is the horizontal bisector shown. The amount that will be cut between stations C and D and filled between stations D and E is the length of the indicated vertical lines.

The mass diagram is used to find the cost of a project in terms of haul distance and yardage, to locate the areas for operation for various types of equipment, to establish the requirements for borrow pits and waste areas, and to provide an overall control of required earthmoving operations. However, the means used to analyze the mass diagram will follow the same principles regardless of the end result desired. The analysis of the mass diagram is based upon the proper location of balance lines.

Use scrapers for cutting from stations A to C and filling from stations E to G. The minimum and maximum haul distances are
301 and 5,000 feet, respectively. The average haul distance is the horizontal line midway between the balance lines. The amount of earthwork is indicated by the vertical line.

To determine the average grade for either the scraper or dozer work area, use the following procedure:
Because the lengths of balance lines on a mass diagram are equal to the maximum or minimum haul distances for the balanced earthmoving operation between their end points, they should be drawn to conform to the capabilities of the available equipment. Equipment planned accordingly will operate

## 3-24 Surveys And Earthwork Operations

5. Calculate the average grade as follows:
Average Grade % =
1. Draw on the profile a horizontal line through the work area that roughly divides the area in half. This is a rough estimation. (See Figure 3-22, page 3-26.)
In the example shown in Figure 3-23, the average grade for the dozer would be
2. Extend a vertical line from the end points of the previously determined average haul line up through the project profile.

These lines are referred to as the average haul vertical. (See Figure 3-23, page 3-26.)

Average $\bf{C}$

$\bf{18}^{\rm{"}}$

$\bf{203}^{\rm{"}}$

$\bf{x}$

$\bf{100}$

$\bf{-8.875}$
3. Draw a final line connecting the intersecting points of the lines drawn in steps 1
and 2. This line represents the average grade.

4. Determine the average change in elevation (the vertical distance between the cut and fill).

Since this is an operation which moves earth *downhill,* the grade would be negative, or -8.87% An uphill cut would have a positive grade.

## Placement Of Balance Lines To Minimize Work

If there is an even number of adjacent
nodes, as shown in Figure 3-25, work is
reduced when the balance lines are one con-
tinuous line and AB + CD + EF = BC + DE
+ FG. The length of each balance line must
be within equipment maximum haul
capabilities as defined earlier.

Because the area between the apex of the
mass diagram and the balance line is a
measure of the work involved in the balanc-
ing operation, the size of these areas
should be decreased whenever possible,
However, the method used to minimize the
area depends upon the shape of the mass
diagram and the number of adjacent nodes
that can be used.

If two nodes are adjacent, work is mini-
mized when two balance lines are drawn as
one continuous line, with the balance lines
equal in length.
                 Each balance line must be
within the maximum efficient haul distan-
ces for the equipment. The best placement
of balance lines on the portion of a mass
diagram shown in Figure 3-24 would be
lines AE and EF, with AE = EF.

If there is an odd number of adjacent
nodes, as shown in Figure 3-26, work is
decreased when the balance lines are one
continuous line and AB + CD + EF - (BC +
DE) equals the limit of efficient haul, or ap-
proximately 1,000 feet. All balance lines
must be within equipment limits.

Only one balance line, CH, may be needed
if it is within efficient haul distance
specifications. The quantity involved would
be Q yards and the work involved would be
the area above CH.

## Calculation Of Earthwork Not Within Balance Lines

If this one balance line was replaced by two
balance lines, BD and DG, with BD less
than DG. the quantity of earthwork
balanced would remain the same. The
work would be decreased by the size of the
area between CH and DG and increased by
the size of the area between BD and C.
This would result in a savings because the
increase is less than the decrease for the
same amount of earthwork balanced. This
decreasing process will continue by raising
the lines to the point where one equals the
other, or until AE = EF is reached.

It is usually impossible to place balance
lines so that the entire amount of
earthwork on a project can be balanced.
Some part of the mass line will be outside
the balance lines. This material must be
wasted or borrowed. If the portion not
within balance lines is ascending (cutting),
there is waste; if it is descending (filling),
there is borrow,
                  This is shown in Figure
3-27, page 3-28.
                  Concentrate all necessary
borrow and waste operations in one general
area.

## Limitations Of The Mass Diagram

The mass diagram has many limitations that preclude its use in all earthmoving operations. At best, it is merely a guide indicating the general manner in which the operations should be controlled. Any attempt to get exact quantities and distances from it may be misleading. However, it is a good starting point.

Format for Analysis The mass diagram is most effective when used to plan operations along an elongated project similar to a road, an airfield runway, or a taxiway. The haul distances are along the centerline or parallel to it.

However, if the project becomes relatively wide compared to its length, movement of earth may be transverse as longitudinal, resulting in longer, transverse haul distances and invalidating the mass diagram analysis.

The simplest and most practical method of Tabulating the results of a mass diagram is to write all quantities and distances on the diagram, as shown in Figure 3-28. It is also possible to extract information from the mass diagram and put it in a format that effectively controls the operation. One method is to prepare a mass diagram analysis sheet as shown in Figure 3-29.

The mass diagram is used to analyze only the potentiality of balancing within one tions.

This is not necessarily true. However, all unacceptable quantities can be eliminated from the earthwork table.

phase of a project.

For instance, the mass diagram may indicate that the best balancing of a certain portion of a runway will require a haul distance of 2,200 feet along the site. However, it may be better to balance yardage with an adjacent taxiway in which the haul distance will be only
1,200 feet. The mass diagram can deal only with the runway or the taxiway, not with both simultaneously.

The mass diagram is applicable to projects needing balanced earthwork. Balancing eliminates the double handling of quantities. If there is a short distance between an acceptable borrow pit and an embankment section, it may be more economical to use the borrow pit instead of a long balancing operation, This can be determined by a work or economy. study.

The mass diagram assumes that all material excavated in the cut sections is acceptable for use in the embankment sec-

Clearing, Grubbing, and Stripping Forest Types and Environmental Conditions
                                                                                       Preparation
                                                                                                                  Clearing Considerations
                                                                                                                                                              Performance Techniques

4

## Clearing, Grubbing, And Stripping

Land clearing is the removal and disposal of all vegetation,
rubbish, and surface boulders embedded in the ground. In the
TO, land clearing also includes the removal and disposal of
mines, booby traps, and unexploded bombs. Grubbing is the
uprooting and removal of roots and stumps. Stripping is the
removal and disposal of unwanted topsoil and sod.

Clearing, grubbing, and stripping are accomplished by using
heavy engineering equipment.
                              Hand- or power-felling equip-
ment, explosives, and fire are also used. Factors that determine
which method to use are: the acreage to be cleared the type
and density of vegetation, the terrain's effect on the operation
of equipment, the availability of equipment and personnel, and
the time available for completion. For best results, a combina-
tion of methods is used in a sequence of operations.

Clearing, grubbing, and stripping are the same in road and
airfield construction.
                    In airfield construction, the areas to be
cleared are usually larger than for road construction; the number
of personnel and amount of equipment used are correspondingly
greater; and the disposal of unsuitable materials requires more
detailed planning and longer hauls.

## Forest Types And Environmental Conditions

the forests in an area can guide detailed reconnaissance.

The climate classifications of forests are temperate, rain, monsoon, and dry, The following paragraphs describe these classifications.

Clearing, grubbing, and stripping operations differ in every climatic zone because each zone has different forest and vegetative types. Forests are not uniform in type, growth, and density within climatic zones.

Soils, altitudes, water tables, and other factors vary widely within each zone.

## Temperate Forests

The general nature of a forest is determined from records of the principal climatic factors, precipitation, humidity, temperature, sunlight, and the direction of the prevailing winds. The nature and action of climatic factors during the growing season determine the amount and types of forests. From these records, a general interpretation of Temperate forests contain both softwood and hardwood trees. Hardwoods are dominant where the soils are old, deep, and fertile. Softwoods are dominant where the soils are young, shallow, and less fertile.

The density of growth in these forests varies with topography and local climate conditions.

Bogs are common in cold region, softwood forests. Bogs present a hazard to construction equipment during the clearing operations. Root systems vary according to geologic conditions and species. The types of root systems typical of various species are listed in Table 4-1.

tered growths of low, thorny, stunted shrubs and stunted trees that usually have long, tough taproots that are difficult to remove. Savanna forests are in more humid, dry-forest regions. These forests are park-like, with large trees widely and uniformly spaced. Savannas usually have continuous coverings of small grasses.

## Rain Forests Geologic And Permafrost Conditions

An investigation of the geologic conditions of a forest can help when estimating the density and depth of the root systems of the trees.

The investigation should be concerned with hardpan, marshy, and permafrost conditions. Hardpan or Rock Rain forests occur in tropical climates where rainfall is heavy throughout the year. They consist of tall, broad-leaved trees that grow as high as 175 feet. The trees have an umbrella-like foliage that permits little sunlight to penetrate.

The undergrowth consists of thick vines that cling to the trees for support and grow to great heights.

Where sunlight reaches the forest floor, the undergrowth is dense and varied. Because of continual precipitation, the root systems are on or near the ground surface and spread in a lateral pattern around the base of the trees,

## Monsoon Forests

Where a forest is closely underlaid by hardpan or rock, the tree roots branch and remain near the surface.

This growth is easy to uproot.

Where the soil is firm and the hardpan or rock is deep, the trees tend to form large, deep taproots that make uprooting difficult. Inundated, Marshy, and Boggy Areas In these areas, trees have thick, widespreading. and shallow root systems near the surface of the ground.

Monsoon forests occur in climates of heavy seasonal rains with strong, warm winds.

The forests are dense, with varied species of hardwoods which are moderate-sized, broad -
leaved, and have shallow root systems. The undergrowth is very dense with shrubs, vines, and plants.

## Permafrost Dry Forests

the surface, trees In northern regions where permafrost occurs, the root systems of trees are similar to those in hardpan or rock. Where the permafrost is near the surface, roots branch out and lie close to the surface.

Where permafrost is far below develop taproots.

Dry forests occur in arid and tropical regions where there is little precipitation. The forests are either scrub or savanna.

Scrub forests usually consist of broadleaved hardwoods with dense thickets along watercourses. In open areas there are scat-

## Preparation Reconnaissance And Planning Intelligence Reports,

and aerial and ground reconnaissance.

(Refer to Chapter 2 of this The types of trees, vegetation, soil, and termanual for more detailed in formation.)
rain encountered while clearing the land After such information has been verified, esmust be determined as accurately as postimate the quantity of work, select the availsible from climatic and geological maps, able equipment, determine the number of

## 4-2 Clearing, Grubbing, And Stripping

work required in clearing. A sample, usually 10 percent of the area, is studied and the result is applied to the entire area. The sample may be increased or decreased. In small areas, a 100-percent cruise is usually made.

personnel needed, and plan a sequence of operations to complete the clearing rapidly and efficiently. In all clearing operations, the decisive factors controlling the method of clearing are the type and amount of equipment and the time available for completion.

## Timber Cruising

In timber cruising for land clearing only, record the diameters of the trees at breast height (DBH) taken at 4 1/2 feet above the ground, and record the species and number of trees. This information is used to plan the clearing operation and select the type of equipment most efficient for the diameters and species.

Timber cruising is performed to estimate the size, the height, and the number of each tree species in a given area. It is used either to determine the quantity of usable timber or to estimate the amount of

## Clearing Considerations Camouflage Permafrost

Clearing of ground cover over permafrost which is near the freezing point may result in thawing of material, causing considerable ground-surface subsidence.

## Safety

To provide cover and concealment
(camouflage) for the construction site, do not remove standing trees and brush outside the designated cleared area unless necessary.

When uprooting trees with bulldozers, take care to control their fall and avoid breaking surrounding trees.

## Timber Salvage

Trim all timber useful for logs, piles, and lumber, and stockpile it for future use in bridge, culvert, and other construction applications.

Push or skid this timber into a salvage area where it can be moved to a sawmill with little difficulty.

Careful consideration must be given to the safety of personnel and equipment during clearing operations. Protective, tractormounted cabs should be used when extensive clearing operations are anticipated.

Protective cabs permit greater flexibility in clearing operations and increase operator efficiency. With this protection, damage to the dozer is reduced and continuous production results.

## Temporary Drainage

for protection of the unwill prevent stumps, from damaging vulparts.

Proper supervision and planning can help prevent accidents caused by falling trees, uprooted stumps, stump holes, and rough or broken terrain during the clearing operation. All equipment used in clearing should, if practicable, be equipped with heavy steel plating dercarriages. This logs, and boulders nerable equipment Phased development of the drainage system in the early stages of clearing, grubbing, and stripping is essential to ensure uninterrupted construction. Delays caused by flooding, subgrade failures, heavy mud conditions, and the subsequent immobilization of construction equipment can be eliminated by careful development of the drainage system before, or concurrent with, other construction.

Use the original drainage features as much as possible without disturbing natural grades. Grade drainage ditches downhill.

possible to shorten the hauling distance, Use the same methods to clear disposal areas that arc used in clearing work areas.

## Revetments

Cleared material can be disposed of by using it as fill material in revetments around hardstands when protective measures are needed.

## Burning

Fill holes left by uprooted trees and stumps with acceptable soil, and compact the ground to prevent the accumulation of surface water.

Use dozers and graders for this work. Slope the ground toward drainage ditches to prevent pending on the surface.

Backfill existing ditches at the latest possible time to permit the best use of the original drainage.

## Disposal

Do not use fire for clearing land unless suitable equipment and sufficient personnel are not available for other methods of clearing. When burning is required, closely follow recommended procedures.

Under favorable tactical conditions, brush and timber debris may be burned. To limit the likelihood of detection because of smoke, keep fires burning as hot as possible and do not push new material into the fire rapidly. Do not permit fires to burn at night unless tactical conditions are extremely favorable and approval has been obtained from headquarters.

Use waste areas or burning to dispose of cleared materials. The choice of method depends on the type of construction, environmental concerns, the location, the threat, and the time available. Generally, the material is pushed and skidded off the construction site and into the surrounding timber to speed disposal and keep the area cleared for equipment operation. To dispose of material as rapidly as possible, assign specific units of equipment to accomplish this concurrently with the clearing and grubbing.

The disposal method should be consistent with the methods of camouflage, salvage, and drainage clearing.

used for

## Waste Areas

In airfield construction, consideration must be given to the areas used for disposal of construction waste.

Fire Control. Strip the area around any debris to be burned before fires are started to provide a firebreak. If large areas are to be burned, establish firebreaks on all sides as a precaution against shifting winds.

Maintain a fire guard over the fires as an additional safety measure. In dry weather, hand shovels, water buckets, and other expedient fire-fighting equipment should be available to extinguish fires caused by flying sparks.

Dumps Adjacent to Work Areas debris can be piled without drainage or potential work In forward combat areas where saving time is essential, the quickest and most convenient method of material disposal is to pile the materials adjacent to the work area. Study the construction plans to determine where the interfering with areas.

## Off-Site Areas

In constructing Burning Pits. The most satisfactory method for burning large quantities of brush and timber is to burn them in a pit or trench dug by a bulldozer or scraper. The sides of the pit will reflect the heat back into the fire, producing a very hot fire, Burning will be rapid and complete. Push the material into the pit with a bulldozer. Start the fire with limbs and small brush to get a good bed of coals. Gradually increase the size of the material as the intensity of the fire increases. Get as little dirt as possible in the pit because it tends to smother the fire and fill the pit.

A soldier should be detailed to the main project, it may be necessary to clear some adjacent land to dispose of the cleared material. Locate this clearing as close to the main project as damage from tractor grousers and bulldozer blades.

tend the fire and ensure that the pile is kept compact, This method cannot be used in swampy areas where groundwater will seep into the trench.

Log Piles.

If it is not desirable to construct burning pits, burn piles of logs by loosely piling them so that the heat and flames can pass through, It is always best to start the fire with brush.

After a large bed of coals is formed, add a few logs at a time to obtain a good blaze.

Clearing and Piling Stumps. In preparing stumps for burning, remove as much dirt as possible from the roots. Dirt on the roots will retard combustion and smother the fire.

When the stumps are pushed out, leave them with the roots exposed to sun and wind so the dirt till dry quickly. Scrubbing with the side of the bulldozer blade will knock off much of the dry dirt.

Pile the stumps as close together as possible with the trunks pointing toward the center of the pile. Keep the stumps together after they start to burn. This procedure will speed up the burning.

## Airfield Approach Zones

To burn piles of green, wet logs, it may be necessary to use fuel oil to furnish enough heat to dry out the logs and start the burning process. Pile the logs parallel, one on top of the other.

The fuel oil is carried to the center of the pile by a pipe in which holes have been drilled or cut. Once the pile is burning well, the fuel can be cut off and the pipe removed. Care must be taken to avoid ground contamination. Fuel oil is also a quick and convenient means of starting brush fires, particularly if the brush is green and wet. If material is to be pushed onto the pile while the pipe is being used, it is best to bury the portion of the pipe outside the pile to protect it from Airfield glide angles and approach zones are further discussed in Chapter 11 of FM 5-430-00-2/AFPAM 32-8013, Vol 2. Obstructions extending above the glide angle must be removed. Although glide-angle requirements may be met by only topping trees, it is best to fell or uproot trees that extend above the glide angle. Disposal is no problem in the approach zone, because all demolished material is left in place.

## Performance Techniques Clearing With Equipment

quired for the job.

Clearing rates are discussed in FM 5-434. Limitations and applications for each type of equipment follow.

## Bulldozer

When clearing an area in dry or temperate forests, the bulldozer is the most efficient mechanical equipment for removing small brush, trees, and stumps up to 6 inches in diameter. Although more time and effort are required, bulldozers can also remove trees up to 30 inches in diameter when tractor-mounted clearing units and power saws are not available. Because of its ability to push, move, and skid felled trees and brush, the bulldozer is used extensively as the primary unit of equipment in all clearing operations.

The use of engineer equipment is the most rapid and efficient method of clearing. The use of such equipment is limited only by un usually large trees, stumps, and terrain that decrease the maneuverability of the equipment and increase maintenance requirements. This type of equipment includes bulldozers; tree-dozer, tractor -
mounted units; tractor -mounted clearing units; winches; power saws; rippers; and motor graders.

In addition, pioneer tools are used for some clearing operations.

Table 4-2 summarizes the limitations and proper applications of engineer equipment in clearing operations. Use production rates of equipment under normal operating conditions for determining the total time re-

## 4-6 Clearing, Grubbing, And Stripping

When clearing with bulldozers, the sequence of operations depends on the type of trees, the terrain, and planned construction. After establishing the boundaries of the clearing, select spoil areas for disposal of all cleared material based on the shortest haul, a downgrade slope, effective camouflage, and general accessibility.

each type where it is most effective. Use power saws, for example, to fell large trees.

Use clearing units to uproot large stumps and work in areas inaccessible to dozers.

Use bulldozers to clear, stockpile, and dispose of light material. The operational methods used by bulldozers in clearing depend on the size of the trees. The methods briefly discussed below are discussed fully in FM 5-434.

Start clearing at the disposal area and move in each direction away from it. Use one or two dozers to clear the small trees and brush only. Another pair of dozers will remove the larger trees and stumps bypassed by the previous units. If necessary, add more dozers for a third cycle of operation to take care of the heaviest removals.

Small Trees, 6 Inches or Less in Diameter, and Brush.

In clearing small trees and brush, operate the bulldozer with the blade straight and digging slightly. It may be necessary to back up occasionally to clear the blade. The cleared material can either be pushed into windrows for later removal or pushed off to one side of the area to be cleared.

Move the cleared material to the spoil area by skidding, pushing, or pulling. Disposal should be done with uprooting and removing. It is best to have a separate crew assigned for disposal.

Medium Trees, 6 to 12 Inches in Diameter.

To push over trees that range from 6 to 12
inches in diameter, set the blade of the bulldozer as high as possible to gain added leverage (Figure 4-1). As the tree falls, the Multiple operations are possible when other types of equipment are available, using

## 4-8 Clearing, Grubbing, And Stripping

However, if the tree has a large, deeply embedded root system, use the following method (Figure 4-2, page 4-10):
bulldozer is backed up quickly to clear the roots. With the blade lowered, the dozer travels forward again and digs the roots free by lifting the blade. The felled tree is then ready for removal to the spoil areas.

Step 1. Opposite the direction of fall, make a cut deep enough to cut some of the large roots. Use a V-ditch cut around the tree, tilted downward laterally toward the tree roots.

Step 2.

Cut side two.

Step 3. Cut side three.

Large Trees. Removing large trees (over 12
inches in diameter) is much sIower and more difficult than clearing brush and small trees.

First, gently and cautiously probe the tree for dead limbs that could fall and injure you. Then, position the blade high and center it for maximum leverage. Determine the direction of fall before pushing the tree over; the direction of lean, if any, is usually the direction of fall, If possible, push the tree over the same as you would a medium tree.

Step 4. To obtain greater pushing leverage, buld an earth ramp on the same side as the original cut.

Then push the tree over.

As the tree starts to fall, reverse the tractor quickly to get away from the rising root mass. After hole so that felling the tree, fill the stump edge shears them off at ground level. The water will not collect in it.

operator is protected by a steel canopy and a guide bar that controls the direction of roots on the fourth side may falling trees.

NOTE: The need to be cut also.

The tree-dozer is a simple and efficient Tree-Dozer, Tractor-Mounted Unit piece of equipment used for military land-
The tree-dozer, or Rome plow, is a tractor clearing operations.

It does not appreciably with a blade that *stings* and *slices* large disturb the soil. It provides
trees. A sharp projection on the left side of the blade splits the trees, while the cutting

## 4-10 Clearing, Grubbing, And Stripping

- Clear fields of fire and security around
cantonments, airfields, and other
facilities.
- Right-of-way clearance to desired
depths along roads and railroads, thereby reducing the enemy's capability of
ambush.
areas (200 to 400 feet wide) that can be cut from the outside toward the center in a counterclockwise direction. The cut material then slides off the trailing
(right) end of the tree-dozer mounting and leaves the uncut area free of fallen debris. The windrows are placed lengthwise on the borders of the areas.

Piling is done by sweeping with the treedozer mounting.

Sweep a blade width at a time. Work from the center of each area, at a right angle to the border (Figure 4-3).

Before committing a tractor equipped with the tree-dozer mounting, investigate the soil condition in the area of operation to determine if it will support the equipment. Use the tree-dozer mounting to make cuts through any kind of forest except heavy swampland. Shear trees at ground level, sweep them into piles or windrows, and dispose of them. One tractor equipped with a tree-dozer mounting can clear approximately 1 to 2 acres per hour, depending on the tree density and size.

Use one of the following clearing methods:

Z Another method is shown in Figure 4-4,
page 4-12. Again, long areas are laid out in 200- to 400-foot widths, but the cutting is done from the center toward the sides in a clockwise direction. This allows the cut material to fall toward
the center, which becomes the windrow site. The piling is done with the treedozer mounting, following the pattern outlined on the right side of Figure 4-4. When windrowing, the operator keeps
the cutting edge on the ground while pushing into the windrow and raises it
Z When the tractor can move forward almost continuously, it shears to ground
level anything in its path, Fast production can be obtained by laying out long
when backing away. This allows accumulated soil to sift away and lessens soil deposits in the windrow.

windrows should be on the contour, and the tractor should work from the uphill side and push downhill to the windrow.

- Where the vegetation is dense and
small, the highest production can be obtained by cutting and windrowing simultaneously. Work from left to right at a
- On extreme slopes, rapid production is
obtained by working in a semicircular pattern, from left to right, at approximately right angles to the windrow (Figure 4-5). If the terrain is steep, the
90-degree angle to the windrow, with the trailing edge of the tree-dozer working against the uncut material. This prevents cut material from sliding off the moldboard and allows the cut material to accumulate on the mold board.

The area of vegetation should be laid out as shown in Figure 4-6, with the operator working in patches, from inside to outside in a counterclockwise direction and at right angles to the windrows. Sweeping and piling the resulting debris can be accomplished much faster when tractors are used in teams traveling abreast.

Winches Towing winches mounted on tractor-dozer units or trucks are limited in use for clearing operations because of their small capacities in comparison with the tree- and stump-pulling units.

When the moldboard is filled, the operator should stop the tractor and deposit the cut material. The operator should then reverse to the starting point and repeat the operation to the right (Figure 4-6, page 4-14), reducing the time lost in backing up. When the tractor reaches the previously cut material, the operator should deposit cut material and form another windrow.

Tractor-Mounted Winch. Use tractormounted winches for uprooting trees and stumps up to 24 inches in diameter.

capacities are too limited for heavy work.

Their best use is for skidding felled trees and logs to a disposal area, if the haul road is sufficiently cleared for trucks to operate.

## Felling Equipment

hoisting and skidding felled trees, and extricating mired equipment. On the tractordozer unit, the winch is mounted in the rear and is directly geared to the rear power take-off on the tractor. The line pull developed varies with the size of the tractor, the speed at which the winch is operated, and the number of layers of rope on the drum. The line pull of a tractor-mounted winch is only about one-half the pull of a standard tree- and stump-pulling unit. Truck-Mounted Winch. As an expedient, truck-mounted winches can be used on trees up to 6 inches in diameter. Their Felling can be done with hand tools or power equipment.

Axes, two-man saws, shovels, pick-mattocks, and machetes are used to chop or saw down standing timber; dig and uproot stumps: and slash grass, vines, and undergrowth. Clearing by hand is usually too slow and difficult for military requirements unless explosives or mechanical methods are used. When labor is equipment. Refer to FM 5-250 for the correct application of explosives and demolitions.

plentiful, forests are dense, and terrain is rough, this method of clearing can be used with good results.

Power equipment and chain and circular saws are the principal ways of felling limber.

## Trees And Stumps Ripper

Methods of tree and stump blasting vary with the size and condition of the tree, root structure, and ground conditions, Figure
4-7, page 4-16, shows the methods of placing charges to blast stumps with different root structures.

Table 4-1, page 4-3, shows the type of root system for several tree species in temperate forests.

In land clearing, the ripper is used to help in the removal operations of bulldozers and tree- and stump-pulling units. The ripper cuts and breaks tree roots and loosens boulders from the ground. The short depth of shank penetration limits its use to shallow root systems. Prior to stripping operations, the ripper is used to loosen and break up frozen soil or organic material for easier removal by graders or scrapers.

The size of the charge required depends on the strength of the explosive available; the size, variety, and age of the tree or stump;
and soil conditions.

## Grader

The grader is used 10 cut grass and weeds, remove small brush, and clear the area of dead vegetation.

The terrain must be level and free from boulders and trees.

Used with rippers and bulldozers, graders can windrow the cleared material for later removal by other equipment. The grader is extremely limited in most clearing operations.

Various types of tools (such as pinch bars, earth augers, and spoons) can be used when drilling holes for the charge. Wood augers can be used for taproots. For loading and tamping, any smooth, wooden pole about 5 feet long and 1 1/2 inches in diameter can be used. The handle from a long-handled shovel is excellent because the crook of the blade end provides a good grip.

All holes must be tamped firmly with earth to retain the full force of the explosion.

## Clearing With Explosives Boulders

When boulders cannot be used in an embankment or fill, they must be removed from the construction area. Blasting is a quick and easy method of dislodging boulders.

Mudcapping, blockholing, or snakeholing (described in Chapter 3 of FM 5-250 or Chapter 6 of FM 5-34) may be used. Refer to Chapter 3 of TM 5-332 for quantities and types of explosives to be used and details regarding blasting rock.

## Removal Of Surface Rocks

Explosives may bc used to fell standing trees, uproot entire trees and stumps, and remove and dispose of large boulders. Explosives, however, have several disadvan -
tages. The sound of the explosive can travel farther than the sound of the construction equipment.

In loose soil, the initial charge may be entirely a expended in compacting the soil under a tree or stump, and a second charge may be required to remove it. Deep taproots often are only broken by explosives and have to be removed by hand.

Also, explosives generally take time to place and they create large craters, which require borrow excavation and compaction to backfill. In spite of these disadvantages, it is still sometimes necessary to use explosives to clear an area where the terrain precludes or seriously impedes the operation of heavy All surface rocks must be removed in certain types of construction. There are three methods used in this operation: hand, bulldozers, and cranes or scoop loaders with trucks.

The choice of method depends upon the situation.

## Hand

windrowed by dozers for later removal by scrapers or shovels and trucks. If the distance is short, they may be pushed by dozers to the designated disposal area.

## Cranes Or Scoop Loaders With Trucks

When there is sufficient time and personnel, rocks are picked up and loaded into hauling units by hand. This slow method is used in military construction only as an expedient.

## Bulldozer

Clearing surface rock by this method alone is possible, but it is slow. If the rocks are first windrowed or moved into piles by bulldozers or graders, the shovel will load the trucks quickly and efficiently. The The bulldozer is the most commonly used engineer equipment for moving rocks to a fill or disposal area. The rocks may be rocks can then be hauled long distances for disposal.

## Stripping

the traffic does not interfere with the approach or takeoff of aircraft. Do not destroy main paved highways and railroad lines because they may be required for ground operations.

It is desirable to have the airfield located near a good road or railroad so supplies may be readily transported to the site.

## Buildings

Buildings may be completely razed with explosives or heavy equipment, leaving no salvage. They may be razed in a manner to conserve usable material, or they may be relocated.

## Removal Of Buried Explosives

Stripping consists of removing and disposing of the topsoil and sod that cannot be used as a subgrade, foundation under a fill, or borrow material. Examples of this material are organic soils, humus, peat, and muck, Unsuitable soil must be removed to a depth at which compaction and thickness requirements are satisfied.

Stripping is done concurrently with clearing and grubbing by using bulldozers, graders, scrapers, and sometimes shovels, Good topsoil and sod should be stockpiled for later use on bare areas for dust or erosion control or for camouflage.

## Removal Of Structures

Mines, booby traps, unexploded ordnance (UXO), and other buried explosives must be located and removed or neutralized before any construction operations begin. Check all reports and data on an area to locate and identify explosives.

An airfield construction site may be acceptable except for obstructions such as houses, railroads, power lines, and other structures on the proposed site or near the operation of aircraft. The primary selection of a site always involves compromises, The survey party often selects a site where limited clearing of structures will be necessary before full-scale operations can take place.

## Power Lines

Establish the boundaries of the construction area first, then make a visual search of the most likely places for explosives. They are usually near existing structures, houses, and roads; in disturbed ground hollows where the earth has visibly settled;
and under stockpiles, pickets, or stakes placed in unnatural locations. If time allows, thoroughly investigate the area with mine detectors or by probing methods.

The safety of personnel and equipment is primary at all times during the removal of mines.

The speed of clearance is secon -
dary, Whenever possible, use trained explosive ordnance disposal (EOD) detachments, particularly when the size of bombs precludes detonation in place.

Power lines obstructing forward area construction or glide angles should be removed. In rare instances, the lines may be needed intact and a different approach to the airfield must be used. If the lines cross the runway, relocate them around the nearest end of the runway. As a last resort, underground installation may be used if armored underground cable or conduit is available that will adequately insulate the lines, In rear areas, power lines that are not in an approach zone or not high enough to extend into the glide angle when located in an approach zone may be marked with suitable warning lights.

The method of mine and UXO removal is a command decision. For minefield with booby traps or other antihandling devices, it is best to destroy the mines in place by explosives or mechanical means.

UXOs

## Roads And Railroads

may be disarmed by ordnance personnel and then manually removed from the area and disposed.

If ordnance personnel are not available, destroy the device in place.

In general, roads and railroads present no obstructions when located near airfields, if Surface mines or bomblets may be able to be filled and compacted with acceptable be pushed from an area by using a drag material, using dozers or graders. For addichain or dozer. If devices are destroyed in tional information, see FM 5-434.

place, all resulting holes and craters must

Subgrades and Base Courses
                                      Design Considerations
                                                                              Subgrades
                                                                                                    Select Materials and Subbase Courses
                                                                                                                                              Base Course

## Subgrades And Base Courses

This chapter discusses the functions of the subgrade, subbase,
and base courses and covers the selections of materials and
construction procedures.
                          Chapters 8 and 9 of this manual
discuss the determination of the base- and surface-course thick-
ness for roads. Chapters 11 and 12 of FM 5-430-00-2/AFPAM
32-8013, Vol 2, include similar information for all classes of
airfields and heliports as well as all commonly used types OJ
surface materials. Additional information on soils, compaction,
and California Bearing Ratio (CBR) requirements is contained
in Chapters 2, 6, and 10 of FM 5-410 and in Chapter 2 of FM
5-530.

## Design Considerations

less the materials are more readily available) and are not discussed in detail in this chapter.

## Flexible-Pavement Structure

Pavement structures may be rigid or flexible. In rigid pavements, the wearing surface is made of portland cement concrete.

A rigid pavement made of concrete will have great flexural strength, permitting it to act as a beam and allowing it to bridge over minor irregularities that may occur in the base or the subgrade upon which it rests.

All other types of pavements are classified as flexible. In a flexible pavement, any distortion or displacement occurring in the subgrade is reflected in the base course and continues upward into the surface course.

Flexible denotes the tendency of all courses in ibis type of structure to conform to the same shape under traffic.

A typical flexible-pavement structure is shown in Figure 5-1, page 5-2. It illustrates the terms used in this manual that refer to the various layers. All the layers shown in Figure 5-1 are not present in every flexible pavement. For example, a flexible-pavement structure may consist only of an asphaltic-concrete surface, a base course, and the subgrade. The design of flexible pavements must include a thorough investigation of the subgrade conditions; borrow areas; and sources of select, subbase, and base materials.

## Tests

Flexible pavements are used almost exclusively in the TO for road and rear area airfield construction. They are adaptable to almost any situation, and they fall within the construction capabilities of the combat heavy engineer battalion and its support units. Rigid suited to TO
pavements are generally not construction requirements (un-
Engineers should classify soils according to Chapter 2 of FM 5-410, and then select representative samples for detailed tests.

Detailed tests determine compaction characteristics, CBR values, and other properties needed for designing the flexible-pavement DISTRIBUTION OF LOADS
structure.

Subbase-and base-course materials are tested for compliance with specification requirements for gradation, liquid limit (LL), plasticity index (PI). and CBR values.

When tests arc completed, limiting conditions in the subgrade and subsoil must be determined. Materials are selected for each layer based on their characteristics (gradation, LL, PI. and CBR values).

Flexible-pavement design is based on the principle that the magnitude of stress induced by a wheel load decreases with depth below the surface. Consequently, the stresses induced on a given subgrade material can be decreased by increasing the thickness of the overlying layers (subbase, base, and surface courses). Figure 5-2 shows the distribution of a single-wheel load on two

## 5-2 Subgrades And Base Courses

The distribution of pressures under a multiple-wheel assembly is shown in Figure 5-3, page 5-4. Multiple-wheel assemblies are beneficial because the stress distributions produced by the tires do not overlap to a large degree at shallow depths. This is illustrated at line A-A in Figure 5-3. Therefore, multiple-wheel assemblies are beneficial on thin, flexible- pavement structures constructed on subgrades with high-bearing capacity. The intensity of stress at a given point in a flexible pavement is affected by the tire-contact area and tire pressure. The major difference in stress intensities caused by variation in tire pressure occurs near the surface. Consequently, the surface course
(pavement or a well-graded crushed aggregate) and base course arc the most seriously affected by high tire pressures.

sections of flexible pavement. one with a thick and one with a thin flexible-pavement structure. In both cases, the subgrade is the found ation that eventually carries any load applied at the surface. Figure 5-2
demonstrates that the magnitude of the stresses on the subgrade decreases as the flexible-pavement structure is thickened. In the left diagram in Figure 5-2, the flexiblepavement structure is thick, the load at the subgrade level is spread over a wide area, and the stresses on the subgrade arc low.

In the right diagram the structure is thin, the load at the subgrade level is confined to a much smaller area, and the stresses on the subgrade level are significantly higher.

The pattern of decreasing stresses with increasing depth is the basis of the conventional flexible-pavement design in which subgrade materials of low-bearing capacity arc covered with thick flexible-pavement structures.

## Subgrades Grade Line

Using information from a deliberate soil survey as outlined in Chapter 2 of FM 5-530, consider the following factors when determining the suitability of a subgrade:

- General characteristics of the subgrade
soils.
- Depth to bedrock. - Depth to the water table. - Compaction that can be attained in the
subgrade.
Classify the subgrade soil in accordance with the Unified Soil Classification System
(USCS) (as described in FM 5-410) and consider the previously listed factors to determine the suitability of a subgrade material. When locating the grade line of a road or airfield, consider the suitability of the subgrade, the depth to the water table, and the depth to bedrock.

Generally, the grade line should be established to obtain the best possible subgrade material consistent with the design parameters. However, simplicity of construction must also be considered.

- CBR values of uncompacted and compacted subgrades.

## Compaction

- Presence of weak or soft layers or organics in the subsoil.
- Susceptibility to detrimental frost action
or excessive swell.
Compaction normally increases the strength of subgrade soils, The normal procedure is to specify compaction according to the requirements in Figure 5-4. A specification block should be used to determine limits for density and moisture content.

Compaction is relatively simple in fill sec-
Specific requirements for minimum depth of tions because all the layers are subjected to subgrade compaction for both cohesive and construction processes and can be comcohesionless soils for road designs are depacted during construction. Compaction is scribed in Chapter 9 of this FM. This same more difficult in cut sections. Compaction information for airfield designs is described must be obtained during construction to a in Chapter 12 of FM 5-430-00-2/AFPAM 32-
depth at which the natural density of the
8013, Vol 2.

material will resist further consolidation under traffic.

## Subgrade CompactionNormal Cases

paragraphs describe the soils in which these conditions may occur and suggested methods of treatment.

## Soils That Lose Strength

The types of soils that decrease in strength when remolded are generally in the USCS
CH, MH, and OH groups. They are soils that have been consolidated to a very high degree, either under an overburdened load by alternate cycles of wetting and drying or by other means, and they have developed a definite structure. They have attained a high strength in the undisturbed state.

Scarifying, reworking, and rolling these soils in cut areas may reduce the soil's loadbearing capacity.

Cohesionless soils (except silts) can be compacted from the surface with heavy rollers or very heavy vibratory compactors. Cohesive soils [including silts) cannot be compacted in thick layers. In cut areas consisting of cohesive soils, it may be necessary to remove the subgrade material and replace it with sequential lifts capable of being compacted to the required density. As a rule of thumb, initially replace material in 6-inch lifts, then adjust the lift thickness up or down, as necessary, to determine the minimum compactive effort. Compaction of cohesive soil is best achieved with penetrating rollers such as tamping or sheepsfoot. Compare the subsoil with compaction requirements for the subgrade (as described in Chapter 9 of this FM and Chapter 12 of FM 5-430-00-2/AFPAM 32-8013, Vol 2) to determine if consolidation of the subsoil is likely to occur under the design traffic load.

If such consolidation is likely to occur, provide a means for compacting the subsoil or design a thicker flexible-pavement structure to prevent subsoil consolidation.

When these soils are encountered, obtain CBR values for the soil in both the undisturbed and disturbed conditions. Compact the soil that is removed to the design density at the design moisture content. Other samples should be compacted to the design density across the range of specified moisture contents. If the undisturbed value is higher than the laboratory test results, no compaction should be attempted and construction operations should be conducted to produce the least possible soil disturbance.

Since compaction should be avoided in these cases, the total thickness design above the subgrade may be governed by the required depth of compaction rather than the CBR method. (See Chapter 3 of TM 5-
825-2.)

## Silts

Cohesive materials, including those of relatively low plasticity showing little swell, should be compacted at the optimum moisture content determined from the densitymoisture curves developed for that soil using the 55-blows-per-layer compactive effort
(CE 55) test. CE 55 may also be designated for ASTM 1557, the American Society of Testing and Materials code for densitymoisture curves. Cohesionless, free-draining materials should be compacted at moisture contents approaching saturation.

## Subgrade CompactionSpecial Cases

Although compaction normally increases the strength of soils, some soils lose stability when scarified and rolled. Some soils shrink excessively during dry periods and expand excessively when they absorb moisture. Special treatment is required when these soils are encountered. The following The bearing capacity of silts, very fine sands, and rock flour (predominantly USCS
ML and SC groups) is reasonably good if properly compacted within the specified moisture range. Compaction of deposits of silt, very fine sand, and rock flour located in areas with a high water table can pump water to the surface. The material becomes quick or spongy and practically loses all load-bearing capacity. This condition can also develop when silts and poorly draining, very fine sands are compacted at a high moisture content. Compaction reduces the air voids so that the available water fills the void space.

Therefore, it is difficult to obtain the desired compaction in these silts and very fine sands at moisture contents greater than optimum.

son and the soils absorb moisture during a subsequent wet season. If the moisture content of the compacted soil increases after compaction, the soil will swell and produce large, uplift pressures. This action may result in unacceptable differential heaving of flexible pavements.

For military construction, swelling soils are placed at moisture contents that will not result in more than a 3-percent change in volume if soil moisture is later increased.

Water from a wet, spongy silt subgrade often enters the subbase and base during compaction through capillary action. This additional moisture may have detrimental effects on bearing capacity and frost susceptibility. If the source of water can be removed, it is usually not difficult to dry these deposits.

These soils usually crumble easily and scarify readily. If the soils can be dried, normal compaction effort should be applied. However, removing the source of the water is often very difficult and, in some cases, impossible in the allotted construction period.

Preswelling is a common method for treating subgrade soils with expansive characteristics. The soil should be compacted at a moisture content at which a 3-percent or greater swelling has already occurred. This reduces the impact of future expansion. Proper control of moisture content is the most important item to remember for swelling soils.

## Selection Of Subgrade And Subsoil Design Cbr Values

In areas with a high water table, drying is not possible until the water table is sufficiently lowered.

Compaction operations will continue to cause water to be pumped to the surface. Areas of this nature are best treated by replacing the soil with subbase and base materials or with a dry soil that is not adversely affected by water.

The CBR test described in FM 5-530 includes procedures for conducting tests on samples compacted in test molds (design density and soaked for four days) and for taking in-place CBR tests on undisturbed samples.

These tests are used to estimate the CBR that will develop in the prototype structure.

Where the design CBR is above
20, the subgrade must also meet the gradation and Atterberg limit requirements for a subbase given in Table 5-1.

Do not disturb the subgrade where drainage is not feasible or a high water table cannot be lowered. Also, do not disturb the subgrade in cases where soils become saturated from sources other than high water tables and cannot be dried (as in construction during wet seasons). Compaction of lifts during wet periods can cause fines from the subgrade to contaminate upper layers of the flexible-pavement structure.

## Subgrade Stabilization

The pumping and detrimental actions previously described should be anticipated whenever silts or very-fine-sand subgrades are located in areas with a high water table. Pumping action limits the ability to obtain the desired compaction in the immediate overlying material.

## Swelling Soils

Subgrades can be stabilized mechanically
(by adding granular materials), chemically
(by adding chemical admixtures), or with a stabilization expedient (sand-grid, matting, or geosythetics).

Stabilization with chemical admixtures (lime, port-land cement, fly ash, and such) is generally costly but may prove to be economically feasible, depending on the availability of the chemical stabilization agent in comparison with the availability of granular material. Chemically stabilized layers should be designed according to the criteria presented in Chapter 9 of FM
5-410.

Soils are characterized as swelling if they display a significant increase in volume with the addition of moisture. These soils can cause trouble in any region where construction is accomplished during a dry seaavailability of these materials must be weighed with the considerable time savings for use of expedients in combat construction.

If mechanical stabilization is used and the stabilized material meets the gradation and Atterberg limit requirements in Table 5-1, it can be assigned a subbase CBR rating. If it does not meet the requirements for a subbase, the material must be considered a select material.

## Frost Susceptibility Of Subgrade

A stabilization expedient may provide significant time and cost savings as a substitute to other means of stabilization or low strength fill. The most popular of the manmade stabilizers are sand grid, roll-matting, and various types of geosynthetics, especially geotextiles. Matting and sand grid are expedient methods of stabilizing cohesionless soils such as sand for unsurfaced road construction. Geotextiles and other geosynthetics are primarily used to reinforce weak subgrades, maintain the separation of soil layers, and control drainage through the road or airfield design. The In areas subjected to seasonal freezing and thawing, subgrade materials may exhibit frost heave and thaw weakening. Table
5-2 lists the frost-susceptibility ratings of soils. Those materials with the F3 and F4
classifications are extremely frost-susceptible, especially if the water table is less than
5 feet below the top of the subgrade. Silty soils are particularly susceptible and their CBR value may be less than 1 during thawing periods. The thaw period and resulting degraded soil strength may last from one to four weeks. Emphasis must be placed on reducing traffic loads during this period to help reduce the possibility of damage.

## Select Materials And Subbase Courses

When designing flexible pavements, locally equal to 20 are called select materials, and available or other inexpensive materials may those with CBR values greater than 20 are be used between the subgrade and base called subbases.

course.

These layers are designated in this manual as select materials or subbases.

Where the CBR value of the subgrade, with-
Those with design CBR values less than or out processing, is in the range of 20 to 50,

## 5-8 Subgrades And Base Courses

select materials and subbases may not be and CL groups may be used in certain needed. However, the subgrade cannot be assigned a design CBR value greater than
20 unless it meets the gradation and plasticity requirements for subbases.

cases. Consider lime rock, coral, shell, ashes, cinders, caliche, and disintegrated granite when evaluating sources of select material. To qualify as a select material, a material must meet the gradation and Atterberg limit requirements established in Table 5-1. A maximum aggregate size of 3
inches will aid in meeting aggregate gradations.

## Subbase Materials

Where subgrade materials meet plasticity requirements but are deficient in grading requirements, it may be possible to treat an existing subgrade by blending in stone, lime rock, sand, or similar materials to produce an acceptable subbase and raise the design CBR value.

## Materials Select Materials

Select materials will normally be locally available, coarse-grained soils (classified G
or S), although fine-grained soils in the ML
Subbase materials may consist of naturally occurring, coarse-grained soils or blended and processed soils. Lime rock, coral, shell, ashes, cinders, caliche, and disintegrated granite may be used as subbases when they meet the requirements in Table
5-1, page 5-8. The existing subgrade may meet the requirements for a subbase course, or it may be possible to treat the existing subgrade to produce a subbase. Do not admix native or processed materials unless the unmixed subgrade meets the LL
and PI requirements for subbases.

material with a measured CBR value of 37, which meets the gradation and Atterberg limit requirements for a CBR 40 subbase, should be used as a CBR 37 subbase. Conversely, if the material failed to meet the CBR 40 subbase requirements (gradation and Atterberg limits) but met the CBR 30
subbase requirements, it would be used as a CBR 30 subbase rather than a CBR 37.

A suitable subbase may be formed using material stabilized with commercial admixtures.

Portland cement. hydrated lime, fly ash, and bituminous materials are commonly used for this purpose. The plasticity of some materials can be decreased by adding lime or portland cement, enabling them to be used as subbases.

## Compaction

Some natural materials develop satisfactory CBR values but do not meet the gradation requirements in Table 5-1. These materials may be used as select or subbase materials, as appropriate, if supported by adequate inplace CBR tests on construction projects using the materials that have been in service for several years.

Select and subbase materials can be processed and compacted using normal compaction procedures.

Specify compaction according to the criteria described in Figure 5-4, page 5-5.

## Selection Of Design Cbr

The CBR test is not applicable for use in evaluating materials stabilized with chemical admixtures.

These chemically stabilized soils must be assigned an equipment CBR value based on the type of admixture and method of application. (See Chapter 9 of FM 5-410.) Ratings as high as 100 can be assigned to these materials when proper construction procedures are followed.

## Potential For Frost Action

Select and subbase materials which are subjected to freezing and thawing may exhibit detrimental frost effects. Although these materials generally are not affected by excessive frost heave, they may lose up to 50 percent of their strength during thawing conditions. This is especially true of materials which have more than 20 percent fines (particles passing the Number (No.) 200 sieve).

If possible, materials listed in Table 5-2, page 5-9, as NFS, S1, S2, F1, or F2 should be used as subbase and select materials in seasonal frost and permafrost areas.

CBR tests are usually conducted on remolded samples.

However, where existing similar construction is available, conduct CBR tests on material in place when it has attained its maximum expected water content or on undisturbed, soaked samples.

The procedures for selecting test values described in the section on subgrades also applies to select and subbase materials. In order to be used as a select or subbase, the material must comply with the requirements indicated in Table 5-1, including CBR value, gradation, and Atterberg limits.

If a material meets the requirements for gradation and Atterberg limits for the next higher design CBR category, but the material's CBR value does not meet the maximum design CBR for that category, assign the material design a CBR value equal to the measured CBR results. For example, a

## Base Course

The purpose of a base course is to distribshows the distribution of stress through ute the induced stresses from the wheel two base courses.

When the subgrade load so that it will not exceed the strength strength is low, the stress must be reduced of the underlying soil layers. Figure 5-5
to a low value and a thick base is needed.

## 5-10 Subgrades And Base Courses

ence to gradation requirements is not feasible, a safe rule of thumb is to avoid using materials which have more than 15 percent fines (particles passing the No. 200 sieve).

When the subgrade strength is higher, a thinner base course will provide adequate stress distribution. Because the stresses in the base course are always higher than in the subgrade (Figure 5-5), the base course must have higher strength.

## Plasticity Index And Liquid Limit

In addition to the gradation requirement, a base-course material must meet the same PI
and LL requirements for a subbase material as indicated in Table 5-1, page 5-8. Material with a LL greater than 25 or a PI
greater than 5 should not be used as a base course.

The base course is normally the highestquality structural material used in a flexiblepavement structure, having CBR values near the CBR standard material (crushed limestone). Base courses are always cohesionless materials and are normally processed to obtain the proper gradation.

## Compaction Requirements

Give careful attention to the selection of materials for base courses. The materials should be dense and uniformly graded so that no differential settlement occurs. For continuous stability, base courses must meet gradation and plasticity requirements.

Base-course material must be capable of being compacted to meet the requirements given in Figure 5-4, page 5-5. When constructing a base course, lift thickness must be based on the ability to attain the required density.

Lift thickness is dependent on the type of material, the compaction equipment used, and the method of construction.

## Gradation

Normally, a material used as a base course must meet the gradation requirements outlined in Tables 5-3, 5-4 and 5-5, page 5-12 (depending on the type of material). Determine gradation ing mechanical of the proposed material usanalysis.

If strict adher-
The CBR of the finished base course must conform to that used in the design. The total compacted thickness must equal that obtained from the flexible-pavement design curves, Table 5-6, page 5-13 lists nine types of materials commonly used as base

## 5-12 Subgrades And Base Courses

by blending materials from two or more deposits. Uncrushed, clean, washed gravel is normally not suitable for a base course because not enough fines are present.

Fines act as a binder and fill the voids between coarser particles.

Sand and Clay.

Natural mixtures of sand and clay are often located in alluvial deposits of varying thicknesses. Often there are great variations in the proportions of sand and clay from the top to the bottom of the deposit. Depending on the proportions of sand and clay, these deposits may also provide suitable base-course materials. With proper proportioning and construction methods, satisfactory results can be obtained with sand-clay soils.

courses for roads and airfields.

A typical design CBR is given for each type of material.

Laboratory CBR tests to determine design CBR are not necessary.

Deposits of partly disintegrated rock that consist of fragments of rock, clay, and mica flakes should not be confused with sandclay soils.

The mica flakes make the deposit unsuitable for use as a base course.

Mistaking these deposits for a sand-clay soil may result in base-course failure.

## Processed Materials Materials

Natural, processed, and other materials are used for base courses. Descriptions of these materials follow.

## Natural Materials

Processed materials are made by crushing and screening rock, gravel, or slag. A
properly graded, crushed rock base-course material produced from sound, durable rock makes the highest-quality base material.

Existing quarries; ledge rock; cobbles and gravel: talus deposits; coarse mine tailings; and similar hard, durable rock fragments are the sources of processed materials.

Table 5-3 shows the common rock types that are generally suitable for base-course material. Generally, rock which is hard enough to require blasting during excavation makes suitable base-course material.

A wide variety of gravels; sands: gravelly and sandy soils; and other natural materials such as lime rock, coral, shells, and some caliches can be used alone or blended as a suitable base course. Sometimes natural materials require crushing or removal of oversize material to maintain gradation limits.

Some natural materials may be suitable for use as a base course by mixing or blending them with other materials.

Base courses made from processed materials can be divided into three general types: stabilized, coarse-graded, and macadam.

can Sand and Gravel. Many natural deposits of sandy and gravelly materials make satisfactory base-course materials, Gravel deposits differ widely in the relative proportions of coarse- and fine-grained material and in the character of the rock fragments. Satisfactory base materials can often be produced Stabilized. In a stabilized base course, material ranging from coarse to fine is mixed to meet the gradation requirement given in Table 5-4.

The mixing process be accomplished in advance (at a cementing action that results in a satisfactory base.

processing plant) or during the placing operation. Because the aggregates produced in crushing operations or obtained from deposits are often deficient in fines, it may be necessary to blend in selected fines to get a suitable gradation.

Screenings, crusher-run fines, or natural clav-free soil may be added for this purpose. Coarse-Graded. A coarse-graded type of base course is composed of crushed rock, gravel, or slag, When gravel is used.

50 percent of the material by weight must have two or more freshly fractured faces, with the area of each face equal to at least
75 percent of the smallest midsectional area of the piece.

These materials cannot be judged on the basis of the gradation limits used for other materials. Rather, they arc judged on the basis of service behavior. Strength tests on laboratory samples arc not satisfactory because the method of preparing the sample seldom replicates the characteristics of the material in place. The PI is a reasonably good criterion for determining the suitability of these materials as base courses.

As a general rule, a low PI    is a necessity.

However, observation of these types of base materials in existing roads and pavements is the most reliable indicator of whether or not they will be satisfactory.

Macadam. The term *macadam* is usually applied to construction in which a coarse, crushed aggregate is placed in a relatively thin layer and rolled into place. Fine aggregate or screenings are placed on the surface of the coarse-aggregate layer and rolled and broomed into the coarse rock until it is thoroughly keyed in place. Water may be Used in the compacting and keying process.

When water is used, the base is termed a water-bound macadam. The crushed rock used for macadam base courses should consist of clean, angular, durable particles free of clay, organic matter. and other unwanted material or coating, Any hard, durable, crushed aggregate can be used, provided the coarse aggregate is one size and the fine aggregate will key into the coarse aggregate.

Aggregates for macadam-type con -
struction should meet the gradation requirements given in Table 5-5, page 5-12.

Coral.

Coral is commonly found along the coastlines of the Pacific Ocean and the Caribbean Sea. Coral is normally very angular and, as such, its greatest assets as a construction material are its bonding properties. These properties vary, based on the amount of volcanic impurities, the proportion of fine and coarse material, and the age and length of exposure to the elements.

Proper moisture control, drainage, and compaction arc essential to obtain satisfactory results. Avoid variations of more than 1
percent from optimum moisture content. Uncompacted and poorly drained coral is susceptible to high capillary rise, resulting in too much moisture and loss of stability.

Sprinkling with sea water or sodium chloride in solution promotes bonding when rollers are used. As a rule of thumb, coral should cure for a minimum of 72 hours after compaction is completed.

## Other Materials

Caliche. Caliche is a by-product of chemical weathering processes. It is composed of limestones, silts, and clays cemented together by lime, iron oxide, or salt.

Caliche has been used extensively in arid regions as a base material because of its ability to recement when saturated with water, compacted, and given a setting period. Caliche varies in content (limestone, silt, and clay) and in degree of cemen -
tation. It is important that caliche of good, uniform quality be obtained from deposits In some TO areas, deposits of natural sand and gravel and sources of crushed rock are not available. This has led to the development of base courses from materials that normally would not be considered. These include caliche, lime rock, shells, cinders, coral, iron ore, rubble, and other similar materials. Some of these materials arc weak rock that crush or degrade under construction traffice to produce composite base materials similar to those described in the preceding paragraphs. Others develop a

## 5-14 Subgrades And Base Courses

and that it be compacted within a specified moisture range.

thick. If a bituminous base is used, the binder and leveling courses may be omitted and the surface course may be laid directly on the base course.

## Selection Of Base Course

After caliches have been air-dried for 72
hours, the LL of the material passing the No. 40 sieve should not exceed 35, and the PI should not exceed 10. For base-course material, caliches should be crushed to meet the following gradations:

Percent passing 2-inch sieve
100
Percent passing No. 40 sieve
15-35
Percent passing No. 200 sieve
0-20

Stripping should be used to remove undesirable material from surface deposits of caliche.

Selection of the type of base-course construction depends on the materials and equipment available and the anticipated weather conditions during construction. A
complete investigation should be made to determine the location and characteristics of all natural materials suitable for basecourse construction. Base courses of untreated natural materials are less affected by adverse weather and normally require less technical control. Untreated bases are relatively easy and fast to build and are preferable to bituminous or cement-stabilized types.

This is true even where suitable admixture materials for such construction are readily available, which is not true in many areas of the world.

Tuff. Tuff and other cement-like materials of volcanic origin may be used for base courses. Tuff bases are constructed in the same manner as other base courses except that the oversize pieces are broken and the base is compacted with sheepsfoot rollers after the tuff is dumped and spread. The surface is then graded and final compaction and finishing are accomplished.

## Special Considerations For Seasonal Frost And Permafrost Conditions

Rubble. The debris or rubble of destroyed buildings may be used in constructing base courses. Jagged pieces of metal and similar objects must be removed: large pieces of rubble should be broken into 3-inch pieces or smaller. Caution should be exercised when using rubble in a tactical environment to avoid mines or booby traps.

Since base-course materials are near the surface of the road or airfield, the amount of strength loss during thawing periods will have a strong influence on the life of the facility. If possible, materials listed in Table 5-2, page 5-9, as nonfrost susceptible
(NFS), or possibly frost susceptible (S1 or S2) should be used as base courses in seasonal frost and permafrost areas.

## Construction Operations

Construction operations for roads and airfields include the following tasks which are organized according to the construction schedule and quality control plan for the project.

## Fine Grading

Bituminous Base. In general, a bituminous base course may be considered equal, on an inch-for-inch basis, to other types of high-quality base courses. Bituminous mixtures are frequently used as base courses beneath high-use bituminous pavements, particularly for rear-area airfields carrying heavy traffic, Bituminous bases may be advantageous when locally available aggregates are relatively weak and of poor quality, when mixing-plant and bituminous materials are readily available, or when a relatively thick structure is required for the traffic.

When a bituminous base course is used, it is placed in lifts no more than 3 1/2 inches The subgrade is fine graded to achieve the desired cross section established by final grade stakes.

Before placing select material, subbase, and base course, the subgrade should be compacted to attain the required density, and ruts and other soft spots should be corrected.

## Hauling, Placing, And Spreading

grader is used, thoroughly mix the materials by blading the windrows of materials from one side of the area to the other, with the blade of the grader set to give a rolling action to the material. The coarse and fine aggregates can also be mixed in mechanical plants (mobile or stationary) or on a paved area with graders and bucket loaders. Proportionally distribute the coarse and fine aggregates by weight or volume in quantities so that the specified gradation, LL, and PI requirements are attained after the base has been placed and compacted. Mixing operations should produce uniform blending.

Placing and spreading material on the prepared subgrade may begin at the point nearest the borrow source or at the point farthest from the source. The advantage of working from the point nearest the source is that the haul vehicles can be routed over the spread material, which compacts the base and avoids damage to the subgrade. An advantage of working from the point farthest from the source is that hauling equipment will further compact the subgrade.

Also, this practice will not overwork the base course, which can cause unwanted segregation. This method also reveals any weak spots in the subgrade so that they can be corrected prior to placement of the base courses, and interferes less with spreading and compaction equipment.

When mechanical mixing is used, place the coarse and fine aggregates in separate stockpiles or adjacent windrows to permit easy proportioning. When bucket loaders are used, place the fine- and coarse-aggregate portions in adjacent windrows on a paved area.

Blade the windrows together to meet the requirements specified for the project.

## Watering Base Materials

The self-propelled aggregate spreader is the preferred piece of equipment for placing a base course.

If a self-propelled spreader is not available, base-course material can be spread using towed spreaders, scrapers, or dump trucks. If equipment capable of spreading the aggregate in even lifts is not available, the material can be initially dumped in long windrows and subsequently spread with graders, dozers, or front-end loaders.

As in subgrade-compaction operations, obtaining the specified compacted density requires that the material be placed and compacted at a moisture content inside the specification block.

The moisture content of the base material at the site can be obtained by a nucIear densometer, a speedy moisture tester, or by expedient methods. Given the on-site moisture content, the engineer in charge can calculate exactly how much water is to be added or if the base needs to be aerated to achieve the specified moisture content range.

Lift thickness should be based on the ability to compact the material to the required density. A good rule of thumb is to initially place the base course in 6-inch lifts. After testing the compacted density, increase or decrease the lift thickness as necessary to meet the project requirements.

## Blending And Mixing

Controlled watering can be done with a truck-mounted waler distributor. Asphalt distributors should not be used because the pump lubrication system is not designed for water.

Any container capable of movement and gravity discharge of water may be used as an expedient water distributor.

## Compacting

Materials to be blended and mixed should be spread on the road, runway, or taxiway in correct proportions, with the finer material on top.

Fold the fine material into the coarser aggregate with the grader blade.

If available, dry-mix the material using blades, disks, harrows, or rototillers, leaving the material in windrows. When a Base-course compacting must produce a uniformly dense layer that conforms to the specification block. Compact base-course material with vibratory or heavy.

## 5-16 Subgrades And Base Courses Preparing Subgrade

If a macadam base course is constructed on a material with high plasticity, there may be base infiltration.

This can be prevented with a blanket course of fine material such as crusher screenings or 3 to 4 inches of sand. The blanket course should be lightly moistened and rolled to a smooth surface before spreading the coarse macadam aggregate. A membrane or a geotextile fabric may be used in lieu of the blanket course.

## Spreading

rubber-tired rollers. Maintain moisture content during the compaction procedure within the specified moisture-content range.

Compact each Iayer through the full depth to the required density. Measure field densities on the total sample. Use a test strip to determine which rollers are most effective and how many roller passes are necessary to achieve the desired compaction.

The care and judgment used when constructing the base course will directly reflect on the quality of the finished flexible pavement. Base-course layers that contain gravel and soil-binder material may be compacted initially with a sheepsfoot roller and rubber -tired rollers. Rubber-tired rollers are particularly effective in compacting base materials if a kneading motion is required to adjust and pack the particles. Base courses of crushed rock, lime rock, and shell are compacted with vibratory, steel-wheeled, or rubber -tired rollers. Select the equipment and methods on each job to suit the characteristics of the base material. When using rollers, begin compaction on the outside edges and work inward, overlapping passes by one-half of a roller width.

## Finishing

Macadam aggregate must be placed and spread carefully to ensure that hauling vehicles do not add objectionable material to the aggregate.

Care is particularly necessary when placing the aggregate at the point nearest to the source and routing hauling vehicles over the spread material. If the compacted thickness of the lift is 4 inches or less, spread the loose macadam aggregate in a uniform layer of sufficient depth to meet requirements. For greater compacted thickness, apply the aggregate successively in two or more layers. Spreading should be from dump boards, towed aggregate spreaders, or moving vehicles that distribute the material in a uniform layer. When more than one layer is required, construction procedures are identical for all layers.

## Compacting

Finishing operations must closely follow compaction to furnish a crowned, light, water-shedding surface free of ruts and depressions that would inhibit runoff. Use the grader for finishing compacted aggregate bases. Blade the material from one side of the runway, taxiway, or road to the middle and back to the edge until the required lines and grades are obtained. Before final rolling, the bladed material must be within the specified moisture-content range so it will consolidate with the underlying material to form a dense, unyielding mass. If this is not done, thin layers of the material will not be bound to the base, and peeling and scabbing may result. Final rolling is done with rubber-tired and steelwheeled rollers.

Immediately following spreading, compact the coarse aggregate the full width of the strip by rolling it with a steel-wheeled roller.

Rolling should progress gradually from the sides to the middle of each strip in a crown section, and from the low side to the high side where there is a transverse slope across the road, runway, or taxiway. Continue rolling until the absence of creep or wave movement of the aggregate ahead of the roller indicates that the aggregate is stable.

Do not attempt rolling when the subgrade is softened by rain.

## Applying Screenings Special Procedure For Macadam Bases

After the coarse aggregate has been thoroughly stabilized and set by rolling, distribute sufficient screenings (fine Construction of macadam base courses requires the procedures that follow.

## Slush Rolling

aggregates) to fill the voids in the surface.

Roll continuously while screenings are being spread, so the jarring effect of the roller will cause them to settle into surface voids.

Spread screenings in thin layers by using hand shovels, mechanical spreaders, or moving trucks.

Do not dump them in piles on the coarse aggregate. If necessary use hand or drag brooms to distribute screenings during rolling.

The purpose of slush rolling (rolling with enough water to produce a slushy surface)
is to achieve compaction when conventional methods fail.

Slush rolling should be permitted only on a free-draining, cured base course. Slushing requires a considerable amount of water on the surface.

The quantity varies greatly with the type of material, the temperature, and the humidity. If the surface is generally satisfactory but has some large areas requiring slushing, slush only the rough areas. Slushing brings fines to the top and creates voids. In general, slush rolling should not be used on a highquality base-course material. It should be used only when required by the specifications or when conventional compaction methods have failed.

## Applying Water

Do not apply screenings 100 thick because they will bridge over the voids and prevent the direct bearing of the roller on the coarse aggregate. Continue spreading, sweeping, and rolling until no more screenings can be forced into the voids. Start sprinkling the surface with water after the screenings have been spread. The sprinkling causes the screenings to be flushed down into the voids of the aggregate. The surface is then rolled. Do not saturate and soften the subgrade.

Continue sprinkling and rolling until a mixture of screenings and water forms, fills all voids, and gathers in a small wave before each roller. When a section of a strip has been grouted thoroughly, allow it to dry completely before performing additional work.

Engineers must calculate a water application rate in terms of gallons per square yard in order to allow the water distributor operator to accurately apply water. A
reasonable estimate for applying water to a
6-inch lift is 0.5 to 1.0 gallon per square yard. The rollers must follow immediately behind the water truck to achieve the desired results because the roller should carry a wave of water ahead of it as it passes over the base course.

## Finished Surfaces Rolling Equipment

Use pneumatic-tired, vibratory, or steelwheeled rollers to obtain a smooth finish on the base course. Continue rolling until compaction has been obtained.

## Finishing

The base-course surface determines the smoothness of the finished pavement. If the finished base dots not conform to the specified grade when tested with a 12-foot straightedge, the finished pavement also will not conform. The base surface should be smooth and conform to specified design requirements.

There are usually small rivulets or ridges of fines left on the surface after slushing is completed.

Where these are excessive or when the thickness of the blanket of fines is excessive, sprinkle the surface with water and hone (dress lightly) with a grader blade. This delicate operation requires a good operator and a sharp, true blade. Follow the grader immediately with a pneumatic roller to reset the surface.

When tested with a 12-foot straightedge applied parallel and perpendicular to the centerline of the paved area, the surface of the base course should not show any deviation in excess of 3/4 inch for roads and airfields
[for propeller-type aircraft) or 1/8 inch for jet aircraft. Correct any deviation in excess of these figures, and remove material to the total depth of the lift, replacing with new material and compacting as specified above.

## Wet Rolling

All base courses require a final surface finish. The final finish should be obtained immediately after final compaction or proof rolling.

For less critical base courses or where deemed necessary by the project engineer, wet rolling and slush rolling may be used to obtain the final finish. Both methods have strong points and, in some cases, a job may require a combination of the two.

ser particles of the base course will be carried along by the blade to form a windrow at the edge of the section being finished.

This coarse aggregate can be evenly distributed over the area and incorporated into the surface of the base by a steel-wheeled roller closely following the grader. Additional water may be required, and rolling by the steel-wheeled and pneumatic-tired rollers must be continued until a smooth, dense surface is obtained. This method can also be used for correcting minor surface irregularities in the base course.

## Applying Water Quality Control

Wet rolling does not require the large amount of water demanded for slush rolling, and the base course does not need to go through the curing period required by the slush-rolling method. Apply enough water to the base course to raise the moisture content of the upper 1 to 2 inches of the base course to approximately 2 percentage points above the minimum moisture content. The percent of moisture will vary with the type of material and is a matter of judgement by the project's quality control manager.

## Finishing

Quality control is essential to any project's success.

Although visual inspection is important, it is not, by itself, sufficient to control the construction of all courses described in this chapter, particularly those which contain considerable fine material.

Depending on the type of base, control tests will include determinations of gradation, mixing proportions, plasticity characteristics, moisture content, field density, lift thickness, and CBR values. These tests are described in detail in FM 5-530. Prior to starting construction, a detailed quality control plan should be developed which addresses testing procedures, frequency, location and, most importantly, remedial actions.

Finish the surface by having the grader blade lightly cut the final surface. The light blading will loosen the fines; the coar-
Design Considerations Ponding Areas Drainage Preliminary Measures Design Procedures Section II. Open-Channel Design Section III. Culverts The Hydrograph Drop Inlets and Gratings Culvert Types and Designs Drainage-System Design Design Factors Section I. Construction Drainage Drainage Hydrology Estimating Runoff Using the Rational Method Design Techniques

Subsurface Drainage
Section IV. Surface Drainage Design in Arctic and Subarctic Regions
Fords, Dips, Causeways, and Bridges
Erosion Control
Nonuse Areas and Open Channels
Culvert Outlets

## Drainage

Inadequate drainage is the most common cause of road and
airfield failure.
               Therefore, drainage is a vital consideration in
planning, designing, and building military roads and airfields.
It is important during both construction and use.

## Section I. Construction Drainage

Commanders and construction supervisors continuously emphasized by the command.

must ensure continuous maintenance of the Construction drainage must be completed drainage system during construction of a before needed; when a storm begins it is military road or airfield. The construction too late to start drainage work. Construcdrainage system is temporarily established tion-drainage measures used during difto prevent construction delays and strucferent phases of construction are discussed tural failure before completion. Generally, below.

long delays will result if drainage is not

## Preliminary Measures Reconnaissance

- Vegetation or cover that, if removed
during the clearing and grubbing phase
of construction, could increase surface
runoff.
Prior to the start of construction, preliminary reconnaissance of an area should disclose features that require advance drainage planning and operations. These features include

- Springs and seepage on hillsides which
may indicate perched or high water
tables detrimental to cuts.
Z The presence of level areas which have
good vegetation and adjacent slopes.
These areas may indicate a shallow
groundwater table with capillary water
movement and may require intercepting
subsurface drainage.
Z Streams that should be checked for normal high-water and flood indicators.

## Protective Measures

Z Trees adjacent to dry or low-flow
streams that could receive their root
water from a groundwater table flowing
near the surface. Compacted fills
across such areas could change the movement of the flow.
Controlling runoff during construction can be costly, The following measures can help the following factors with regard to construction stripping:
maintain satisfactory drainage during construction:

- Make maximum use of existing ditches
and drainage features. Where possible,
grade down hill to allow economical grading and to take advantage of natural
drainage
- Select a disposal area that will not interfere with or divert the drainage pattern
of surface runoff. If the drainage pattern is disturbed, the stripped material
may form a barrier resulting in pending
and may otherwise affect adjacent areas.
Z Be aware that removing the vegetation
from an area can lead to excessive surface runoff and erosion. This could
lead, in turn, to silting of channels and
flooding of low areas.
- Use temporary ditches to help construction drainage.
Ensure efforts are made
to drain pavement subgrade excavations
and base courses to prevent detrimental
saturation. Carefully consider the
drainage of all construction roads, equipment areas, borrow pits, and
waste areas.
- Consider that serious bank erosion due
to surface runoff may occur if vegetation adjacent to the banks of streams or
ditches is removed. To avoid this, it
may be necessary to leave the vegetation or to provide a berm with a chute.
Z Be aware of areas where open excavation can lead to excessive erosion. The
discharge of turbid water to local
streams will require temporary retention structures.
- Hold random excavation to a minimum,
and sod or seed finished surfaces immediately.
Z In large, cleared areas, control runoff
sediments to prevent failure of other structures and possible adverse environmental effects. This is more of a contern in permanent construction than in
wartime TO construction.

## Clearing, Grubbing, And Stripping

Z Plan timely installation of final stormdrain facilities and backfilling operations to allow maximum use during construction.

## Area Clearing

The following constraints should be considered:

## Existing Drainage

Any clearing, grubbing, and stripping must include filling holes and back dragging or grading to a slight slope. This will ensure proper runoff and prevent water from collecting and saturating the subgrade. If filling and grading is not done, the advent of rain will make it necessary to strip off any wet soil until dry soil is reached to start the fill. Some ditching may be required to direct the surface flow to an outlet point.

## Fill

When placing fill, exercise firm control over the project to prevent adverse effects from improper drainage procedures. Some of the factors requiring attention are
Clear excess vegetation from streams. This increases the velocity and quantity of flow. Widening the stream can also increase the flow. Bends and meanders can be cut to straighten the stream. Use care in making major alignment changes because they can change the hydraulic characteristics of the stream. This change could adversely affect other parts of the stream.

## Vegetation Removal

- The fill section must be rolled smooth at
the end of each working day to seal the surface. No areas should be left that
can hold standing water.
Military projects may require the removal of all vegetation from large areas. Consider consider removing the ditches by backfilling and compacting.

- The fill surface must be kept free of ruts
caused by trucks and other equipment. These depressions collect rain and
saturate the subgrade. Also, the surface must be crowned to discharge
runoff quickly.
Locate interceptor ditches on hillsides and at the foot of slopes to intercept and divert runoff from the construction site. Make these ditches part of the final drainage system wherever possible. Roadside ditches, required during all construction stages, should be placed at design locations.

- When the fill area is large, it may be
necessary to create swales (depressed
areas) to conduct surface runoff to discharge outlets.
During construction, use deep ditches for subsurface drainage. They intercept groundwater flow, as shown in Figure 6-1.

If groundwater flow must be intercepted but ditching is not possible, modify the ditch into a subsurface drainpipe system.

- To allow fill to proceed, it may be necessary to install temporary culverts in the
fill area in places other than final
design locations.
After the fill area has
reached design depth, the design culverts can be properly trenched in place.

## Ditching

Ditching may be required in swamp areas to either continue drainage ditches to an outlet point or drain the area.

Engineers may use explosives in such cases, since the soil may not be capable of supporting construction equipment. Draglines should also be considered.

Use interception ditches during construction to collect and divert surface runoff before building the designed system. Prior to construction, conduct a site investigation of the general layout, consistent with the work plan. When interception ditches cannot be made part of the design drainage.

Timber or steel mats can be used to provide a firm foundation and support equipment during the operation.

## Culverts

Culverts are required during construction to allow surface runoff. If streams must be diverted to allow the construction of permanent culverts, use temporary culverts in the construction area. Never close natural drainage channels, even if they are currently dry.

If these channels are closed, surface runoff from sudden storms could cause a serious problem. These conditions must be anticipated. Construction drainage must keep pace with the construction project.

## Drainage Hydrology

water absorbed depends on the soil type, the vegetation, the terrain slope, and the soil moistness prior to the rain. Stormwater runoff begins to accumulate only when the rate of rainfall exceeds the rate of infiltration.

The hydrologic cycle is the continuous process which carries water from the ocean to the atmosphere, to the land, and back to the sea. A number of different subcycles can take place concurrently in the overall cycle and are discussed below.

## Precipitation Detention

Before overland water flow can begin its downhill motion, it must be deep enough to overcome any obstacles to its movement.

Detention is the amount of water required to fill depressions of any size in the earth's surface.

Except by infiltration or evaporation, no water can leave a depression until the holding capacity of the depression has been exceeded.

## Transpiration

Rainfall is the moisture-delivery mechanism of primary concern to most military drainage designers.

Snowmelt may be of greater concern in colder climates or in the design of reservoirs in milder regions.

These concerns are beyond the scope of this manual, but they are included in TM 5-852-7.

The amount of rainfall that evaporates depends on the surface temperature of ground features, the air temperature, the wind speed, and the relative humidity. Evaporation occurs while rain is falling to the ground and after it lands on vegetation and other ground cover.

## Interception

On a long-term basis, vegetation returns water to the atmosphere through a process called transpiration.

Because of the time involved, transpiration has no immediate effect on water runoff in an area.

## Runoff

Rainfall coming to rest on vegetation is said to have been intercepted. Large quantities of water can be trapped in the leaf canopy of trees and plants.

Rain does not reach the soil until the holding capacity of the vegetation canopy is exceeded.

Evaporation, interception, infiltration, detention, and transpiration are all moisture losses, Runoff is precipitation minus these moisture losses.

## Infiltration Storms

Storms can deliver a large quantity of water to the earth in a short period of time. For A significant portion of the water that actually strikes the soil soaks into the ground. This process is call infiltration.

The rate of absorption and the quantity of

## 6-4 Drainage

that reason, the study of storms is an important part of the study of drainage hydrology.

This section discusses storms in terms of duration, frequency, and intensity.

It describes procedures for determining maximum storms and introduces the subject of runoff.

## Duration

Duration is the length of time a storm lasts, After many years of observation, hydrologists have determined that a storm of long duration usually has low intensity.

In contrast. a high-intensity storm usually has a short duration.

Figure 6-2 shows typical storm hydrography developed by the National Weather Service. Time, usually measured in hours, is depicted horizontally.

The amount of rain for each unit of time is measured vertically in inches. The total amount of precipitation is the area of the graph. The five main types of storms are described below.

## Thunderstorms

Thunderstorms, represented by Figure
6-2(a), are local atmospheric disturbances of short duration and high average rate of rainfall (intensity). They are characterized by thunder, lightning, torrential rain, and sometimes hail, Thunderstorms tend to govern the design of drainage for small areas.

## Moderate Storms

Moderate storms, represented by Figure 6-2(b), cover larger areas for several hours with moderate intensity. These storms period is the probability of having a storm of that value or greater in any one year.

develop greater total precipitation than thunderstorms. The moderate storm normally controls the design of drainage structures for medium-sized basins.

## Long-Duration Storms

For the two-year -frequency storm, the probability of having a storm equalling or exceeding the value in any one year is 0.5
(two out of four times).

The design-storm frequency for TO construction is normally two years. If construction with a longer estimated life is desired, the appropriate design storm should be specified in the authorizing directive.

Long-duration storms, represented by Figure 6-2(c), page 6-5, often have several peaks of high rainfall. Durations may be up to several days, developing very large amounts of precipitation at relatively low average rates of rain fall. With a low average rate of rainfall, such storms have little or no impact on small- or mediumsized drainage basins, but they normally control the design of drainage structures for large basins.

## Monsoons

As with any statistical method of describing essentially random, natural events such as weather, there is a degree of uncertainty.

The two-year design storm occurs on the average every two years; it is not guaranteed to occur every two years. Statistically, the probability of a storm equal to or greater than the two-year design storm occurring in any two years is 0.75 (three out of four times).

Details of the statistics involved can be found in hydrology textbooks.

Monsoons arc seasonal winds of the Indian Ocean and southern Asia. These winds blow from the south during April to October and from the north during the rest of the year. Heavy rains usually characterize the April-to-October season. This rain is not normally continuous; it rises to a peak and then subsides in a cyclic fashion.

## Weather Data Tropical Cyclones

Hurricanes and typhoons are storms caused by severe cyclonic disturbances over a wide area. Precipitation is normally heavy and long.

If there are extensive rainfall and rain-rate records for the location of interest, and if hydrologists have examined those records statistically to formulate intensity-duration tables, then those tables can be obtained through the Air Force staff weather officer.

The staff weather officer is normally located at division level.

## Design Life Versus Actual Life Of A Structure

The design storm is an idealized storm that is expected 10 be equalled or exceeded at least once during the design life of a drainage system.

For example, if a drainage system has been designed for an estimated life of five years, then the design storm will have a five-year frequency. The frequency of a design storm is the average return period of a storm. For example, if a two-year frequency storm has an intensity of 1.5 inches of rainfall per hour, it can be expected that a storm of that intensity or greater will recur an average of once every two years. Two years is also called the return period. The reciprocal of the return Within the United States, the data will generally come from the National Weather Service, either directly or through the Air Force. Overseas, the staff weather officer may be able to obtain data from local government sources, but it may take considerable time to obtain. However, it is unlikely that such pinpoint data is available in many overseas TO locations. When weather data is not available, use rainfall isohyetal maps. Isohyetal maps have contours of equal rainfall intensity just as topographic maps have contours of equal elevation. Figure 6-3 is an isohyetal map of the world, in this case showing the iso-intensity lines for a 60-minute, 2-year storm.

## 6-6 Drainage

To properly read a value on the isohyetal map, find the project location and read the value of the appropriate isohyet(s).

Do not interpolate. If a project location falls

Z On an isohyetal line, read the value of
that isohyet.
To use Figure 6-4, enter the graph using the Duration in Minutes (Tc). Follow the line vertically until it intersects the curve whose number corresponds to the 60-
minute intensity determined from the isohyetal map (or from pinpoint data, if YOU
choose not to draw your own intensity-duration curve). Read horizontally to the left to determine the rainfall intensity (I) in inches per hour. The following is an example:

- Between two isohyets, read the larger
value.

| 2-yr      | Critical   |
|-----------|------------|
| Intensity |            |
| Duration  |            |
|           |            |
| (in/hr)   | (min)      |

- Within an encircling isohyetal line, read
the value of the encircling isohyet.

1.0
5 0
1.2

Examples (in inches per hour (in/hr)):

1.5
3 0
2.4
2.0
10
5.2

## Runoff

| Southern Australia         |   1.0 |
|----------------------------|-------|
| North Dakota               |   1.5 |
| Florida                    |       |
| 2.5                        |       |
| Washington, DC             |   1.5 |
| Vietnam                    |   2.5 |
| Cuba                       |   2.5 |
| New Orleans, Louisiana 2.5 |       |

Note that the intensities just found are for a 60-minute storm. This must now be adjusted to the critical duration of the project under construction. Once the critical duration has been determined, make the adjust -
ment using the standard rainfall intensityduration curves in Figure 6-4.

Precipitation supplies water to the surface, but evaporation, interception, and infiltration begin to draw water at the start of the storm.

Eventually, if the storm is strong enough, vegetation and other surface characteristics, such as depressions and soil, will become saturated, allowing water to flow freely over the surface. This condition is called runoff and is usually measured in cubic feet per second (cfs). Runoff begins sometime after the beginning of precipitation and may continue long after precipitation ends.

The total quantity of runoff from a given area, after it is collected in channels and streams, is the flow estimate used to design an area's drainage structures.

The standard curves are numbered 1.0, 2.0,
3.0, and 4.0, with intermediate values readily interpolated.

Note that curve number 1
passes through 1 inch per hour at 60
minutes, curve number 2 passes through 2 inches per hour at 60 minutes, and so on.

Where intensity is known for any nonarctic location (taken from the isohyetal map, Figure 6-3, page 6-7) and critical duration is calculated, the intensity (1) can easily be determined. (The standard intensity-duration curves are applicable to any frequency, not just a 2-year frequency.)
Transpiration and evaporation also draw from the water supplied by precipitation.

However, these are relatively small losses and will not usually affect military drainage design. Estimating runoff will be discussed later in this chapter. Once the runoff has been determined, necessary ditches and culverts can be designed.

## The Hydrograph

the stream and its tributaries from their banks and the flow from permanent springs and swamps. Depending on the area, climate, and groundwater level, it may flow at a fairly constant rate. Conversely, the flow may fluctuate widely or even cease completely for some periods of time.

Stream-water flow may originate from surface runoff, groundwater, or both. Runoff reaches the stream as overland flow.

Groundwater flow results from side-bank seepage and springs. The hydrography depicts the fluctuations of flow with regard to time.

## Lag Times

The elements of a hydrograph are base flow, lag time, peak flow, lime of concentration (TOC), and flow volume. Each stream will have its own characteristic hydrography with widely varying values for the elements.

A typical stream-flow hydrography is shown in Figure 6-5, page 6-10.

## Base Flow

When precipitation begins over an area, there is an initial period during which the loss factors induced by interception, infiltration, and detention take effect before any surface runoff takes place. Stream flow will increase only when these initial losses have been satisfied and surface runoff begins.

This is known as initial lag time. The length of this lag time is influenced by The base flow of a stream depends upon the amount of groundwater that seeps into

is critical to the drainage engineer, since it
determines the duration of the storm that
will demand the most from the drainage sys-
tem; that is, the storm's critical duration.

## Volume Of Flow

vegetation and other terrain characteristics.

the hydrography peaks at that point. TOC
For example, a grass-covered parking area will have a longer initial lag period than an asphalt parking lot of the same size. A second lag time occurs between the time the stern] reaches its peak pecipitation rate and the time the stream reaches its maximum flow. The length of this secondary lag time is influenced by the size of the area drained. In small- and moderately -
sized drainage areas, there will be only slight differences between storm peak and stream peak.

The area under the curve of the hydrography indicates the total flow, in cubic feet, resulting from any particular storm. It is used in drainage design for determining pending times when it is practical to use culverts with submerged inlets.

## Peak Flow Constructing A Hydrography

A hydrograph is constructed by measuring a stream's rise and fall and the times related to these changes in flow. When constructing a hydrograph
The peak of the hydrography is the maximum stream flow that will occur during a particular storm. In general, peak flow is generated when the entire drained area is discharging its runoff. Peak flow is read directly from the maximum ordinate of the hydrograph This flow determines the size of the drainage structures required at the basin outlet.

- The base flow must be measured at a
time when there have been no recent storms. A field reconnaissance must be made for this measurement.

## Time Of Concentration

- The peak flow can be estimated using
the hasty runoff estimation presented in this chapter.
The TOC is the time it lakes for an entire drainage basin to begin contributing runoff to the stream. Assuming uniform rainfall,

- The general shape of the curve of the
hydrograph will be similar to that
shown in Figure 6-5.

## 6-10 Drainage Drainage-System Design

it away from the work

## Design Data Requirements

area or to divert site.

## Meteorological Data

Before designing a drainage system, survey the various types and sources of drainagerelated information, The survey should include, as a minimum, information concerning the area's topography, meteorological records, soil characteristics, and available construction resources.

Gather information on general climatic conditions, seasonal variations in rainstorms, and intensity and duration of representative storms.

This data can then be applied to the location of the proposed facility.

## Topographical Information Soil Characteristics

Give special attention to the vicinity of the proposed facility as well as the presence of any topographical features that may contribute runoff to the project area. The completed facility often will interfere with the site's natural drainage. Therefore, when analyzing the effects of the surrounding terrain

- Identify all areas that contribute runoff
to the site.
Obtain soil data from soil and geological maps, aerial photographs, or site tests performed by soil analysts. Soil data deals with the horizontal and vertical extent of soil types, the elevation of the groundwater table, and the drainage characteristics of the soil.

The most important drainage characteristic of a soil is its permeability. Permeability limits the rate at which the rainfall infiltrates the ground, which greatly influences the presence and movement of subsurface water.

- Determine the general size and shape of
these contributing areas.

## Available Resources

- Determine the natural direction of surface-water flow, the slope of the land,
and the type and extent of natural ground cover.
- Locate natural channels that can be
used to move runoff within the project
Make an initial investigation of the time, materials, equipment, and labor available to build a drainage system. Without a sufficient quantity of these essentials, the construction of an adequate system is impossible.

## Design Procedures

Designing a drainage system involves dures in the design of any drainage strucnumerous assumptions and estimates. The ture:

Z Estimating the quantity of runoff.
degree of protection to be provided is directly related to the importance of the estab-
- Determining the area (usually in acres)
lished time-use period. The general locacontributing runoff to the facility tion of the facility will be determined by its functional requirements.

- Designing the drainage structure to
carry the maximum expected runoff.
The drainage system must be planned and designed for the predetermined location of the facility. There are three basic proce-

## Establishing Drainage-Structure Locations Determining The Area Contributing Runoff

When developing a tentative layout for the drainage system, identify all locations within the site requiring drainage structures because of topographical or manufactured features. This is best done from a topographic map of the area or a sketch of the project site.

The initial step in developing a drainagestructure layout is to establish the location of the required drainage structures. Placement, in general. will be controlled by the topography. For example, a fill section which crosses a valley will require one or more culverts to permit the flow of storm runoff down the valley. A depression or enclosed area will require ditches or culverts at various points to remove accumulated rainfall.

Next, determine the acreage of the areas that contribute runoff to these required drainage structures. An analysis of existing channels is helpful in establishing locations for the required structures. Upon completion, this tentative plan should be field checked at the project site.

should be as sible, Sharp straight and smooth as posbends in ditches or near culverts will cause erosion. Not shown on this sketch arc the standard ditches constructed along the sides of all military roads and airfields.

## Delineating Watersheds

After initially locating drainage structures, define the boundaries of the areas (or watersheds) contributing runoff to each of them.

This process is known as delineation.

Delineation is performed in six simple steps (refer to Figure 6-6): Step 1. Locate all existing or proposed drainage structures on the topographic map or sketch (X and V).

Step 2.

Identify and mark all terrain high points.

Step 3. Draw arrows representing water flow away from these high points. (These arrows must always be perpendicular to the contour lines because water flows downhill.)
Step 4. Continue drawing the arrows until they converge upon the culvert or the end of the ditch.

Remember that runoff will flow parallel to a road or airfield when it is intercepted by side (or interceptor) ditches.

Step 5.

Draw delineation lines. (These lines will run from high point to high point, indicating where the flow of surface runoff separates.) Delineation lines arc located so they cannot be crossed by any flow arrows. Flow arrows only cross delincation lines at culverts or ditches. NOTE: Delineation lines are drawn between opposing arrows, (See Figure 6-7.)
Figures 6-7 and 6-8 depict the use of flow arrows and delineation lines for special, manufactured structures such as roads, airfields, and superelevated roads.

When airfields or straight roadways are properly constructed, they arc shaped so that the highest portion of the cross section (the crown) is at the centerline, as illustrated in Figure 6-8. In the plan view, the delineation will be at the centerline precisely the curve.

where the accumulated storm water would will always separate at the outside edge of separate and flow in opposing directions.

Figure 6-8, page 6-13, shows how superelevated roadways (roadways that arc banked to ease the flow of traffic through a curve) arc delineated. In a properly constructed, superelevated road, storm water Several examples are provided to aid in visualizing special terrain features, includ -
ing hills, ridges, valleys, and saddles, as shown in Figures 6-9 and 6-10 and Figure 6-11, page 6-16.

Step 6.

have an multiple cover or Since each cover or soil type will measured according to its respective cover effect on the basin, if there arc type. (See Figure 6-12, page 6- 17.)
types of cover in the basin, each soil type must be delineated and Determining Drainage-System Size Counting-squares method. To make a hasty approximation of an area, transpose the outline of the watershed to graph paper (or other suitable grid). Count the number of whole squares and estimate the values of the partial squares Multiply the total num -
ber of counted squares by the number of counted square feet represented by a single square. Then convert the measurement in square feet to acres (1 acre = 43,560 square feet), Figure 6-13, page 6-18, shows this technique.

After delineating the watershed determine its size in acres. Make this measurement carefully, since the size directly influences the calculation of runoff from the watershed at peak flow. Use any accurate method of measurement desired. A planimeter which measures the area of a plane figure as a mechanically coupled pointer traverses the figure's perimeter, is quite accurate and should be used, if available. However, several other methods arc suitable for field estimation.

Solution: Step 1.

Step 2.

Step 3.

Geometric-shapes method. This method in-
volves estimating the watershed shape in
terms of rectangles, triangles, or trapezoids.
Using the formulas below for determining
the areas of these geometric shapes, deter-
mine the area of each shape and then total
all areas to estimate the area of the water-
shed.
      This technique is shown in Figure
6-14, page 6-20.

## Estimating The Quantity Of Runoff

**Rectangle:**

**Area = base x height or $A=bh$ Triangle:**

**Area = base x height or $A=bh$**
Drainage systems must be designed to accommodate the peak flow generated by runoff from contributing watersheds during the design storm, Many techniques arc available for determining the peak flow, but most arc too complex for general field use.

## 1 Introduction

The _mean-square_ of the _
This manual will demonstrate the most comon method for estimating runoffthe rational method.

## Designing Drainage Structures For Maximum Runoff

Stripper method. The stripper method is a variation of the geometric-shapes method. This method is shown in Figure 6-15, page
6-21. Approximate the area by drawing a series of lines that are equidistant (stripper width) across the delineated area.

Then measure the lines and total all of them.

L = total of the lengths, This method is more applicable for field estimations. Use a stripper width of 1 inch.

To accommodate the peak flow of the design storm, design structures must provide a sufficient cross-sectional area and longitudinal slope for passing storm runoff. If pending or flooding of adjacent areas must be prevented, the design must be for peak flow.

At the same time, water velocities generated at peak flow must not be so great as to cause damage to the drainage structure or excessive erosion and scouring 10 the protected facility.

The total of the lengths (L) is then multiplied by the stripper width. This would represent the total area on the map in square inches. Since the value of 1 square inch on the map would represent the map scale squared on land, the acreage can be found by multiplying L (in inches) x stripper width
(in inches) x (map scale in feel per inch and dividing the product by 43,560
acre.

Example:
Determine the capacity of drainage structures by calculating the runoff from all contributing drainage areas.

Specific procedures for designing open channels and culverts are discussed later in the chapter.

L = 12.5, map scale = 175 ft/in, stripper width = 1 inch (in)

## Estimating Runoff Using The Rational Method Estimating Principles

This is so close to unity that no correction factor is added; hence, the name rational (because a rational conversion of units] is used.

## Formula Variables

The rational method is used to estimate the expected peak storm runoff at a given drainage basin outlet. Much of the input to the formula is based on judgment. Therefore, it is imperative that sound engineering judgment be used to determine the input data.

The rational formula has three variables.

The C and I variables are explained here.

The A variable is explained later in this chapter.

## Assumptions The C Variable

The rational method is based on the following underlying assumptions and limitations:

- The area is not greater than 1,000 acres
and is regular in shape, with a homogeneous cover and soil type.
The runoff coefficient, or C variable, accounts for losses from precipitation. The C
variable is the decimal fraction of the amount of water expected to run off relative to the amount of precipitation. It can be expressed as the ratio

Z The entire drainage area is contributing
runoff to the outlet point when peak
runoff is obtained.
- The design rainfall intensity is uniform
over the entire drainage area (that is,
the rainfall is uniform over time and space).
- There are no active streams draining
the area. (If an active stream drains the
basin, use the hasty method found in FM 5-34.)

## Formula

Table 6-1 gives conservative values of C.

Knowledge of an area's USCS classification (for example, GMd) or an estimate of the soil's perviousness allows selection of a C
value.

C values appear in the table for manufactured surfaces and for wooded areas as well. An area of SP soil (a pervious, sandy soil with a slope less than or equal to 2 percent) with turf has a C factor of 0.10; that is, only 10 percent of the rain falling on this soil will actually run off.

The rational method uses the following formula:

Q = CIA
where

Q = C = I = A =
peak runoff in cfs runoff coefficient intensity of rainfall in in/hr drainage area in acres The following conversion factor is applied to this formula:

## 6-22 Drainage Solution: C For Nonhomogeneous Areas

The remaining 90 percent becomes lost to runoff through infiltration and other factors. At the other extreme, an asphalt pavement has a C value of 0.95. Only 5 percent of the rain falling on asphalt will be lost. The remaining 95 percent is expected to become runoff.

One of the assumptions made by the rational method is that there is a homogeneous cover and soil type throughout the area.

Quite often this is not the case, especially in areas where humans have exerted their influence on the topography.

NOTE: C values given in Table 6-1 are
actually maximums of ranges of allowable
values for the cover or soil categories.
Using the maximum value, a conservative
"worst-case" design runoff is calculated.
To use values less than the maximums
given in the table, refer to a reliable civil
engineering text dealing with hydrology.
The table is arranged with three columns
for varying slope conditions.

## C Versus Slope

If one type of cover and soil predominates in 80 percent or more of the area, the area is called simple and the C value for that predominant soil and cover type controls. If no one type of cover and soil type predominates in 80 percent or more of the total area, the area is complex and the C
value must be weighted; that is, the C value has to be adjusted to account for the proportion of C contributed by each subarea.

As terrain becomes steeper, water flows sooner and more rapidly. This allows less time for infiltration to occur and results in the C value becoming larger for the natural cover or soil categories. For this reason, whenever the average slope of an area exceeds 2 percent, an adjustment must be made.

Table 6-1 is arranged with three columns for different slope conditions and their corresponding runoff coefficients, Use the column that corresponds with the average percentage of slope.

To help understand this, imagine a complex area with one subarea of average turf and the other of bare soil. The slope of the bare soil does not affect how fast (or slow)
the water runs off the turfed area and, as a result, how much of the water soaks into the turfed area. The converse is also true.

The slope of the turfed area does not affect the speed or amount of water that runs off the bare soil area. Table 6-1 shows C
values with and without turf.

Weight the C value by multiplying the corrected C values by the area (in acres) that the C values affect. Then total the products and divide by the total acreage.

Expressed mathematically, the formula is
The C for a turfed soil is different from the C for bare soil. The turf (grass or other ground cover) exerts a drag on water, causing slower flow and providing more time for infiltration to occur; hence, a lower C
results. Denuded soil (soil from which the turf or cover has been removed) requires an increased C because a swifter flow will result and less time will be available for losses to occur.

If one cover type has more than one flow path, average the slopes and use the appropriate column in Table 6-1.

where
Example:
Flow path 1A = 2.3 percent and flow path
1B = 1.9 percent.

  C value and area for first subarea C value and area for second subarea

## The I Variable If A 30-Minute-Duration Storm Sweeps Over

As explained previously in this chapter, rainthe same area in a uniform fashion, the enfall intensities can be determined from pinpoint source data or isohyetal maps. The former method provides more accurate results if reliable data is available. The task of calculating the critical duration for any given drainage area is detailed here.

## Time Of Concentration

tire area contributes runoff to the outlet in the 30-minute time frame (the TOC mentioned above).

If a storm with a duration longer than the TOC occurs, the drainage designer can easily picture (using the standard intensityduration curve) that the intensity, I, will be less than the I of the 30-minute storm. Examination of the rational-method equation, Q = CIA, reveals that since C and A would not change as I decreases, Q must decrease as well. The critical-storm duration which yields the design Q must then be equal to the contributing area's TOC.

## Determining Toc

Under the assumptions listed at the beginning of this section and with the intensityduration relationships presented earlier, only one particular storm will give a maximum discharge (Q) for a given area. This particular storm is the one that rains over the entire area being drained for a period of time just long enough to fill the outlet with runoff from all segments of the area at the same time. This time is called the area TOC. A storm of shorter duration than this TOC would not last long enough for the runoff from the more distant segments of the area to reach the outlet. The outlet woulrd be filled only with the runoff from nearby segments. Therefore, runoff would not be maximum Determine the area TOC by determining representative flow paths. A flow path is the path that a typical drop of water will follow from the time it hits the ground until it reaches the area outlet, The flow path is called representative, because not all drainage areas are as regular in shape as the area in Figure 6-16. The path selected must be representative of the time at which most of the area will be contributing water to the outlet point. Establishing representative flow paths is based largely on experience and judgment (trial and error).

In Figure 6-16, all of the area below the 10-
minute line will drain in 10 minutes or less. Runoff from the area between the 10-
and 20-minute lines will reach the outlet in not less than 10 minutes but will have drained in not more than 20 minutes.

Similarly, the runoff from the area between the 20- and 30-minute lines will reach the outlet in not less than 20 minutes nor more
[ban 30 minutes. At the end of 30
minutes the entire area is draining. Therefore, the TOC at the outlet for this area is
30 minutes.

If a storm of 20-minute duration sweeps over the area in a uniform fashion, only a fraction of the total area inside the 20-
minute boundary simultaneously contributes runoff to the outlet at the end of the storm. All runoff from the upper third of the area reaches the outlet after the rainfall has ceased and after much of the lower acreage has finished contributing runoff.

## 6-24 Drainage

page 6-9, shows that the I for a 40-minute storm is 2.7 inches per hour; therefore, the estimated runoff is

Q = CIA Q = (1.0)(2.7 in/hr)(100 acres) = 270 cfs
A storm of 30-minute duration will have an intensity of 3.2 inches per hour. At the end of 30 minutes, 90 percent of the area
(90 acres) will be contributing water to the outlet and the volume will be

Q = CIA Q = (1.0)(3.2 in/hr)(90 acres) = 288 cfs
which is larger than the 270 cfs estimated for the entire area.

Unlike the area depicted in Figure 6-16, the area in Figure 6-17 is irregular as most natural areas will be, In irregular areas, it is especially critical that the flow paths chosen truly represent the time required for most of the area to drain. All the area below the 10-minute line will drain in 10 minutes or less. The area between the 10- and
20-minute lines will drain in not less than
10 minutes nor more than 20 minutes and so forth up to the 40-minute line. Flow lines a, b, and c have been determined; 90
percent of the total area (90 acres) lies below the 30-minute line and will drain in 30 minutes or less. Water from the remaining
10 acres will reach the outlet in not less than 30 minutes nor more than 40 minutes. Flow lines a and c should be chosen as the representative flow paths and used to determine the TOC because they are indicative of the time it will take for most of the water from the area to reach the outlet, Line b is not representative. For simplicity, in this example let C arbitrarily equal 1.0 and assume that the 1-hour, 2-
year intensity is 2,0 inches per hour. If a
40-minute-duration storm occurs, in 40 minutes the entire area will be wet and contributing water to the outlet point, The standard intensity-duration curve in Figure 6-4, Flow paths must be chosen that represent the time required for most of the area to drain. As shown above, a shorter storm of higher intensity may cause a larger flow. After all the chosen paths have been timed, the times should correspond to each other within a few minutes. If times are not relatively close, make a careful check to determine why, and assess the area to determine which of the times will produce the critical flow. Apply rainfall adjusted to this critical duration over the entire watershed. The design runoff from the watershed in Figure 6-
17 would be

Q = CIA Q = (1.0)( 3.2 in/hr)(100 acres) = 320 cfs
After representative flow paths have been established, estimate the time it will take for water to reach the outlet if it travels along the established path. To do this, determine (through observation) the nature of the surface cover and the slope of the flow path. Slope affects the velocity of the water in that the steeper the slope, the faster the water runs. Water will also travel faster across a paved area than across a grassy area of the same slope because grass slows the flow. Flow is slower over bare soil than over pavement but faster than grass. Flow in a ditch is more rapid than overland flow over turfed, bare, or compacted gravel surfaces.

Estimating Flow Time for Single Covers Notice that there is a series of curves, each After establishing the location, the cover, with linear and curvilinear portions. The and the slope of a flow path, Figure 6-18
slope of the curve indicates the velocity at a can be used to estimate the travel time given point along the flow path. In the curalong the flow path.

It is important to unvilinear portion, the slope is initially zero derstand what the illustration is depicting and gradually steepens until it becomes as well as how to use it properly.

linear. This represents the fact that water

Travel
Path
Cover
Length
Slope
Time
(ft)
(%)
(rein)
1
Sparse
800
3,0
19
turf
2
Paved
500
1.5
8
area
3
Average
600
2.5
26
turf

initially moves very slowly and begins to pick up speed only as its accumulated depth increases. It is initially slow flowing in a laminar or sheet-flow manner and gradually becomes turbulent (and faster) as it progresses downhill. At some point, the turbulent-flowing water reaches some steacly-state velocity. It is apparent from Figure 6-18 that the slope and "slickness"
of the flow path dictate how quickly the transition occurs from slow-moving laminar flow to rapid, fully developed turbulent flow Note that it was necessary to interpolate to find the travel time for path 3. It is valid to interpolate between labeled lines, but never extrapolate above or below the limiting-curve values. Use the limiting curve in that situation To estimate the travel time in ditch-flow conditions, usc Table 6-2. Using the slope of the flow path, enter the chart, then read the right-hand column under velocity. To calculate the velocity, divide the length of the path by the velocity obtained from the chart.

Example:
Path 1B
To estimate the travel time in sheet-flow conditions, use Figure 6-18. Enter the right-hand vertical edge at the appropriate cover type of the flow path. Proceed horizontally to the left until reaching the curve labeled with the slope of the path.

Follow the curve up or down until you reach the intersection of the horizontal line equaling the flow-path length, which is determined on the left-hand vertical edge. Read the travel time, which is found by drawing a line vertically from the intersection to the lowermost axis. Some examples of the use of this graph are as follows:

Cover - Ditch
Length - 1,015 ft Slope - 0.9%
Chart velocity - 135 feet per minute (fpm)

Solution:
Arid partial travel times to get the total travel time:
= 7.5 minutes (min)
Travel time = 19 min + 3.0 min = 22 min

## Estimating Flow Time For Multiple Covers

It may be helpful, at times, to estimate the travel time through a culvert. A reasonable assumption of culvert velocity is 5 feet per second (fps) (300 fpm), although more precise determinations can be made with information presented later in this chapter.

## Selecting Design Toc

In many cases, a flow path traverses more than one cover type. Estimating travel time accurately then becomes more complicated because it is not appropriate simply to add times obtained from Figure 6-18, page 6-26. Laminar flow occurs only once along a flow path, no matter how many cover types are traversed.

For subsequent covers, it becomes necessary to estimate flow velocity using Table 6-2, page 6-27.

To estimate travel time in a ditch, use Table 6-2. Enter the table using the slope of the flow path. Then read right to the velocity column and find the velocity in feet per minute. By knowing the flow-path length and the table velocity, the travel can be calculated.

Example:
The usual procedure is to establish several trial flow paths that are thought to be representative of the area and determine a travel time for each path.

Compare the time for water to travel along each of the flow paths chosen.

If the times arc within a few minutes of each other, select the longest time as the area TOC. If the times arc not within a few minutes of each other, make a complete analysis of the area. New flow paths may be needed to determine which of the times is representative of the bulk of the area draining. The largest representative time is chosen as the design TOC.

## The A Variable

Assume that paths 1 and 2 from the preceding example were actually the upper and lower lengths of one combined flow path. To estimate their combined travel time, first estimate each separately in the order the water would flow through them.

The drainage area, A, (the area contributing storm-water runoff to the culvert or ditch being designed) must be calculated in acres, This procedure was presented earlier in this chapter.

Solution:

## Applying The Rational Method

Application of the rational method of estimating drainage varies according to the type of drainage area. One type is a single, independent area which does not receive any drainage from an upstream area. Another type is a dependent or successive area that receives runoff from another area.

Estimate the travel time of path 1. Since path 1 is uphill from path 2, nothing has changed from before. The travel time remains 19 minutes. Estimate the travel time of path 2.

Remember that the flow entering at the upstream end of path 2 is al ready moving.

To estimate travel time, divide the length of the path by the estimated velocity listed in Table 6-2. In this case, for a 500-foot, paved path at 1.5 percent

## Single Areas

Travel time =
The rational method of estimating single areas is reasonably simple and straightforward, if it is done methodically. The steps are summarized in the proper order.

lf this summary is followed step-by-step,
(Note that path 2 had an 8-minute travel time when considered alone.)
the procedure will be correct and the estimate obtained will be as valid as the judgments that are made.

Step 8. Determine the average slope of the basin or each subarea based on flow paths.

Define the slope as being either   2%, > 2%
and < 7%, or    7%.

Step 1.

Delineate the area to determine the area contributing runoff to your project location. Refer to page 6-13, Delineating Watersheds.

Step 2. Delineate subareas by soil or cover type. Refer to page 6-15.

Step 9.

Find the C value of the basin or each subarea based on soil or cover type and slope from Table 6-1, page 6-22. Select C from the appropriate column in Table
6-2, page 6-27, making sure that you pick the right C-value column. Notice that the columns are arranged with respect to slope and cover type.

Step 3. Determine acreage for each basin and subarea.

Refer to page 6-17.

Calculate      if the area is complex.

Step 4. Classify the drainage basin as simple or complex.

A simple watershed has one cover or soil type over 80 percent of its total area. A complex watershed has no single cover or soil type covering at least 80 percent of its total area.

Step 10.

Determine the travel time for each flow path and select the longest flow path as the basin TOC. Refer to sheet flow on page 6-27 and ditch flow in Table 6-2.

Step 5. Determine representative flow paths. Refer to the information on pages 6-24 and 6-25.

Find I for a 2-year, 60-minute the world isohyetal map (Figure
6-7).

Step 11. storm on 6-3, page Step 12.

Adjust I based on the TOC (step
10), using Figure 6-4, page 6-9.

Step 13. Calculate Q using C from step 12, and A from step 3 as follows: Q=CIA.

## Example:

Estimate the amount of runoff expected to arrive at the culvert in Figure 6-19, page 6-30.

The location is Giessen, Germany, and the design life is two years.

NOTE: A number of steps, quantities, and calculations will be "given" to illustrate the process.

Solution:
Step 6. Divide flow paths into two sections:
laminar and ditch flow. As a rule of thumb, use 500 feet plus or minus 200 feet as a point where laminar flow will change to ditch or steady-state flow. Generally, overland flow concentrates into natural rivulets or channels after roughly 500 feet of travel. This distance may vary up to several hundred feet either way, depending upon such factors as soil type, vegetation, and slope, It is always best to visually investigate on-site to look for evidence of channeling, and take measurements accordingly.

However, since in this problem it is not possible to visually investigate the drainage area, clues to determine when overland flow
(sheet flow) ends and ditch flow begins must come from topographic information alone. Some of these clues may be the beginning of uphill swales or flow paths that converge in a swale.

This convergence may take place in a valley where multiple paths meet.

Step 1.

Delineate the area. (Given for this example. )
Step 7. Determine the slope of each section of flow path. See page 6-25.

Step 2. Delineate the subareas by soil or cover type. (Given for this example.)
Step 4. Classify the drainage basin as Step 3. Determine the acreage for each simple or complex.

Divide the largest soil basin or subarea.

The following acreage is or cover group (the GMd soil] with turf subgiven for this example:
area equaling 47.9 acres by the total area,
48.8 acres.

Average turf GMd
47.9 acres
Compacted gravel
0.9 acre
Total acreage (A)
48.8 acres

## 6-30 Drainage

Since the percentage is greater than 80, this area will be treated as a simple area consisting of 48.8 acres of turfed GMd soil.

an average slope, the number of slope measurements taken on the western slope should be balanced by twice that number taken from the east. Figure 6-20 reflects this guideline, showing three slope measurements, two on the east and one on the west.

NOTE: The selection of representative
flow paths is a judgment call based on
the best evaluation of the topographic fea-
tures.

Step 5. Determine the representative flow paths. It is necessary to determine the average slope of the entire simple area shown in Figure 6-19. In order to do this, use representative flow paths, If the north -
south running swale is imagined as the dividing line, approximately one-third of the watershed area lies to the west (left) and two-thirds to the east (right). To determine Step 6. Divide flow paths into two sections:
sheet and ditch flow. Generally, overland flow concentrates into natural ditches after
500 feet. Path 1 changes to ditch flow in the valley where it slopes down. See section A of Figure 6-20, page 6-31. The same is true for path 2. By looking at the contour lines near path 3, we can see they are relatively flat.

Flow occurs across a wide area, and no clear point can be seen where the flow changes.

A good estimate would be at 575 feet.

The slope of the original path 3 is unchanged, remaining at 3.6 percent. Paths
2A and 2B are now one single path, 2, with an average slope of 2.3 percent. (The average of 5.2 percent and 0.8 percent is not 2.3 percent.) Redetermine the overall slope (as done earlier). The earlier path 1B has been deleted, leaving only the original path 1A (with S = 5.9 percent) as the new path 1. The reason for deleting 1B is that it provides the same information already provided by the new path 2. Path 2B could have been deleted instead of path 1B with no change to the final result.

Step 8. Determine the average slope of the basin or subarea based on flow paths. With the three flow paths now determined, the average slope of the simple area is
Step 7. Determine the slope of each flow path. The representative flow paths selected in an earlier step, if properly selected, can provide very good slope information with a minimum of effort. Other slope lines may be selected for practice and to gain confidence in using this procedure.

Remember to maintain the 2-to-1 balance in finding slopes in this basin and to delete redundant information. The slope must be measured over a path that water would actually follow as it flows downhill. Normally, all work would be performed on one consolidated map.

For instance, to determine the slope for path 1A
Step 9.

Find the C value of the basin or subarea based on soil or cover type and slope from Table 6-1, page 6-22. Since we know that the average slope is 3.93 percent, we can use Table 6-1. Using the column marked slope >2% and <7% with turf, we have a C value of 0.35.

This procedure is repeated for every flow path illustrated in Figure 6-20.

A tabular solution is recommended to determine TOC.

Length
Slope
Time
Path
Cover
(ft)
(%)
(min)
1A
Average
575
5.9
14.5
turf
1B
Ditch
1,015
0 9
7.5
section
(135 fpm)
22.0
2A
Average
640
5.2
16.5
turf
2B
Ditch
1,285
0.8
9.9
section
(130 fpm)
26.4
3A
Average
575
5.0
16,0
turf

Step 10. Determine the travel time of each flow path and select the longest flow-path travel time as the basin TOC. Times for paths 1B and 2B were obtained by dividing their flow lengths by approximate velocities obtained from Table 6-2, page 6-27. The travel times for each of the complete flow paths (22.0, 26.4, and 19,02 minutes, respectively) are obtained from Figure 6-18, page 6-26.

The variation between the smallest and largest time, although not small, is not excessively large, either. Perhaps path
1 is not representative and some ditch flow occurs along path 3 that could not be determined from the topographic information available. Both of these possibilities are likely to be true.

However, without an actual field investigation to justify revising either path 1 or 3, accept the travel times already determined and select the largest as the basin TOC. Thus, TOC = 26.4 minutes.

3B
Ditch
650
2.3
3.02
section
(215 fpm)
19.02

value for each soil or cover must be determined based on the average slope for each cover area. Once all C corrections are made, then an area-weighted C or     can be determined.

     would be used in solving Q = CIA.

## Successive Areas

Step 11.

Determine the I value for a 2-
year, 60-minute storm. To determine factor I, a source of rainfall data is necessary.

The choice is between using pinpoint data
(the most accurate means of determining 1)
or referring to an isohyetal map. Since pinpoint data is not available, use an isohyetal map. Refer to the isohyetal map in Figure 6-3, page 6-7. Knowing that the airfield is located near the demilitarized zone (DMZ) in Korea, as shown in Figure 6-3, rainfall intensity of the 1-hour, 2-year storm is determined to be 2.5 inch per hour or
Up to this point, the drainage areas discussed have been single, independent areas, whether simple or complex, These independent areas do not receive runoff from an upstream area. Some drainage systems, however, consist of a series of drainage areas with upstream areas discharging runoff into lower areas. The areas receiving this runoff are called dependent areas. The runoff accumulates and increases in its passage through the system. Sometimes, two or more areas discharge runoff into the same dependent downstream area. Such contributing areas arc called parallel areas.

Step 12. Adjust the I value. To determine I,       must be adjusted so that its duration is equal to the basin TOC, 26.4
minutes.

Use the set of standard intensityduration curves in Figure 6-4, page 6-9, to make the adjustment. Using curve 5 (for
2.5 inches per hour) and sliding along until the 26.4-minute imaginary vertical line is in tersected, the intensity (adjusted to 26.4
minutes) is found to be 4.2 inches per hour; thus-- Step 13.

Calculate Q using C from step 9,
     from step 12, and A from step 3.

All the variables have been determined to solve the equation *Q = CIA,* as follows:
Unfortunately, the increase in runoff is not the simple summation of the peak runoff of each individual area. The individual peak flows arc acted upon by various factors, including storage and peak-tlow reduction while in the drainage network, Also, the peak flow from upstream areas and the peak flow from downstream, dependent areas will probably not arrive at the lower outlet simultaneously. Hence, the total peak flow must be less than the total of the individual peak flows.

## Calculating Toc

C = 0.35 I = 4.2 in/hr A = 48.8 acres Q = 0.35 x 4.2 in/hr x 48.8 acres Q = 71.74 cfs
or 71.7 cfs of Q is the final solution The determination to the example.

If area 5 had been a complex area, steps 1,
2, 3, and 5 would be unchanged. The only difference would occur in step 4, which would be changed as follows:
Because of the accumulation of peak flow in successive areas, calculation of TOC for those areas must be different from the method used for single, independent areas.

To estimate the amount of the accumulated runoff with some precision, a procedure has been developed to recalculate TOC for each of the successive drainage areas as water travels downstream. Naturally, as TOC increases, rainfall intensity, I, decreases.

Step 4 (for a complex area). An    for each soil or cover area must be determined
(except for manufactured covers). A C
The term *TOC* must be modified to reflect calculation differences. Consider two areas, an upstream area W and a downstream area X, as shown in Figure 6-21. The maximum travel time from the most hydraulically remote represen [alive points in this series of two areas to the outlet of area X is defined as TOC. The maximum representative flow times for runoff originating in both areas (X and W) to arrive al
[heir respective outlets (X and W) arc defined as inlet time X and inlet time W, respectively.

To a designer engaged in sizing the culvert which serves as outlet W, the TOC would simply be However, when sizing culverts that occur further down in successive areas (for instance, the culvert at outlet X), the designer requires the time it takes water to arrive from the most hydraulically remote location, which might be in either area X or area W. To determine this maximum representative time     the designer must compare the travel times for runoff origination in both areas.

The TOC at teh outlet upstream in area W
is given as       which equals inlet time W for this independent area. The' ditch time
(DT) or transit time through area X, from outlet W to outlet X, is         The total of these two elements


is inlet The travel time for waler originating in area W and arriving at outlet X is equal 10 the inlet lime at area W (which is the same as
      since area W is dependent) plus the transit time as the water flows in a ditch through area X.

This composite time, called inlet       must be compared to the time for water that originates in area X, or inlet             ,    the maximum representative time for water to arrive at outlet X, is the larger time value identified in the comparison.

## Estimating Successive Area Runoff

The modified definition of TOC is applied in estimating runoff for successive areas. This calculation requires collection of certain essential data and application of the principles used for single areas, appropriately modified, to determine the desired Q.

Preparatory Work.

Step 1. Delineate every subarea in the series of areas. Step 2.

Determine the intensity of the 2-
year, 60-minute rainfall.

Step 3. Determine A, C, and inlet time. For each subarea, deter,ome the acreage (A); variable C, corrected for slope and weighted (as necessary); and the inlet time.

Step 4. Determine the DT (or transit time). For each dependent subarea, the DT is determined from the upper outlet 10 the Example:
lower outlet fpm, unless using culvert flow (assume 300
you have more precise data).

Determining Using the rational method and Figure 6-22, page 6-36, determine the runoff, in cfs, expected at culverts 3 and 4 at the Span II Army Airfield at Giessen, Germany. The soil type is GMd.

Specific Q, Working systematically, start at the uppermost subarea and proceed downstream. Refer to Figure 6-21
and note that subarea W is upstream from subarea X.

Solution:
Step 1. Determine the subarea TOC using these simple rules:
Step 1.

Delineate the area; it is found to have the following:
The rule for an independent subarea is

Subarea A.

The rule for a dependent area is

Compacted gravel
6.2 acres
Simple
Average turf
0.2 acre
Area
6.4 acres
Subarea B.
Compacted gravel
0.9 acre
Simple
Average turf
12.5 acres
Area
13.4 acres

Compare inlet      with inlet time Select the larger value of      based on the comparison.

Step 2. Delineate subareas by soil or cover type. (See step l.)

## Step 2. Adjust

Step 3. Calculate Q for subarea W.

is given in Step 3. Determine acreage for each basin or subarea. (This information step 1,)
simple or com-
Step 4. Classify the basin as plex.

Step 4.

Proceed downstream to subarea X
and repeat steps 1, 2, and 3.

Subarea A.
Compacted gravel
6.2 acres
Average turf
0.2 acre
Simple
Total 6.4 acres

Step 5.

Total the accumulated runoff, To get the total runoff at the Outlet of subarea X, use the following equation:
6.2 acres/6.4 acres = 0.97 or 97%

Subarea B.
Compacted gravel
0.9 acre
Average turf
12.5 acres
Simple
Total 13.4 acres
12.5 acres/13.4 acres = 0.93 or 93%

Step 6. Continue working downstream.

Proceed until the runoff at the lowest outlet in the series is calculated. Use the drainage basin's corresponding rainfall in -
tensity for the I value; use the total area for all basins and the subareas for the area. A
value, in the rational-method formula.

Step 5. Determine representative flow paths. See Table 6-3, page 6-37 (given information).

Step 6. Divide flow paths into two sections: sheet flow and channel flow. See Table 6-3 (given information).

NOTE: Remember that when using the ra-
tional method, the area limit is 1,000
acres. Always check the accumulated
acreage to ensure that it does not exceed
1,000 acres.

Step 7. Determine the slope of each sec-
Both of these paths will have an average tion of the flow path.

slope of less than 2 percent. Subarea 2 has three major paths. Path 2 has an Step 8. Determine the average slope of the average slope of 2.3 percent, path 3 has an basin or each subarea, There are two average slope of 2.4 percent, and path 4
paths in subarea 1, paths 1A and 1B.

has an average slope of 2.6 percent. (See

## 6-36 Drainage

Subarea A.

Figure 6-22. ) Using this information, we can now get an average slope for paths 2,
3, and 4.

Subarea B.

Average Slope =
Compare inlet      = 25.3 min with
         + DT = 16.3 + 3.8 = 20.1 min
Average slope for subarea 1 = < 2%
Average slope for subarea 2 =  2.4%
Select the larger value of      = 25.3 min
and       = 1.8 in/hr

Step 12. Adjust I based on TOC using Figure 6-4, page 6-9.

(This step was included in step 11.)
Step 13. Determine runoff.

Step 9.

Find the C value for each subarea, Subarea A has compacted gravel with an average slope less than 2 percent. Using Table 6-1, page 6-22, we find that the C value is 0.70. Likewise, the C value for subarea B, GMd with average turf with a slope of 2.4 percent, is 0.35.

To calculate runoff in subarea A, use
= 0.70( 2.6 in/hr)(6.4 acres) = 11.6 cfs To calculate runoff in subarea B, use
Step 10.

Deter mine the travel time of each flow path and select the longest flow-path travel time as the TOC. Obtain sheet-flow times from Figure 6-18, page 6-26, and ditch-flow travel time from Table 6-2, page
6-27. Determine the travel times and ditch time from Table 6-3.

\begin{tabular}{l l} \begin{tabular}{l l} $\text{Ditch~{}time}_{3.4}$ & = \\  & = 3.8 min \\ \end{tabular} . &
\begin{tabular}{l l} $\text{= 0.35( 1.8 in/hr)(13.4 acres)}$ \\ $\text{= 8.4 cfs}$ \\ $\text{= 11.6 cfs}$ \\ $\text{= 11.6 + 8.4 = 20 cfs}$ \\ \end{tabular} \\ \end{tabular}

NOTE: Although path 4 was used to ob-
tain an accurate slope average, it is not
used for travel time. The situation, as
drawn on the map, clearly shows that
path 4 could not be chosen for the TOC.

Step 11.
          Determine I and      (I value for
Giessen, Germany is 1.7 in /hr from local
rainfall records.)

## Section Ii. Open-Channel Design

An open channel is a conduit with a free-
The size, the shape, the method of construcwater surface used to convey water. The tion, and the location of a ditch are determost common is a ditch, which is an open mined largely by its purpose. These facchannel cut into the soil. If so desired, the tors, once determined, will influence the ditch can be lined along the bottom from design capacity and maintenance requirebank to bank.

ments.

## Design Factors Location

There are three main types of ditches used in road and airfield construction.

motor grader and the wheeled tractorscraper. Other items of equipment that can be used to excavate a ditch section include the backhoe; bulldozer; front-end loader; trenching machine; and crane equipped with a dragline, clamshell, or shovel front.

An *interceptor ditch* is generally located on a hillside above a roadway or other feature requiring protection.

Its function is to intercept runoff and direct the flow to a more desirable location.

It is usually located above sidehill cuts to prevent erosion of the cut. A side ditch is located along the side of a road. It collects runoff from the road and adjacent areas and transports it to a culvert or diversion ditch.

When the Topography allows, a diversion ditch is built to transport water away from roadways or airfields. It can be used in conjunction with interceptor and side ditches to transport water between culverts or to divert an existing stream channel around a project.

## Cross Section

The location and peak quantity of runoff expected will determine the ditch cross-sectional area required. The most common shapes of cross sectionstriangular (symmetrical and nonsymmetrical), trapezoidal, and segmental-are shown in Figure 6-23.

In the TO, the shape of a ditch is also dictated, to a great extent, by the choice of engineer equipment available for its construction. Two items of equipment are uniquely suited for speedy ditch excavation: the

## 6-38 Drainage

equally, the ditch is called symmetrical.

Nonsymmetrical ditches have side slopes that differ.

However, production rates for these items are relatively low compared to the grader or scraper; hence, the grader or scraper is more likely to be used.

Triangular or V ditches are commonly installed to handle flows up to 60 cubic feet per second. The road grader is well designed to quickly excavate the necessary cross section to handle this flow, provided that the ditch is built in soil rather than rock. Grader efficiency drops significantly when cross sections of larger dimensions are required.

The designer selects appropriate side-slope ratios. The selection is critical to ensure that the ditch serves its purpose. Ditch sidewalls that are too steep invite excessive erosion and are likely to cause the ditch to clog with sediment.

Even more serious is the risk of a severe accident, if a vehicle should run into the ditch and become entrapped or overturn because the side slope is too severe. Only one side slope is required for symmetrical ditches. For clarity, the terms front slope or ditch slope and *back slope* are used to differentiate between the dissimilar slopes. Figure 6-24, page 6-40, illustrates this terminology.

For flows larger than 60 cubic feet per second, the *trapezoidal ditch* is commonly specified.

The flat bottom and midsection of this ditch can be excavated rapidly by a wheeled scraper, and the side slopes can be dressed back by subsequent passes of a road grader.

The sidewall of a roadside ditch located adjacent to the shoulder is called the front slope of the ditch. The far slope, called the back slope, is simply an extension of the cut face in an excavation.

The following rules of thumb are applicable only in shallow ditches in relatively flat terrain:
Smaller bottom widths can be provided using any of the previously mentioned items of construction equipment, including the road grader with its blade turned to a high angle.

Production rates, however, will be much lower than those of the wheeled scraper.

Z Roadside ditches may be cut nonsymmetrically at 3:1/1:1 (front slope/back slope).

NOTE: For calculation purposes, the
horizontal component of the roadside
ditch will be referred to as X. Likewise,
the horizontal component on the back
slope will be referred to as Y. (See Figure
6-23.)

Note that the 60 cubic feet per second
guideline is flexible. If scrapers are not
available to excavate a ditch carrying 100
cubic feet per second but a grader is, com-
mon sense dictates that the grader be used
to construct an oversized V ditch rather
than using low-production-rate equipment
to construct a trapezoidal ditch,

- Diversion ditches may be cut symmetrically at 1:1.
Z Ditches intended to be subject to cross
traffic may be cut symmetrically at 3:1
or more gently.
The *segmental-ditch* shape results when explosives arc used to create the ditch. This technique is often used when the terrain is too soft to support excavating math inery. Ditches cut by hand will often bear this shape as well.

## Side-Slope Ratios

In most cases, interceptor and diversion ditches are installed far enough from the traveled way not to present a hazard to passing vehicles on the roadway or aircraft on the runway. Since there is very little danger from either side, symmetrical sideslope ratios are specified for these types of ditches.

Ditches have two sides and two associated side-slope ratios. Side slope is the slope of the banks of the channels, normally expressed as a ratio of feet horizontal to feet vertical.

For example, 3:1 is a side slope of
3 feel horizontal to 1 foot vertical. When the sidewalls on opposite sides are inclined Tables 6-4 and 6-5 are also useful in selecting front slopes for fill sections.

## Types Of Flow

A *uniform* flow is assumed when the depth of water throughout a channel is constant in dimension and slope. This means that the slope of the water surface is the same as the slope of the channel bottom. This assumption is essentially correct for channels of moderate slope and length. Flows in ditches, canals, and rivers are uniform, but flows over spillways or waterfalls are not uniform.

Several types of flow are associated with open channels.

Some of these types occur simultaneously in the same channel. An understanding of these types of flow and their interrelationship is essential to the effective design of drainage systems.

The strength of viscosity forces and hence the thickness of moving fluid, determine whether channel flow is turbulent or laminar.

An *open-channel flow* has a free surface and no hydraulic pressure. Some examples of open-channel flow include ditches, canals, streams, and culverts not flowing full. Empirical formulas with experimentally derived coefficients are used in designing an open channel.

These hydraulic formulas reflect certain hydraulic theories and assumptions governing design analysis of free-flow channels.

Turbulent flow is assumed for purposes of open-channel design. This type of flow occurs when viscosity forces are relatively weak and the individual water particles move in random patterns within the aggregate forward-flow pattern.

A *steady flow* is assumed in an open channel with a uniform depth during the design period. Changes in flow are generally slow, and any errors that may be introduced by this assumption are not significant.

A continuous flow is assumed according to the principle of the conservation of mass.

Laminar flow occurs when viscosity forces predominate and the particles of the fluid move in smooth, parallel paths. An example of this type of flow is honey poured from a container; honey has high-viscosity strength compared to water. The only type of laminar flow considered in this manual is sheet flow, which occurs where depth is extremely shallow. It is assumed that the flow in natural and designed channels will be steady, continuous, uniform, and turbulent.

Manning's equation can easily be solved mathematically using the equation. However, to assist in the design of open channels, the equation has been prepared as a nomograph. (See Figure 6-25.)

## Design Equations For Open Channels Roughness Coefficient (N)

This section deals with open-channel design equations.

Because of the variables and assumptions to be made, trial techniques are required to determine the shape and depth of a particular channel before a final solution is reached.

Continuity Equation The equation of continuity is expressed as follows: where
The roughness or resistance coefficient is a measure of the resistance to flow caused by surface-contact irregularities. It varies with soil type, channel condition, and type of ditch lining used.

Use Table 6-6 to estimate the roughness coefficient, n, used in the solution of the equation. The coefficient can be changed only if the ditch lining is changed or modified. The effect of the roughness coefficient on velocity can be altered by changing the side slopes of the ditch, thereby changing the water con tact area. Changing the roughness coefficient in this way changes the ditch capacity.

* = rate of flow in cfs
* = cross-sectional area in sq ft
* = velocity in fps

## Longitudinal Slope Or Grade (S)

Manning's Velocity of Flow Equation Many empirical equations have been proposed for determining turbulent flow. The most widely used is the equation presented by Manning in 1889. It states
or, after transposing, Under normal conditions, the ditch slope
(the longitudinal fall of the channel in feet per foot or in percentage) will be determined by the slope of the terrain. For short ditch lengths only, a variation from the natural slope of the terrain can be achieved by modifying the cutting depth of the ditch.

By varying the cutting depth within the ditch length, the slope can be increased or decreased independently of the terrain slope.

where

$V=$ velocity of flow in fps $R=$ hydraulic radius

or

cross-section area of water

$R=$ wetted perimeter
In channel design, slope percentage and the resulting change in velocity are important considerations. Slopes over 2 percent may have too high a velocity, resulting in erosion.

Slopes under 0.5 percent will generally have too low a velocity, resulting in sedimentation deposits. Deposition (the depositing of sediment on the bottom of the ditch) normally occurs at velocities below 3 feet per second.

## Velocity Of Flow (V)

S = slope or grade of the channel in feet per foot (ft/ft)
n = roughness coefficient or friction factor, which depends upon the material comprising the channel lining NOTE:
When using metric units
Many ditches with differing side slopes and cross-sectional areas of flow will carry the same rate of runoff on a similar longitudinal slope. In each case, however, the velocity of flow will be different. Since excessive velocity in a ditch will cause erosion and possibly damage adjacent structures, it
Z If velocity (V) increases, erosion inmust be contained within limits. Table 6-6
creases.

lists the maximum permissible velocities, depending on soil and other factors.

## Hydraulic Radius (R] Velocity Relationships

- As slope increases, velocity (V) increases.
- As quantity of runoff (Q) increases while
area (A) remains constant, velocity (V)
increases.
Z If Manning's n increases, velocity (V)
decreases.
The hydraulic radius (R) is the area of the water cross section of the ditch divided by its wetted perimeter, calculated as shown in Figure 6-26.

It relates the surface area of friction resistances with the volume of water being carried by the ditch. The hydraulic radius can be calculated using an electronic calculator as shown in Figure 6-
27, page 6-46.

## Design Considerations Slope (S)

The slope will be determined by the terrain.

In general, the slope used will be the natural ground slope. Small modifications of the slope can be made for short ditch sections.

There are certain factors known for each ditch being designed. Each of these factors will affect design details. Items such as the location, the peak flow or runoff carried, the effect of terrain on slope, and the soil type or material to be used to line the ditch all have a bearing on channel design.

## Proposed Ditch Lining Location

The ditch lining determines the velocity and roughness coefficient or resistance factor, n.

(See Table 6-6.)
The location of the ditch will determine its general shape and the side slopes to be used in its design.

## Quantity Of Runoff (Q)

Table 6-6 gives maximum erosion velocities for each type of soil and lining. The lower velocity on the chart indicates the velocity at which erosion will start occurring in some portion of the ditch. At the high velocity value, the entire length of the ditch will probably be eroding.

Table 6-6 also provides Manning's roughness coefficient (n) which represents the friction resistance of the ditch, channel, or stream for various soil types and linings. Use the average value of n for design purposes.

Designers must know the quantity of runoff the channel will have to carry. Usually, this is estimated using the rational method of runoff determination. However, it may also be estimated based on knowledge of the slope, the diameter, and the type of culverts used to discharge into the channel. The value of Q will also determine which type of ditch section, triangular or trapezoidal, will be used. This depends on whether Q is greater than or less than 60
cubic feet per second.

## Design Techniques

Once design considerations have been ex-
Step 1.

Determine the peak volume of amined, the interactive design procedure storm-water runoff, Q. Calculate the total can begin.

area(s) contributing flow to the ditch. (Use the rational method.) Using the appropriate

## Design Steps Formula, Find Q.

The steps used in design follow:
Step 2. Determine the slope, S, in feet per foot. If the slope is already known as a percentage, it may be converted to units of feet per foot by simply dividing by 100.

are determined in steps 6 and 3, respectively. If the calculated Q from step 7 is not more than 5 percent greater than the design Q, the ditch selected can be used. If the calculated Q is more than 5 percent greater than the design Q, reduce the velocity and repeat steps 4, 5, 6, and 7.

Step 3.

Select trial values for resistance, n, and velocity, V. From Table 6-6, page 6-44, select a value of the resistance or roughness coefficient, n, and a velocity, V, for the soil type in which the ditch is to be constructed.

If the calculated Q is smaller than the design Q by more than 5 percent, increase the velocity, However, do not make it any larger than the maximum for the soil or lining based on Table 6-6. If the calculated Q is still less than the 95-percent limit, the cross section must be increased by flattening the side slopes or by increasing the bottom width (if a trapezoidal section is used).

The initial trial velocity should be held to 1.

feet per second below the high value. Usually, the channel will be carrying less than design flow, reducing the velocity and making sedimentation likely. If a high value is chosen for the design velocity, this deposited material will be removed by the water during a peak flow without causing extensive damage to the channel.

Step 4. Determine the hydraulic radius. From the slope, S; Manning's n; and the velocity, V; find the hydraulic radius of the ditch, using the nomograph or equation.

Step 8. Provide freeboard. Add 0.5 foot to the water depth to provide freeboard.

Freeboard is the additional ditch depth over that required to carry the design flow. This added depth allows the ditch to carry the design capacity, even with sediment in the ditch bottom. The total depth, including freeboard, will be the cutting depth and the depth at which the ditch grade will be set.

Call this    to distinguish it from the R
values in Appendix C of this manual, which will be Example:
Step 5. Determine the type of ditch cross section.

Where Q is greater than 60 cubic feet per second, use a trapezoidal ditch. Where Q is equal to or less than 60 cubic feet per second, use a triangular ditch.

Whether the ditch is symmetrical or nonsymmetrical will depend on the specific location.

Design a ditch to carry a peak volume of storm-water runoff equaling 47,3 cfs from a culvert to a stream that is 289 feet from the outlet of the culvert. The ditch invert (or bottom) elevation at the outlet of the culvert will be 7.0 feet above sea level. The ditch invert will be constructed above the stream high watermark at an elevation of 5.5 feet above sea level. The ditch lining will be the bare (unturfed) GMd soil, as excavated.

Slope = invert at culvert or 7.0 ft - 5.5 ft distance from culvert to stream Step 6. Select the appropriate hydraulic radius and area table, From Appendix C, select the appropriate hydraulic radius and area table for the desired ditch cross section. Identify the column headed with the tentative side-slope ratios. Enter the table, locating the value of    that corresponds with Then find the cross-sectional area and ditch depth corresponding to    and    In using the tables, if the exact    value is not available, use the next smaller    value listed in that column.

6-37)
Soil (GMd): V = 3 to 5 fps (Table 6-6)
= 0.024 (Table 6-3, page Step 7. Calculate Q. Q = *AWV,* where area, Use the equation and velocity, V, Solution (Nomograph and Table Method):
The solution of a ditch problem is always a trial technique in which several values of velocity arc used.

Tables are recommended to tabulate the results. The tables should be similar to the ditch design work sheet shown in Table 6-7.

point. This turning point will remain (he same as long as neither S nor n changes.

The hydraulic radius, Rm, is found by connecting the velocity (in the second column from the right) and the turning point by drawing a straight line through to the R
scale. Then read the hydraulic radius (R)
in the second column from the left. This gives the required R for any given V in Manning's equation. In this example, R = 0.86. Enter this value on the work sheet.

The R value can be computed by using the calculator method shown in Figure 6-27, page 6-46.

Step 1.

Select a ditch.

Since design flow, Q, is less than 60 cubic feet per second, the ditch should be triangular. The channel is not a roadside ditch, so it should be symmetrical.

Select side slopes for a 3:1 triangular ditch for the first trial. (This assumes that periodic vehicular crossings are expected.) These factors can be changed if the ditch design is not suitable. Enter the information in the columns under ditch selection on the ditch design work sheet.

Step 4. Find the hydraulic radius,    in the ditch table. Locate the appropriate table among Tables C-2 through C-10 in Appendix C of this manual. There are four types of tables: V-triangular or symmetrical, V-triangular or nonsymmetrical, trapezoidal-symmetrical, and trapezoidalnonsymmetrical. For this example, use Table C-2 for a symmetrical V ditch.

Step 2. Select the velocity. The erosion velocity for the soil is 3 to 5 feet per second. This means that at 3 feet per second the soil in the ditch may begin to erode, and at 5 feet per second the whole ditch will be eroding. Since it is preferable not to exceed the     of 5 feet per second, the best initial choice is usually 1 feet per second lower than      or 4 feet per second.

Enter this figure on the design work sheet.

Locate the pair of columns representing the side slopes of the ditch being designed (for example, 3:1). Locate the    values that fall above and below, or the one that is exactly equal to, the    value found from the nomograph of Manning's equation. In this example, the
= 0.86 cannot be found in these columns, but the values 0.85 and
0.90 arc given, Use the lower value (0.85)
on the work sheet.

Step 5. Record the area and depth. With
 = 0.85, the corresponding area found in Table C-2 is 9.72 square feet, and the depth (d) found in the column at the far left is 1.8 feet, Record these values under the appropriate headings on the ditch design work sheet.

Step 3. Determine the hydraulic radius, from the nomograph. Using the nomograph (Figure 6-26, page 6-45), first locate a turning line.

The line is in the center on the nomograph. Find the turning point by locating the slope, S (in feet per foot), in the left column of the chart and the roughness coefficient, n, in the right column. Draw a straight line to connect the two points. The point at which the new line crosses the turning line is the turning Step 6. Check for Q. Check to see if this particular ditch will mcct the requirements of the design by performing the calcula -
tionscleaning and requires little maintenance.

Peak runoff will remove any silt buildup from the channel bottom. With V = 4.2 feet per second, there may be some erosion of the ditch, but it should not be a significant maintenance problem. The shape, lining, and slopes are acceptable.

Q = Q = (9.72 sq ft)(4.0 fps) Q = 38.9 cfs
Step 8. Determine the cutting depth. The water level in the ditch should be at least 0.5 foot below the edge of the ditch as a safety factor. Accordingly, the cutting depth is the water depth plus 0.5 foot of freeboard.

Cutting depth = d + freeboard
Using the rutting depth just calculated, This calculated quantity of flow (Q) must fall within 5 percent of the design flow of 47,3 cubic fect per second, or between 44.9
and 49.7 cubic feet per second.

If this requirement is not met, as in this case, try a new velocity.

If the calculated Q is less than 95 percent of the design flow, use a higher velocity. For this example, since
38.9 is less than 44.9 cubic feet per second (the lower limit of the acceptable range), a velocity of 4,5 feet per second would be an acceptable assumption for the next trial.

**Cutting depth = 1.9 + 0.5** = 2.4 ft
Since there are 2.5 feet (8.0 - 5.5 = 2.5) of available cutting depth at the end of the ditch, the design is acceptable. Conclusion: Use this ditch. Alterna Live Solution (Calculator Method):

Rm = 1.0 R t = 0.95 Aw = 12.0 sq ft. d = 2.0 ft Q = (4.5 fps)(12.0 sq ft) Q = 54.0 cfs, which exceeds 49.7 cfs, so the ncx[ trial velocity must be less than 4.5 fps: try 4.2 fps.

If it is more convenient to use the calculator method than the nomographmo the following procedure is used:

V = 4.2 = 0.92 = 0.90 = 10.83 sq ft, d = 1.9 ft = (4.2 fps)(10.83 sq ft) = 45.5 cfs
Step 1.

Select a ditch.

As before, the ditch is V- type and symmetrical. Assume side slopes of 3:1 have been selected for the trial cross section.

Step 2. Select the velocity. The assumed trial velocity should always be 1 feet per second less than the maximum erosion velocity of the soil. In this case, it will be 4
feet per second.

Q is greater than the lower limit of 44.9
and less Lhan the high limit of 49.7. This ditch is within the range and thus meets the ditch water depth and velocity requirements. Enter this value of 9 on the ditch design work sheet.

Step 3.

Determine the hydraulic radius, Rm.

where
Step 7. Determine if the ditch is appropriate. This process describes a symmetrical, triangular ditch in GMd soil, with a slope of 0.0052 feet per foot and 3:1 side slopes. It carries 45.5 cubic feet per second runoff with a water depth of 1.9 feet and a velocity of 4.2 feet per second.

V = 4 fps n = 0.024 S = 0.0052 ft/ft
Since the velocity in the ditch is greater than 3 fps, the ditch can be considered self-
Stcp 4.

Determine the area of water, and depth of water, d. As explained in Figure 6-28
= *1/2(xd + yd)d* for any triangular ditch.

For this problem, x = 3, y = 3

2 = l/2(3d + 3d)d = l/2(6d)d = 3d
Therefore, the hydraulic radius (Rm) is
For depth (d), the depth of water for the conditions assumed in step 3, is calculated.

Since Rm = 0.848 from step 3, and Rm is also equal to 0.474d, the depth of water (d)
can bc computed.

This allows     to be computed.

The wetted perimeter (wp), as explained in Figure 6-29, is
Step 5. Check for Q.

2+ d + (yd) 2+ d w p .  Cl+ C2 = ( x d )
Substituting values of x and y
The Q calculated for the ditch must be within  5 percent of the design Q of 47.3 cfs, or between 44.9 and 49.7. The calculated ditch Q is 38.4, which is less than the lower limit and is unacceptable. Since the calculated Q is below the lower limit, raise the velocity for the next trial calculation. For the second trial, the assumed velocity will be 4.5 feet per second.

Step 6. Make a second trial calculation.

will tend to be very wide and shallow. To determine runoff capacity (in cfs) in this type of channel, open channel hydraulics, as previously discussed, must be modified.

## Gutters

Gutters are shallow, paved drainage channels used in more permanent construction adjacent to paved or hard-surfaced areas.

They provide positive removal of runoff, protection for easily eroded soils adjacent to the pavement, and prevention of softening of turf shoulder areas commonly caused by a large volume of runoff from adjoining pavements.

Q is too high; try V = 4.2 fps.

Step 7.

Make a third trial calculation.

Q is acceptable, because it is between the limits.

A cross section of a typical runway gutter is shown in Figure 6-30, page 6-52. This gutter conforms to US Air Force safety requirements and design charts of that particular gutter.

Safety and operational requirements for fast landing speeds make it desirable to provide a continuous, longitudinal grade in the gutter. Close conformity to the runway gradient requires the use of sump inlets (drop inlets covered by gratings).

A sufficient number of inlets should be provided in the gutter to prevent the depth of flow from exceeding 3 inches.

## Median Channels

Step 8. Determine the ditch. With the Q
being acceptable, the ditch will have a water depth of 1.92 feet and side slopes of
3:1. Additional depth must be added to the water depth for freeboard. This additional depth can be selected depending upon the conditions external to the ditch but cannot be less than 0.5 foot. Therefore

## Cutting depth = water depth (d) + 0.5 = 1.92 + 0.5 = 2.42 ft or 2.4 ft
Channels will be placed down the center of medians, dual roads, runways, taxiways, and other similar structures. These than -
nels will be symmetrical but very wide and shallow. The input flow into such channels is from surfaced and unsurfaced areas adjacent to the channel. The flow can be determined by the rational method. Since the factors of slope (S), Manning's n, flow
(Q), and the general width are known, the depth can be determined by trial using the flow equation or nomograph for flow in open channels.

- previous low flow, The velocity of 4.2 feet per second is acceptable. Some erosion may be anticipated, but it will not be serious. In addition, because of the high velocity, the flow will clean out the sediment from

## Berms Special Channels

Some facilities will have special types channels where surface runoff will be cepted and removed. These channels of interwill be similar to open channels, except they The uncontrolled inflow from drainage areas adjacent to open channels has been a source of numerous erosion failures. Combating this problem requires special consideration during the design of the surface drainage system.

Local runoff inflow can Where excavated material is wasted, as in a levee or dike parallel to the channel, there must be frequent openings through the levee to permit inflow to the channel. A
suitable berm allows a minimal amount of excavated material to flow back into the channel. This prevents sloughing from the spoil bank into the channel.

be particularly detrimental. Because of normal irregularities in grading operations, runoff becomes concentrated and causes excessive erosion as it flows over the sides of the channel. Experience shows that constructing a berm (raised lip), Figure 6-31, prevents this problem. Place the berm, usually made of earth, at the top edge of the channel. This berm prevents inflow into the channel except at designated points where an inlet, properly protected against erosion, is provided.

Runoff, Q, from the area is determined by the rational method. This runoff is collected and conveyed by the channel formed

## 6-52 Drainage

by the berm. The factors of Q, n, S, and width are used to solve for depth by the trial method.

without erosion.

When the grade is not sufficient to permit quick water removal, the ditch may require an asphalt or concrete lining. Berms may be constructed on the downhill side of interceptor ditches, as shown in Figure 6-31, to prevent overflow and excessive erosion of the downhill slopes.

## Construction And Maintenance Of Channels

Ditch construction normally requires either a grader or a scraper. Sometimes, these two items arc used in combination. Depend ing on the location, other factors must be considered in designing and building ditches.

Abrupt changes in a ditch's normal flow pattern will induce turbulence and cause excessive erosion.

These conditions develop most frequently at channel transitions, junctions, and storm drain outlets. Accordingly, special attention must be given to these locations during design.

Interceptor ditches should be set on grades, thus allowing for quick removal of water tures such as roads, bridges, and culverts.

Velocity and turbulence may also endanger the channel itself. In addition, the eroded material may sometimes be deposited within the channel in areas where it will cause damage.

In these cases, channel maintenance and repair will be a constant concern.

Channel maintenance problems exist in all drainage systems. The basic design of the ditch must consider these maintenance problems before they arise. Therefore, designers must have a thorough understanding of the two basic ditch maintenance problems: sedimentation and erosion. Channel protection and ditch shape, when used together, control maintenance problems most effectively.

## Sediment Control

Erosion most commonly occurs when the velocity of flow exceeds the velocity at which the soil of the channel will erode.

Table 6-8 shows the maximum velocities.

Erosion can be prevented by lowering the velocity below the soil-erosion velocity. This can be accomplished by lining the natural channel material with a more erosion-resistant material or by reducing the side slopes.

Table 6-9 shows the recommended side slopes.

Erosion should be considered and accounted for in the design of channels.

Water flowing overland tends to carry sediment into any open channels. When the velocity in the channel is 3 fps or less, this sediment can be deposited in the channel. Since most storms are less intense than the design storm, the channel bottom may accumulate a large volume of loose sediment. When peak flow does occur, the velocity should be great enough to scour the channel bottom clean of loose sediment. If the sediment is not removed, it will compact and gradually reduce the depth of the ditch. At peak flow, the ditch may overflow and cause damage to adjacent structures before the channel is cleaned out; therefore, the channel should be kept clean through maintenance.

When designing channels, keep peak velocity flow above 3 fps. This keeps the channel self-cleaning. A higher velocity is preferred, but such velocity must not exceed the maximum velocity for the soil. (See Table 6-8.) When the soil type requires a maximum allowable velocity under 3 fps, sedimentation will be a maintenance problem.

One solution is to line the ditch with asphalt or concrete. This reduces the coefficient of friction, thus increasing the velocity. When sedimentation is expected and linings cannot be used, increase the allowable freeboard to eliminate overflow.

## Erosion Control

Water flowing through open channels is turbulent. This turbulence increases as the velocity increases. Together, velocity and turbulence erode and carry away the soil of the channel and endanger nearby struc-

## 6-54 Drainage

ditches. Details on riprap and gabions are given on pages 6-116 through 6-123.

## Pavement Decreasing The Hydraulic Radius

When the design and construction are done properly, paving the ditch with asphalt or concrete will prevent erosion. Because of the low n values of different types of pavement, velocity may increase too much, causing erosion where the pavement ends.

Special protection, such as a stilling basin or rock lining, may be required at this point to slow the velocity before allowing the flow to continue into the natural soil channel. Because of pavemen 1's low n values, it can be used effectively to increase flow velocities if they are too low, thus preventing deposition.

## Installing Check Dams

Reducing the hydraulic radius will decrease the velocity. This decrease in hydraulic radius can be accomplished by increasing the wetted perimeter, wp, in relation to the area, A (while the Q remains constant).

This can be done by widening the ditch, flattening the side slopes, or widening the bottom. This increases the wetted perimeter without materially increasing the area. The required changes in ditch design are determined by the trial approach, since the amount of runoff, Q, must be retained while reducing the velocity.

## Lining The Channel

Erosion can be controlled by lining the bottom and sides of the channel.

The water velocity in a channel can also be reduced by decreasing the slope. However, except for local variations, building ditches at slopes other than that of the surrounding ground is impractical, One method for decreasing the slope is to install check dams or weirs, as shown in Figure 6-32, page 6-56.

Check dams should be considered when the slope ranges between 2
and 8 percent.

Channels with slopes of 2
percent or less generally do not require extensive erosion controls. With slopes in excess of 8 percent, it is usually more economical to pave the ditch with asphalt or concrete than to build check dams.

## Grass Or Turf Design

Since natural linings take considerable time to grow or effort to place, they are seldom used in the TO.

Correct spacing between check dams can be determined by using the following formula:

## Riprap

where
S = spacing, in feet, between check dams
(This value should not be less than 50
feet.)
Riprap lining involves placing rocks or rubble in the bottom and on the sides of the ditch to prevent soil erosion. Rocks should be hand-placed in at least two layers and compacted individually. Riprap not only prevents erosion but decreases velocity in the channel because of its high n value.

Riprap also helps prevent erosion when making transitions from paved to soil ditches or from other high-velocity ditches to those in which lower velocity is required.

Gabions are another method of lining H = height from the channel bottom to the lower edge of the weir notch (This value should not be greater than 3 feet unless the dam is to be structurally designed.

To prevent unnecessary work, the practical lower limit for H is 1 foot.)
A = slope of the original ditch in percent

B = desired slope in percent (This value
should be set at 2 percent. This is the
maximum slope that will not require addi-
tional erosion control.)

Example:

Original slope = 5%

The spacing between check dams is 100
feet. To prevent erosion of the sides of the channel at the check dam, a weir notch is built in the center of the dam. The weir notch must be designed to carry the flow in the ditch. Weir-notch dimensions for various flow rates are given in Table 6-10.

Desired slope = 2%
H = 3 ft

## Maintenance

Find S.

Erosion is a common problem with check dams. It usually occurs when the weir Some protection usually takes the form of an extended horizontal or sloping apron. Scour can also be prevented by anchoring the sides and bottom into at least 2 feet of compacted material. Then place riprap along at least 4 feet of the downstream channel. These construction techniques will prevent scour and undercutting.

notch is too small or is clogged with debris so that water flows over the top of the dam.

Scour begins on the area exposed to the hydraulic jump. If allowed to continue long enough, the erosion will extend to the area around the dam, as seen in Figure 6-33. If this occurs, there will be more damage caused to adjacent structures than if the dam had never been installed.

## Section Iii. Culverts

tions. Accordingly, culvert types and construction procedures are discussed prior to considering culvert hydraulics and design features.

A culvert is an enclosed waterway used to pass waler through an embankment or fill. The flow in a culvert depends upon several factors, including the lining, slope, headwalls, wing walls, and downstream condi -

## Culvert Types And Designs Permanent Culverts

headwall supports the soil mass at the end of the culvert and helps to protect against erosion.

Permanent structures can be constructed from corrugated metal pipe (CMP), concrete multiplate pipe arch, vitrified clay (VC), polyvinyl chloride (PVC], or other material.

Corrugated-Metal-Pipe Culverts CMP joints must be lapped so that water flowing through the culvert passes over the joint rather than into it. Failure to properly overlap the pipes will tend to force the flowing water through the joints and into the fill. All joints must be sealed, preferably with caulk or bituminous material. If joints are not sealed, voids may be generated around culverts, causing collapse of the fill. To increase the velocity for a greater quantity of flow, line the culvert with asphalt.

Commercial CMP is available with asphalt linings.

## Assembling Nestable Cmp

Because it is commercially available in numerous shapes, lengths, and diameters, CMP is commonly used in military construction. For TO construction, CMP is made of an aluminum-and-steel alloy. It comes in nestable half sections that, when assembled, give 2-foot effective lengths. It is available in the diameters and gages listed in Table 6-11.

The minimum diameter recommended is 18 inches for lenghts up to
20 feet and 24 inches for all other lengths.

Small diameters may become clogged with debris and are difficult to maintain.

CMP has flange-type fittings which arc easily fastened together by nuts and bolts that come with the sections. Vise grips and a ratchet set make assembly faster and easier.

## Concrete-Pipe Culverts

Specific construction techniques are employed in placing CMP. A retaining wall called a headwall is placed at the upstream end of the culvert. Headwalls arc always used upstream; they arc desirable but not mandatory for the downstream end. The When available, precast concrete pipe should be used instead of CMP for culverts.

It has two advantages over CMP. First, it is stronger and requires less cover than CMP
to support the same load, Second, the interior surface of concrete pipe is smoother
(Manning's n = 0.013) than CMP (Manning's n = 0.024). Because of these advantages, concrete pipe of the same diameter and slope as CMP will carry a higher flow.

Concrete pipe is fabricated in circular and noncircular cross sections, It is available in many lengths and widths. Seal joints between the sections to prevent excessive leakage and subsequent weakening of the field to traffic. To lessen this effect, use the alignment techniques shown in Figure
6-37, page 6-62.

fill section Substantial headwalls are required at both ends to prevent separation at the joints. Start assembly downstream and work upstream, ensuring male ends point downstream.

## Concrete-Box Culverts

To maintain an existing drainage pattern, place the culvert directly in the streambed, as in view (A) of Figure 6-37. Even though this may be diagonal to the fill, if the hydraulics of the channel are not changed, the stream will not change its direction.

Consider concrete-box culverts where the full area of the waterway must be used.

One advantage is that the box can be designed to withstand external loads with little or no cover. Box culverts are especially adaptable to rock sites, since the bottom of the culvert can be placed directly on the rock.

Concrete-box design requires knowledge of construction techniques for reinforced concrete structures.

Box culverts can be precast, but construction in the TO will probably require that they be cast in place.

## Expedient Culverts

Prevent the stream from shifting its course at the culvert inlet or outlet. Sometimes the structure will cut across a stream meander as in view (B) of Figure 6-37
This leads to doubt as to where to lay the culvert in the streambed. In this case, it is best to cut a new channel 10 lead the stream away from the structure. The old streambed must be filled and dammed with erosion-resistant material at the junction of the old and new channels. The dam can be built of sandbags, logs, riprap, or other similar material.

Expedient field-type culverts are built of material available on-site such as logs, oil drums, and sandbags filled with a sand-cement mixture.

Some examples of culverts built of these materials appear in Figures
6-34, 6-35 and 6-36. Expedient culverts built and sized properly should serve until permanent structures can be built. For evaluating hydraulics, end areas equivalent
10 CMP can be used for similar slopes.

Provide a smooth transition into and out of the culvert. The structure may cut across a bend of the stream, as in view (C) of Figure 6-37, with a straight run of the stream through the structure. If the bend is close to the structure, it is preferable to recut the stream as shown, and lay the culvert in the new streambed. Care should be taken to fill in and dam the entrance to the old streambed and the junction of the two streambeds, as descibed above.

## Culvert Construction

Proper placement is one of the most important factors during culvert construction. It is a major contributor to survival of the culvert under adverse conditions. Some things to consider in placing culverts arc culvert alignment: slope; fill placement; compaction under, around, and over the culvert; culvert length; and protection against erosion.

Move the water past the project as quickly as possible. When the channel flows paral- - lel. to the structure, erosion will even tually occur. To prevent erosion, dig a new channel routing the flow through the culvert and away from the structure, as shown in view (D) of Figure 6-37. Again, be sure tO
fill and dam the old streambed at the junction point.

## Alignment

The relationship of the culvert to the streambed is of major importance. Improper location can cause the stream to seek an alternative path other than the culvert. This could quickly close a road or air-
The alignment of ditch relief culverts is shown in Figure 6-38, page 6-63. The amount of flow and the slope of the ditch determine the spacing between culvert inlets. On a road with a 5-percent grade, relief culverts should be spaced 500 feet

## 6-60 Drainage

apart. On an 8-percent grade, spacing Slope should be reduced to 300 feet.

Culverts normally should be installed with the invert of both the inlet and the outlet of the culvert at streambed or channel elevation. The invert is the lowest point in the

Z  The outlet of the culvert can be raised
to reduce the slope, as shown in view (B) of Figure 6-39.
For culverts to be self-cleaning, flow velocity should be at least 3 fps. To achieve this velocity, the culvert should not be set on less than a 0.5 percent grade, if practicable. To prevent excessive outlet velocity, the culvert grade should not exceed 2 percent.

internal cross section of an artificial channel or the bottom of the culvert. The normal grade of the culvert can be modified by two techniques, as shown in Figure 6-39.

In general, free-falling outlets and culverts with slopes of more than 2 percent will require outlet erosion protection. In mountainous country where there are excessive stream slopes or in fills across dry valleys, culverts may have to be set at grades other than the terrain or streambed slope. In the TO, it may be advisable to accept the erosion problem and install the culvert with a slope for an excess of 2 percent. This will help to prevent a blockage caused by debris passing through the pipe.

## Depth Of Fill

- Drop inlets can be used to lower the
inlet of the culvert, This will tend to
reduce the slope of the culvert. An example of a drop inlet is shown in view (A) of Figure 6-39 and a discussion
begins on page 6-89.
The distance measured from the culvert invert to the edge of the shoulder or top of the fill, as shown in Figure 6-40, page 6-
64, is the depth of fill. The depth of fill must be equal to or greater than the cover plus the pipe diameter. Otherwise, a smaller diameter culvert or a drop inlet must be used. For a road culvert made of CMP, the largest diameter allowable must equal two-thirds the minimum fill depth.

## Cover

The depth of compacted soil from the top of the culvert (crown) to the finished construction grade is called cover. The culvert and the surrounding compacted soil must have sufficient strength to carry the compacted
.

soil backfill (dead loads) and the wheel and impact loads (live loads) of the traffic. Live loads are more damaging than dead loads on culverts under shallow cover, and dead loads are more damaging than live loads on culverts under deep cover. Accordingly, both minimum protective cover and maximum permissible depths of backfill must be included in design considerations for culverts.

During construction, provide adequate additional cover to protect the culvert from damage in places where heavy construction equipment will be crossing frequently.

culvert weight type.

These charts are good for 5,000 pounds more than listed. (For example, the chart headed "60,000-lb Singlewheel" is good for single-wheel loads up to and including 65,000 pounds.)
Each chart is subdivided into columns headed by culvert pipe diameters, in inches, and rows based on the gage of the metal.

Use linear interpolation for the incremental diameters not listed. The body chart gives the cover required, in feet, for the diameter and gage of pipe concerned.

The minimum cover required to protect the culvert pipe against live loads will depend upon the type of load. For road culverts, the minimum cover is one-half the diameter of the culvert, or 12 inches, whichever is greater.

The cover over culverts used in airfields must be specifically designed for the heaviest aircraft using the facility. Table 6-12 lists characteristics of US aircraft.

Use this table to determine the landing-gear configuration, wheel loads, and culvert weight type. This will, in turn, allow you to select the proper fill requirements category in Table 6-13, page 6-66, or Table 6-14, page 6-67.

To use these tables, find the chart that applies to the particular aircraft wheel or gear load and landing-gear type. Then use Table
6-12 to find the appropriate culvert type.

When the proper chart is located, read down the left column of the table to determine the appropriate row for the gage concerned.

When the proper row has been found, read horizontally to the right and find the minimum cover, in feet, under the column headed with the pipe diameter in Tables 6-13 and 6-14 give the cover requirements for culverts under airfields. These tables are composed of a series of charts based on aircraft load and gear configurations. Each of these charts is headed by a

## 6-64 Drainage

question. Two examples of this tabulation
60,000-lb single-tandem12-gage pipe.

follow.

(Use 60,000-lb single-tandem assembly (assy), chart 13.)
C130E Hercules12-gage pipe; from Table
6-12, page 6-65, C130E requires culvert WT
type 13.

From chart:
Example 2: 60,000-lb single-wheel8-gage pipe. (Use chart 5 in Table 6-13,)
The maximum permissible depth of fill as shown in Figure 6-40, page 6-64. The
(cover) for CMP is given in Table 6-15 for bedding is formed and shaped to fit the botsteel and Table 6-16 for aluminum alloy.

tom of the culvert. In addition, the founda-
Reinforced concrete pipe made under standtion is cambered (curved slightly upward), ard specifications can be used in fill up to as shown in Figure 6-41 along the center-
50 feet.

line of the culvert to allow for settlement and to ensure tightness in the joints. At Bedding (Foundations)
no time should the invert elevation increase The minimum bedding depth for pipe culas the flow proceeds downstream.

verts is one-tenth the diameter of the pipe Culverts are constructed on firm, well-compacted foundations. The composition of the soil on the bottom of the stream should be determined.

Good granular material will be required to form a proper compacted and shaped bed.

If a stream bottom is composed of poor material, such as organic matter, muck, silt, or large material that could puncture the CMP, remove and replace the material. The depth of material to be removed will depend upon information from borings. When the bearing strength of the soil is completely inadequate and uneven settlement is expected provide cradle footings. These footings may require piling as shown in Figure 6-42, Footings used for timber culverts as shown in Figure 6-43, can also be adapted for various types of culverts and soils.

Culverts can be placed on properly prepared rock foundations, Trench the rock and backfill with firmly compacted soil for bedding the culvert, as shown in Figure
6-44.

## Backfill

Take care in backfilling around the culvert, since the backfill supports the culvert against soil pressure generated by surface loads as shown in Figure 6-39, page 6-63. The soil selected should be placed carefully in well-compacted layers kept at the same elevation on both sides of the culvert. Compaction is done in 6-inch layers if hand- or air-operated or if other mechanical tampers are used.

If logs, hand tamping, or other expedient methods are used, place the soil in 4-inch layers. Carry the compaction from the culvert bed material to 12 inches or one-half the diameter above the top of the culvert (whichever is greater).

## 6-70 Drainage Length

Culvert length is determined by the width of the embankment or soil mass through which the culvert carries water. Culverts that do not include a downstream headwall must be long enough 10 extend a minimum of 2 feet beyond the toe of the embankment to prevent erosion.

## Headwalls, Wing Walls, And Aprons

Hcadwalls and aprons arc constructed to guide water into the culvert, prevent or control erosion, reduce seepage, hold the soil in place, and support the ends of the culvert. Headwalls close to roads should not protrude above the shoulder grade. They should be at least 2 feet outside the shoulder so they do not present a traffic hazard. Use headwalls on the upstream end of all culverts. If possible, use a headwall on the downstream end as well. When concrete pipes arc used, headwalls are mandatory at both ends.

Headwalls, both upstream and downstream, should have wing walls or retaining walls set at an angle 10 the headwall, This will help support the fill and d irect the water flow to prevent erosion.

The upstream wing wall will guide the water into the culvert and assist in improving the culvert hydraulics. The downstream wing wall, combined with an apron, will help reduce the velocity of the stream, and thereby lessen erosion al the outlet Ideally, headwalls and wing walls should be reinforced concrete or mortared stone. Standard designs are in the TM 5-302
series manuals. They can, however, be made of expedient material such as lumber, logs, or sandbags.

These structures are shown in Figure 6-45. For speedy construction in the TO, sandbags filled with a soiland-cement mixture may provide the best headwall possible.

When headwalls arc not used on the downstream end, the culvert should project beyond the toe of the fill at least 2 feet.

Use riprap to protect the projecting area culvert riprap, as shown Figure 6-46, page
6-72.

## Erosion Control

between the outlet and the stable channel, the outlet structure will be completely undermined. Erosion of this type may be considerable, depending on the location of the stable channel section relative to the outlet in both the vertical and downstream directions.

View (A) of Figure 6-47 illustrates this condition.

Culverts discharging into open channels should have antiscour protection to prevent erosion. Two types of channel instability can develop downstream from culvert and storm-drain outlets. These conditions, known as gully scour and scour hole, are shown in Figure 6-46. Predict the type of scour for a given field situation by comparing the original or existing channel slope or drainage basin downstream of the outlet to what is required for stability.

A scour hole or localized erosion, as shown in view (B] of Figure 6-47, is to be expected if the downstream channel is stable. The severity of damage to be anticipated depends on existing conditions or those created at the outlet. In some instances, the extent of the scour hole may be insufficient to produce either instability of the embankment or structural damage to the out-
Gully scour is expected when channel flow exceeds that required for stability. It begins at a point downstream where the channel is stable and progresses upstream.

If sufficient differential in elevation exists

## 6-72 Drainage

Headwalls, wing walls, or channel linings can absorb the energy of flowing water and reduce its velocity to acceptable levels.

When wing walls are not provided, line the stream bank and bottom for some distance downstream with riprap or other material.

Ditch linings were described in greater detail earlier in this chapter.

## Culvert Design

The hydraulic load on a culvert is the amount of water that will flow to the ulvert inlet, either as direct surface or channel-stream flow. Surface flow is determined by the rational and channel-flow-equations methods discussed earlier.

## Hydraulics Of Culverts

Culvert quantity of flow (Q) is the amount of water the culvert will carry in a unit of time. This capacity is expressed in cfs.

For a particular culvert of known size (A), shape, and interior roughness (n), the discharge capacity is controlled by one or more of the following factors:
let. However, in many situations, flow conditions produce scour that erodes the embankment and causes structural damage to the apron, end wall, and culvert. This type of outlet erosion of the bottom of the ditch and of the side banks is shown in Figure
6-48.

Height of the water above the culvert

inlet.

Hydraulic gradient (S) of the culvert.

Length (L) of the culvert.

Erosion is best controlled by two methods:
velocity reduction and channel protection.

Reducing the slope of the culvert reduces the velocity. This solution, however, may require a larger pipe since it changes the capacity of the culvert.

Elevation of the tailwater at the culvert outlet.

The hydraulic gradient and head are illustrated in Figure 6-49.

The normal flow pattern for culverts, for which Table 6-17 is used, is shown by view
(A) of Figure 6-49, In this case, the water is at crown elevation al the inlet, and the outlet is free-flowing.

The type of inlet is not generally considered in military culvert design. However, it should be remembered that the discharge capacity of a culvert will be increased by a smooth, transition type of inlet with headwalls and wing walls. For construction in the TO, the culvert should have a design capacity sufficient to pass the peak runoff from the design storm.

## Hydraulic Gradient

The hydraulic gradient (S) of a culvert is one of the culvert discharge capacity controls. It can be satisfactorily estimated as the slope in ft/ft. The gradient is calculated by dividing the head (H) on a culvert by the culvert length (L): S = H/L. The head is the difference in elevation between the following:
An accumulation of water at the inlet of the culvert is called *ponding.* When pending occurs, the outlet will normally be free-flowing, but the water will be at some depth above the inlet. When this depth at the inlet is 1.2D or less (where D is the diameter of the culvert), use Table 6-17 to directly determine Q and V. When the water depth at the inlet invert is greater than 1.2D and the outlet is free-flowing, use a nomograph (Figure 6-50, page 6-76) to determine Q, and use the continuity equation Q = VA to determine the velocity.

- The two ends of a culvert, if both the
inlet and the outlet are not submerged.
When both the inlet and the outlet are completely submerged, use Figure 6-50 exclusively.

- The water surface directly above the
inlet and the top of the outlet, if the inlet is submerged and the outlet is not submerged.
- The water surface directly above the
inlet and the outlet, if both the inlet and
outlet arc submerged.

## Critical Slope

extent of the pond, the requirement of safety to the structure, and the time it will take to empty the pond. These factors are determined by the runoff rate, the pond volume, and the culvert-flow rate.

They are derived using the following steps: Step 1. Determine the rate of runoff (Q)
the culvert must drain or, in the case of pending, the inlet drain capacity, Qd.

Step 2. Determine the length of the culvert. Step 3.

Determine the head on the culvert.

For a given size, A, of the culvert and a given head, H, on the culvert, the discharge capacity of the culvert will increase as the hydraulic gradient increases, This continues until the hydraulic gradient becomes equal to or greater than the critical slope, Sc. As the hydraulic gradient is increased beyond the critical slope, culvert discharge remains constant. The area decreases because the pipe does not flow full, and the velocity of flow in the culvert increases because V = Q/A. The critical slope is the maximum discharge.

## Roughness

Step 4. Using Figure 6-49, page 6-74, determine the size and type of pipe or box culvert required to handle the quantity of flow, Q.

For the selection of the pipe roughness values (n values) for flow determination refer to the footnotes to Table 6-17, page 6-75.

## Box-Culvert Flow

Flow characteristics of box culverts may be different from those of pipe culverts, even those with the same slope, lining, and inlet and outlet conditions. Flow, Q, can be determined as previously noted, for the conditions of inlet and outlet water elevations.

To use this table, enter the nomograph
(Figure 6-50) at the intersection of the length for the type and size of culvert (for example, point A in the nomography).

Extend the line horizontally to the turning-point line (point B in the nomography), and extend the line to the culvert head, H, in feet (point C in the nomography). Find the discharge, Q, in cubic feet per second, for the pipe selected at the intersection with the discharge line.

2) for CMP or 0.0 17(V
Step 5. Compute the discharge velocity, V, in fps. Use the equation, *V = Q/A.* If the discharge velocity is greater than the maximum permissible velocity for the outfall or the height of the water, in feet, above the top of the culvert inlet is less than 0.022(V
Assuming that the water elevation of the inlet is at the top of the box and the outlet is free-flowing, the difference in inflow characteristics between pipe and box culverts of the same material and slope is negligible.

Box-culvert sizes can therefore be determined by computing the cross-sectional area required for a pipe and then desgning a box of the same material, slope and cross-sectional area.

2) for concrete pipe or boxes, either select pipes of larger diameter or decrease the slope of the culvert. Example (Submerged Inlet, Unsubmerged Outlet):
When the water elevation is above the top of the box inlet, usc the nomograph in Figure 6-50.

In this case, make trial solutions until there is correlation between the box size and pending depth.

## Design Of Culverts With Submerged Inlets

Determine the most economical pipe size and number of pipes required for a culvert across an airfield. The following are known conditions:
The outfall from the culvert is a natural drainage channel with dense turf in a GP soil.

Submerging of the culvert inlet results in pending at-the site.

The elevation of the pond surface, which will determine the depth of submergence, is a function of the

Z The design flow, Q, is 210 cfs. Z 42-inch and 48-inch concrete pipes are
available.
Solution:
(c) If the exit velocity is based on a design flow of 70 cfs, the pipe would be flowing only partially full and the exit velocity would be 9.2 fps. This velocity is greater than when the pipe flows full because the resistance to flow decreases until the pipe is flowing approximately 0.8 full.

Step 1. Q = 210 cfs (given).

Step 2. L = 180 feet (given). Step 3.

Determine head, H.

ft + 3.5 ft] H 42-in = 598.6 ft - (593.0 = 2. 1 ft ft + 4.0 ft)
(e) Since allowable outfall velocity is exceeded and    < 0.017      use three 48-
inch pipes as the most economical available size.

## Appendix H 48-in -- 598.6 ft - (593.0)

## Design Of Pipe Culverts With Unsubmerged Inlets

Step 4. Determine the size and number of pipes required to handle the flow, Q.

The factors to be applied to the design of these culverts arc determined as follows:
Step 1.

Determine the rate of runoff. Use the area the culvert must drain. This will be the required capacity,     of the culvert.

Step 2.

Determine culvert use. Will it be used for a road or for an airfield?

(a) On the cast-concrete-pipe portion of the nomograph, draw a horizontal line from the intersection of the 180-ft L line and the
42-in pipe line (point A) to the turning-point line (point B). From B, draw a line to an H of 2.1 ft (point C). The intersection of this line with the "Q" portion of the nomograph shows the maximum discharge of one 42-in pipe to be about 78 cfs. For 210 cfs, three would be required.

Step 3.

Calculate the critical dimensions from the cross sections.

See Figure 6-51.

Determine the length in place (LIP) and the fill critical
(b) Similarly, for the 48-in pipe, 180 ft length, and 1.6 ft H, proceed from D to E
to F and find that one 48-in pipe would have a capacity discharge of about 92 cfs.

Again, three would be required for 210 cfs.

Step 4. Determine the largest pipe for the fill. Begin from the cross section at the outside edge of the shoulder. Consider only pipes that are available and for which cover is adequate.

Step 5. Compute the discharge velocity, V, and check for excessive outlet velocity. Check smaller pipe.

(a) Since three pipes are used, assume each will carry one-third the total Q or 70
cfs, whichever is greater.

For roadway loadings, the maximum culvert diameter is equal to two-thirds of the minimum fill (FT from Figure 6-51, page
6-79). The cover required for culvert protection is equal to one-half the diameter of the culvert or 12 inches (whichever is greater).

(b) If the pipe flows full, the exit velocity is
For runways and taxiways sustaining aircraft wheel loads, refer to Table 6-12, page 6-65, for the wheel loads and Table

Z
(Fill 1) = roadway elevation at the outer edge (EL1 - the elevation at the toe of the slope (EL2),

(Slope horizontal distance on the Inlet side of the road) = Fill 1 x the "X" value (horizontal
component of the Inlet side slope ratio).
Z
(Fill 2) = roadway elevation at the outer edge of the road on the outlet side ( EL3) - the
elevatlon at the toe of the slope on the outlet end,

(Horizontal distance of the roadside slope on the outlet end) = Fill 2 x the "Y" value (horizontal
component of the outlet side slope ratio).
Z
S (Slope) = the difference between EL2 and EL4 divided by the sum of S1 + TW (top width across the
road) + S2.

(Fill 3) = fill amount from the existing ground on the inlet side to the culvert inlet.

(Fill Total) = Fill 1 + Fill 3.
Z
1.
LIP (Length In Place) = S1 + TW + S2 + 2
Z
(Fill Critical) = Fill total minus DP (diameter of the pipe).
- Culvert weight type = 9.
6-13, page 6-66, or Table 6-14, page 6-67, for the minimum cover required.

- Q to be handled by culvert = 32 cfs.
Z Soil type is bare SC; therefore, the maximum allowable outlet velocity = 3-4 fps.

Step 5. Determine the culvert capacity, and outlet velocity.

Use values based on culvert material and slope and Table 6-17, page 6-75.

- Pipe sizes available: 24-, 30-, 36-, and
42-inch CMP, 10 gage.
Step 6.

Determine the number of culvert pipes required. Divide the area runoff, Q, by the pipe capacity,    Round up to the next whole number.

Referring to Figure 6-52, note that the following information is required before design can be accomplished:

Z
Horizontal length of one culvert, L.

Step 7. Determine the order length (OL).

The OL is calculated by multiplying the number of pipes (NP) times the LIP times a waste factor of 1.15, (See step 3 for the LIP and step 6 for the NP.)
Slope of culvert pipe needed to determine the flow characteristics of various pipe diameters (see Table 6-17, page 6-
75) and     which is a portion of the critical fill depth,

Z
Critical fill depth,     in order to determine if the cover over the pipe meets
the requirements of Table 6-13.
Step 8. Determine the maximum permissible discharge velocity,       Use Table
6-6, page 6-44, to calculate      for the channel lining into which the culvert outlet will discharge.

Determine the correct pipe to be used. Apply the following criteria in your calculations:

## Solution:

Z
Step 1.

Determine the runoff rate. Given for this example, Q = 32 cfs.

Step 2.
Determine airfield culvert use.
Be sure the outlet velocity is equal to or less than the maximum velocity of the channel lining into which the culvert outlet will discharge, If outlet velocity exceeds the soils      the outlet must be protected against erosion.


Use the least number of culvert pipes
possible to carry the total flow and still
be consistent with the above criteria.
Step 3.

Calculate the critical dimensions.

Computations should be made in the following sequence (see Figures 6-52 and 6-53):
Example (Unsubmerged Inlet):

- Determine the difference in elevation between the edge of the runway and the
culvert upstream invert.
607.00 - 600.80 - 6.20 - 6.20 - 6.

Determine the most economical pipe size and the quantity of pipe required for a culvert located under a runway, with the general data cross section given below. The maximum using aircraft weight cIass for this example will be an SR-71C.

- Determine the horizontal distance between the culvert invert and the
shoulder edge.
No headwall will be constructed down-stream. The following are known conditions:

= F1 x X = 6.20 X 10 = 62 ft
- Aircraft SR-71C. (Refer to Tables 6-12
and 6-13, pages 6-65 and 6-66.)

## 6-80 Drainage


(Fill 1) = roadway elevation at the outer edge (EL1 - the elevation at the toe of the slope

(Slope horizontal distance on the Inlet side of the road) = Fill 1 x the "X" value (horizontal
component of the inlet side slope ratio).

(Fill 2) = roadway elevation at the outer edge of the road on the outlet side (EL3) - the
elevation at the toe of the slope on the outlet end.

(Horizontal distance of the roadside slope on the outlet end) = Fill 2 x the "Y" value (horizontal
component of the outlet side slope ratio).

S (Slope) = the difference between EL2 and EL4 divided by the sum of S, + TW (top width across the
road) + S2.
Z
(Fill 3) = fill amount from the existing ground on the inlet side to the culvert inlet

(Fill Total) = Fill 1 + Fill 3.

1.
LIP (Length In Place) = S1 + TW + S2 + 2

(Fill Critical) = Fill total minus DP (diameter of the pipe).
Z Determine the difference in elevation between the edge of the runway and the
culvert outlet and fill slope.
NOTE: These computations depict the cross section and Figure 6-53, page 6-81, summarizes the calculations.

From these calculations, it has been determined that

607.00 = 599.62 = 7.38 = fit
- Determine the horizontal distance between the edge of the runway and the intersection of the culvert and fill.
- The actual length of the culvert is
235.8 feet, rounded up to an even
value of 236 feet. A 2-foot projection
is added because there is to be no
downstream headwall.
This gives a
culvert length of 238 feet for a single
pipe.
7.38 X 10 = 73.8 ft
- The slope of the culvert is 0.005 foot
per foot or 0.5 percent.
- Determine the actual slope of the culvert.
- The depth of fill at the critical section
is 6.5 feet (rounded to the nearest
tenth of a foot).
S = E L2 - EL4 S 1 + T W + S2

S =
600.8 - 599.62
1.18
62 + 100 + 73.8
235.8

= 0.005 or 0.5%
Step 4. Determine the largest pipe for the fill. Prepare a table as shown in Table 6-18 and fill in all known values.

Start by entering the largest pipe available,     into the table. Subtract Dp from total fill, F-T, to get fill critical,        represents the actual cover over the pipe at the critical section. Compare    to cover required,

Z Determine the incremental elevation difference between the elevation of the upstream invert and the invert of the
culvert at the critical fill section.
0.005 ft/ft = 0.5 percent

62 X 0.005 = 0.31 ft
- Determine the depth of critical fill section.
6.2 + 0.31 = 6.51 ft (Lenglh of horizon tal projection of the culvert.)
The upstream invert elevation to downstream invert elevation is
To find    for aircraft, refer to Table 6-12, page 6-65, which indicate that an SR-71C
aircraft has a culvert weight type (WT) of 9.

The CMP available is 10 gage. With this information, refer to Table 6-13, page 6-66, and select chart 9, corresponding to culvert WT 9. The diameters and cover are given in chart 9 under the 10-gage line. Starting with the largest pipe available, 42-inch or
3.5 feet,    is 4.0 feet (interpolated between pipe diameters.) Enter this value in Table 6-18. The 42-inch pipe (3.5 feet) cannot be used because its actual cover is 3.01 feet against a required cover of 4.0 feet. Repeat the process using the next smaller pipe available, 36-inch pipe. It has a    of 3.51
feet and a    of 3.5 feet. This pipe will work.

$\rm LIP=S_{1}+TW+S_{2}+2$ It

$\rm LIP=62+100+73.8+2=237.8$ ft: (Round Up to 238 ft)
Step 5. Determine the culvert capacity.

Use Table 6-17, page 6-75, to find the capacity and velocity for the 36-inch pipe.

The slope of the culvert is 0.5 percent.

Entering the graph from the top (pipe dameter), move down the column until you intersect with the slope in the left-hand column.

This will slate the quantity of flow in the pipe. The velocity of flow is shown by following the respective shaded or unshaded areas down and to the left until it ends in the velocity column, 4 feet per second.

Step 7. The next step is determining the length of pipe to be ordered. The order length is calculated by multiplying NP
(Step 6) times LIP (step 3) times a waste factor (WF).

Since pieces of material will be damaged in manufacturing, handling, transporting, and assembling, an additional amount over the actual in-place length will be required.

This value has been determined to be 15 percent of the total length of pipe required. For this project, the pipe selected will be 36 inches in diameter with a length in place of 476 feet.

The length to order will be
The 36-inch pipe has a capacity of 27.5
cubic feel per second for the 0.5 percent slope. The velocity indicated is 4 feet per second.

NP x LIP x WF

2 x 476 x 1.15 = 1,094.8 ft
The pipe comes in 2-foot increments;
therefore, the value of 1,094.8 is rounded up to the next even value, or 1,096 feet of pipe.

Step 6. Determine the number of pipe required to carry the flow by dividing the total (Q) of 32 cubic feet per second (step 1)
by the pipe capacity, 27.5 cubic feet per second (step 5) and rounding up to the next whole pipe. For this example, the number of pipe required is 32/27.5 = 1.2
or two 36-inch diameter pipes.

## Ponding Areas

Ponding is the accumulation of runoff at the inlet of a drainage structure resulting from the inability of the system to discharge more of the runoff than the rated capacity of the structure.

fill, the amount of freeboard required to prevent overtopping of the road, the height of the headwall and wing wall, and the time allowed for the pond to empty. When pending is anticipated, the adjacent fill side slope should be made less steep to prevent the sloughing of saturated fill.


The pond must be drained before damaging infiltration of the subgrade can occur. The actual time during
which pending is allowable will depend
upon the type and condition of the soil in the pending area and the embankment. In general, this period will be no
more than four hours from the start of the storm.
Military drainage structures in the TO are designed to discharge the runoff based on the 2-year design storm which, by definition, is expected to be equaled or exceeded at least once in the design period. Thus, a storm more severe than the design storm may occur and generate excessive runoff, overloading the drainage structures.

In anticipation of this event, design the areas around the inlets of drainage structures to accommodate a certain amount of pending.

In designing pending areas, the following assumptions are made to simplify the calculations and to retain satisfactory accuracy:

Z A culvert discharges its design capacity
before runoff starts to accumulate at
the inlet and form a pond.
- An increase in the head because of
pending does not increase the discharge
capacity of the culvert.
In some cases, due to limitations in culvert cover and space, terrain conditions, time, materials, or other conditions, a system may not be able to take care of the runoff from the design storm. To provide for this, include sufficient pending areas in the original plan to prevent flooding of vital areas. The pending areas store excess runoff until the intensity of the storm decreases and the structure can handle the flow.

The determination of permissible volume, the preparation of runoff curves, and the soil analysis must be done before designing pending areas to meet the above specifications and assumptions.

## Permissible Volume

When possible, military drainage systems arc designed to pass the runoff from the design storm without pending. However, some provision for pending may be made in those areas where flooding for a period of time will not affect the facility's operational status.

The following specifications are generally adhered to in the design of pending areas for military installations:

- The edge of the pond must be at least
75 feet from the edge of the pavement when used for runway and taxiway design.
The volume of permissible pending is determined by the elevations of the area available for such pending and the surrounding areas.

A contour map showing the final grading plan is required to compute the volume of permissible pending.

By inspection, a contour line may be selected to provide a pending area located a safe distance or elevation from the pavement. Pending volumes may be computed from the con tour map by the average-end-area method. This method is

- When a pond is used with road fills or
embankments, the depth of the pond will be determined by the porosity of the
the average of the areas, in square feet, enclosed by two adjacent contour lines and multiplied by the contour interval in feet.

feet. The 64-foot contour line encloses
10,000 square feet.

It should be noted that the contours are concentric: the 66-foot contour -line area includes the area bounded by the 64-foot contour line.

where
in cubic feet the first contour in square the next contour in square

V = volume A = area of feet B = area of feet b = vertical
The total volume of the pending area is
distance, in feet, between contours (contour interval)
10,000 + 35,000 = 45,000 cubic feet A further example of the computation of pending volumes by the average-end-area method is shown in Figure 6-55, page 6-86.

Assume that the pending area extends to the 68-foot contour line. Determine the volume of the pond. The 68-foot line encloses a total area of 30,000 square feet.

As an example of computing the volume for pending, consider the contours shown in Figure 6-54. Water can be safely ponded to the 66-foot contour line. The bottom of the inlet end of the culvert is at an elevation of 62 feet. Use a planimeter, or any other method, to determine the total area enclosed by each contour. In this case, the
66-foot contour line encloses 25,000 square Volume 62-64
= 10,000 cubic feet Prepare a cumulative runoff curve based on Volume 64-66
= 35,000 cubic feet to the-data given.

Pending may be required reduce the culvert size.

**Volume 66-68 = 2 x 30,000 + 25,000**
Tabulation of DataRational Method

= 55,000 cubic feet
All data required to plot a cumulative runoff curve, using the rational method, is shown in Table 6-19. Each column is prepared as follows:
The total volume available for pending will be 10,000 + 35,000 + 55,000 = 100,000
cubic feet, if the pending area extends to the 68-foot contour line.

## Runoff Curves

Column 1 is a tabulation of time in minutes.

Any similar combination of time increments can be used as long as enough properly spaced points are obtained to plot a smooth curve. The cumulative runoff curve is constructed by plotting time, in minutes (column 1), against volume in cubic feet (column 6).

TO determine the amount of water an area will contribute to a pond, a cumulative runoff curve must be plotted. The following example shows how such a curve is prepared:

## Example:

Column 2 is the product of the runoff coefficient, C (as determined for the area using the rational method), and the area in acres.

An area has 33.3 acres, consisting of 23.3
acres of impervious soil and 10 acres of paved surface. The weighted C value is
0.75, the TOC is 13 minutes, and the location intensity is 2.2 inches per hour for a
1-hour storm with a 2-year frequency.

Column 3 is the intensity, in inches per hour, for each one of the minute values of column 1.

These values are obtained from the standard intensity-duration curve number 2.2 in Figure 6-4, page 6-9. The value of 2.2 is the location intensity, in inches per hour, of the 1- hour, 2-year storm as specified in the given conditions.

Column 4 is the rate of runoff, Q, in cfs, for the entire interval of time shown in column 1.

It is obtained by multiplying columns 2 and 3 (Q = CIA). Column 5 is the time, in seconds, given in column 1.

Column 6 is the quantity of water supplied to the pond for the time given in column 1. For the first five minutes of rainfall, the quantity of water entering the pond is given by
Column 6 = (column 4)(column 5) Column 6 = (163)(300) = 48,900 cubic feet After 20 minutes from the start of rainfall, the volume of water would be equal to
105 x 1,200 or 126,000 cubic feet, if no water was released from the pond.

Q = 0.75 x 4.9 x 33.3 = 122.4 cfs. The number of culverts at a slope of 1.2 percent (Figure 6-55) when Q = 122.4 would be as follows:

## Preparation Of Cumulative Runoff Curve

30-inch pipe at 24 cfs = 6 pipes
36-inch pipe at 38 cfs = 4 pipes 42-inch pipe at 57 cfs = 3 pipes 48-inch pipe at 80 cfs = 2 pipes
60-inch pipe at 140 cfs = 1 pipes

These pipes in the above sizes and quantities will pass the flow without pending.

The cumulative runoff curve is obtained by plotting the volume (column 6, Table 6-19)
obtained by the rational method, on the ver -
tical axis and the time, in minutes (column
1, Table 6-19), on the horizontal axis. The cumulative runoff curve for the data listed in Table 6-19 is shown in Figure 6-56, page 6-88.

## Analysis For Ponding Analysis Of Cumulative Runoff Curve

Based upon the data given in the problem, the flow for the culvert design shown in Figure 6-55 would be determined as follows:

Q = CIA
The safe volume for pending is 100,000
cubic feet. The requirement is to reduce the flow past the outlet point by using a single culvert and allowing pending at the inlet.

where
C = 0.75
I = 4.9 for a TOC of 13 minutes and a location intensity of 2,2 inches per hour for the 1-hour, 2-year storm A = 33.3 acres Table 6-17, page 6-75, reveals that a
30-inch CMP culvert (n = 0.024) on a
1.2-percent slope discharges 24 cfs. Assuming that the pipe always discharges at the rated capacity, the cumulative discharge is a straight-line function for any time interval with a line passing through the origin.

Continue these straight lines so that they intersect thew cumulative runoff curve. At the point of intersection. the cumulative funff will have equaled the cumulative amount of water passed by the culvert.

From then on, there will be no pending.

storm. At the end of 42 minutes, the 30-inch culvert has theoretically been able to discharge 60,000 cubic feet. Therefore, the difference between the quantity supplied (175,000 cubic feet) and the quantity discharged (60,000 cubic feet) is 115,000 cubic feet, which must still be in the pond.

In view of the fact that the safe pending volume is only 100,000 cubic feet, 30-inch CMP is unsatisfactory because the safe pending volume would be exceeded.

Knowing how long the pond will exist behind the inlet, next determine whether or not the pending area is large enough. Figure 6-56 shows that the greatest vertical distance betweem the cumulative runoff curve and the 30-inch cumulative discharge volume is line P. Line P represents the maximum volume of water ponded behind the 30-inch culvert.

Make the same calculations for 36-inch culvert. In this case, the pond volume will be
75,000 cubic feet with a pond time of 95 minutes. Since the safe pending volume of
100,000 cubic feet and the 4-hour limit on the pending time arc not exceeded the
36-inch culvert is satisfactory. In addition, the excess volume of 25,000 cubic feet will be available for storms that may exceed the design storm.

Measuring line P by the vertical scale used in Figure 6-56 indicates that the maximum pending volu une will be 115,000 cubic feet.

a 42 minutes the cumulative supply curve shows that 175,000 cubic feet of water have been supplied to the pond by the rain-

## 6-88 Drainage Advantages Of Ponding

Although pending is an added safeguard against the effects of storms more severe than the design storm, its primary use is as an economy measure.

Pending allows for reductions in the size of culvert pipe necessary to handle runoff. However, if additional pipe or other construction is required for pending, check the additional cost against the savings in reduction of pipe size. Ponding appreciably reduces pipe sizes for areas that have a short TOC. For longer TOCs, pending has little or no effect on pipe sizes.

The use of pending as an economy measure is often restricted by the area available for pending.

This area should be sufficient to satisfy the requirements of the design storm, It should also have enough reserve capacity to take care of storms more intense than the design storm, Facilities for pending should be coupled with initial grading operations, if possible, to secure the most efficient use of personnel and equipment.

## Drop Inlets And Gratings

range from the weight of debris collected over the grating to vehicle or aircraft wheel loads.

Inlet grating should be placed 0.2 foot below the grade.

This will allow for the settlement of the area around the grating and will provide a sumped area to ensure complete drainage around the grating and positive interception of surface and gutter runoff.

Drop inlets, vertical entrances to a culvert or a storm drain, may be used to lower the elevation of the culvert inlet below ditch elevation. This is done where fill does not provide sufficient cover or where discharge velocity is erosive and can be controlled only by changing the slope. For storm drains (underground culverts or conduits designed to carry surface runoff), drop inlets are used to collect surface runoff from paved and turfed areas, street gutters, and ditches.

A typical drop inlet is shown in Figure 6-57, page 6-90.

To determine the proper size of grating-
Q,
1. Determine the peak rate of runoff, from the area that drains into the drop inlet. This will be the required discharge capacity, Q, of the grating.

A framework of bars, or a perforated plate called a grating] passes the storm runoff into a drop inlet. The grating serves as both a filter and a cover for the inlet. Gratings arc shown in Figure 6-58, page 6-91.

## Construction Of Drop Inlets And Gratings

2. Determine the load (depth of water or head) on the grating at times of peak runoff. When a drop inlet is used in a ditch, gutter, or pending area, the head will be the depth of water running in the ditch or gutter, or the depth of the pond.

3. Knowing the head, H, and the design discharge capacity, Q, refer to Table 6-20, page 6-91, to select the minimum size grating required.

Drop inlets should always be protected with some type of grating. An expedient grating can easily be fabricated using reinforcement bars welded together. These gratings should be spaced to readily admit debris which will pass unobstructed through the culvert. A drop inlet may be constructed of concrete, brick, timber, or CMP sections.

4. Multiply the required grating size by the appropriate safety factor to determine the actual grating size to use.

Inlet grating should be fabricated of steel bars, steel plate, cast iron, or reinforced concrete with adequate strength to withstand the anticipated load. The loads may A safety factor of 50 percent (1.5 x total grating area) for paved areas and 100 percent (2 x total grating area) for turfed areas should be added to the grating-area measurement to compensate for debris caught in the openings. Grating openings should be at least 18 inches long and should be placed parallel to the direction of flow.

The area of the grating openings is estimated at 50 percent of the total grating area. When using bars with large openings, determine the area of grating openings.

## Maintenance Of Drop Inlets And Gratings

Drop inlets and gratings require continuous maintenance because debris collects at the openings.

A maintenance schedule must be established to check and clean debris from the inlets and gratings. If these openings are not kept clean, a pond could form at the inlet, resulting in damage to nearby structures.

This damage could consist of saturation of the subgrade by the pond or direct flooding of adjacent areas. Periodic maintenance of drop inlels should include removing the cover and inspecting and cleaning the chamber.

Expedient drop inlets of the type shown in Figure 6-39, view (A), page 6-63, must be covered with bars, If the box is left open, it will tend to fill with debris making cleaning difficult, especially if a pond has developed.

## Subsurface Drainage Subsurface Drainage Criteria

a typical example of a subgrade drainage section.

Figure 6-61, page 6-96, will serve as a guide for spacing drains. These drains, although similar to base drains, have a larger area of filter material in contact with the subgrade.

When surface failures prove that natural subsurface drainage is inadequate, it becomes necessary to determine if a subsurface drainage system is needed, and if so, what type to install. Generally, subsurface drainage may be divided into three classes: base drainage subgrade drainage, and intercepting drainage. Base drainage generally consists of subsurface drainpipes laid parallel and adjacent to pavement edges with pervious material joining the base and the drain. Figure 6-59
shows a typical section of base drainage.

Intercepting drainage is required when water seeping into a pervious layer will raise the groundwater locally to a depth of less than 1 foot below the bottom of the base course. This condition is often encountered in thin, pervious soil layers; in exposed rock cuts; or in seepage from springs. A typical intercepting drainage section is shown in Figure 6-62, page 6-97.

## Subsurface Drainage Techniques

Subsurface water can be controlled through a combination of techniques. The techniques and combinations depend on the conditions existing in the area to be drained.

The techniques that follow should be considered when planning and designing subsurface drainage.

Base drainage is required where frost action occurs in the subgrade beneath the pavement and where ground water rises to the bottom of the base course through natural conditions or from ponding of surface runoff. Where pavement becomes temperarily inundated and there is little possibility that the water will drain from the base into the subgrade base drainage will be required. Table 6-21, page 6-94, establishes the criteria to follow in these cases.

## Depth Of Base Course

Base drainage is also required at the low point of longitudinal grades in excess of 2
percent where the subgrade coefficient of permeability is less than 1 x 10
The base course may be built up to a specified depth above the groundwater table.

Generally, the finished grade must be at least 5 feet above the mean groundwater table level. This technique is feasible when

Z A gravity drainage system is impractical. Z The condition to be controlled is limited
to a small area such as a narrow swamp
crossing.
- Adequate base-course material is available.
-3 fpm. The coefficient of permeability, a property of each soil type, is defined as the discharge velocity at a unit hydraulic gradient. Determine the coefficient of permeability experimentally, either by laboratory test or by an actual field test of the soil involved. The coefficient is expressed in units of velocity such as fpm or centimeters per second (cm/see). Base drainage is required if the subgrade coefficient of permeability is smaller than the coefficient of permeability indicated in Table 6-22, page 6-94.

## Deep Ditch

Where ditches will not interfere with operations or become a hazard to traffic, deep V- ditches with free outfall may be feasible. Easily built and readily enlarged, these ditches provide positive interception and Subgrade drainage is required for permanent construction when seasonal fluctuations of groundwaler may be expected to rise to less than 1 foot below the bottom of the course.

Figure 6-60, page 6-95, shows

## 6-92 Drainage Natural Drainage Channels

drainage of subsurface water before it reaches the area to be protected. Erosion, maintenance, traffic, and right-of-way are factors to be considered before using this solution, Where possible and practical, water in existing natural drainage channels should be lowered when corresponding effective lowering of the groundwater table will occur.

This technique may be particularly effective in pervious soil.

## Subsurface Pipe

In cases where a V-type or other open-ditch type drainage system is not practical, it may be necessary to resort to construction of subsurface drainage. Failure of the subsurface system stemming from improper control of the grade, the bedding, the pipe placement, the placement of filter material, or other installation work gives no warning prior to failure.

Such failure is extremely difficult to repair when discovered.

## Blind Drains

The most common form of subsurface drainage is perforated pipe. Where the perforations do not extend completely around the circumference of the pipe, the pipe is generally laid with the holes down and the joints closed. Materials used in manufacturing this type of pipe arc corrugated metal, cast iron, vitrified clay, nonreinforced concrete, bituminized fiber, and asbestos cement.

these drains are for perforated or materials used Blind or *French* drains are constructed by filling a ditch or trench with broken or crushed rock.

The top surface of the rock may be left exposed so that the trench will act as a combination surface and subsurface drain, or the rock may be covered by a relatively impervious soil so that no surface water can penetrate. The latter is the general practice.

In general, French drains are not recommended for permanent construction because they tend to silt up over time, In TO construction, often used as a substitute open-joint pipe or on filter with such piping.

Bell and spigot pipes can be laid with open join ts. If the filter material has been properly designed, collars are not needed over the joints. This type of pipe is generally made of vitrified clay, nonreinforced concrete, or cast iron.

Materials commonly used in manufacturing farm tile are clay or concrete.

## Combination Drainage System

Porous concrete pipe is laid with closed joints. It collects water by seepage through the wall of the pipe and should not be used where sulfated waters may cause disintegration of the concrete.

Farm tile is laid with butt joints slightly separated to permit collection of water through the joint.

Because of its low resistance to high-impact loads, farm tile is not recommended for use on airfields.

Combination drains, which attempt to handle both surface runoff and subsurface water in the same pipe system, are recommended.

Surface runoff often carries sediment and soil from the drained area into the system.

This clogs the system and causes flow stoppage. For this reason, subsurface drainage systems using some form of piping are generally sealed so that surface runoff can-
PIPE-LAYING CRITERIA
not enter. The only drainage system which will satisfactorily handle both surface There are essentially four different types of runoff and subsurface water is the open pipe available for subsurface drainage, as channel or ditch.

previously mentioned. They should be laid according to the following specifications:

Z Manholes should be provided at intervals of not more than 1,000 feet, with
flushing risers between manholes and
at dead ends as shown in Figure 6-60,
page 6-95.
- The minimum slope for subdrainage
pipe is a 0.15-foot drop in elevation per
100 feet of length, The elevation of a
pipe at any particular location is generally specified by the invert elevation, in which the invert is defined as the lowest
point in the internal cross section of the
pipe at the particular location.
- Pipe should be at least 6 inches in diameter with 6-inch pipe being used for
all drains. With long intercepting lines
calcium chloride or a layer of hay to prevent freezing.

or extremely severe groundwater conditions, 8-inch or larger pipe may be necessary.

A layer of filter material approximately 6
inches deep should be placed around all subsurface piping systems. The selection of the proper filter material is very important since it determines, to a great extent, the success or failure of the drainage system.

The improper selection of filter material can cause the drainage system to become inoperative in one of three ways:

Z The center of subgrade drains should be
located at least 1 foot below the bottom of the base course and not less than 1
foot below the groundwater table. Normally, subgrade drains are required
only at the edges of pavement areas where the soil is pervious and drains well. However, local groundwater conditions and base and subgrade soil characteristics may require closer spacing of
the drains, When the drain discharges
into a culvert or any considerably larger
pipe, it should discharge above the
water level in the larger pipe. When the drain discharges into a pipe of equal or
only slightly larger size, it is generally
better 10 bring the drain in above the
receiving drain and make a vertical connection between the two. This will pre -
vent the water from backing up in the drainage pipe since these pipes rarely
flow full
Criteria have been developed, based upon the mechanical-analysis soil curve, to prevent the above failures.

to
Z When the impervious layer is at a
reasonable depth, intercepting drains
should bwe placed in the impervious layer below the intercepted seepage
stratum. The quantity of water collected by an intercepting drain is difficult to determine, but in general, 6-
inch pipe is sufficient for lengths up
1,000 feet.

## Vertical Wells

to
A great deal can be learned about gradation characteristics of a particular soil by observing the soil curves on the mechanical analysis chart. Well-graded soils generally have a smooth, grain-size curve with gradual changes of slope. Poorly-graded, uniform soils generally have a very steep grainsize curve.

Skip-graded soils have a grainsize curve with a characteristic hump in it.

The filter material in skip-graded soil tends to segregate during placement. The grainsize curves in Figure 6-63 show various gradation characteristics.

Vertical wells arc sometimes constructed allow trapped subsurface water to pass through an impervious soil or rock layer A coefficient of uniformity,     value of less than 20 is desirable to prevent segregation of coarse and fine-grain particles, especially during placement.

For the same reason, skip-graded material should not be used. Placing the filter material while it is wet can reduce segregation.

to a lower, freely draining soil layer. If drainage is obstructed, additional wells are built or the pocket is drained with an easily maintained lateral subdrain system. Vertical wells S are often used in northern latitudes where deep freezing is common.

They permit fast runoff from melting snow to get through the frozen soil and reach a pervious stratum.

Under such conditions, the bottoms of these wells are treated with Filter material can clog a pipe by moving through the perforations or openings.

## Filter Material

- The pipe may become clogged through
infiltration of small soil particles.
- Particles in the protected soil may move
into or through the filters, causing instability of the surface.
- Free groundwater may not be able to
reach the pipe.
Prevent this by using the following specifications:
For a slotted opening
To permit free water to reach the pipe, the filter material must be many times more pervious than the protected soil. This condition is fulfilled when
For a circular hole
Use the following methods to prevent particles from the protected soil from moving into or through the filter or filters:
If it is not possible to secure a mechanical analysis of available filter materials and protected soil, concrete sand with mechanical-analysis limits as shown in Figure 6-63
may be used.

Experience has indicated that a well-graded concrete sand is satisfactory as a filter material in most sandy, silty soils.

## Steps In Filter Design

Select that filter material which best meets the above criteria.

Obtain a mechanical analysis of each sandy soil from several readily available sources.

Obtain a mechanical analysis of the subgrade soil (protected soil) at the bottom of the trench which will be in contact with the filter material.

Install pipe to grade, bedded and surrounded with the selected filter material as shown in Figure 6-58, 6-59, or 6-60, pages
6-91, 6-93, and 6-95, respectively.

Plot the mechanical analysis of each soil on semilogarithm paper and draw a curve for each soil.

## Selecting Filter Materials

From the mechanical-analysis curve for each soil, determine the diameter, in millimeters (mm), of the particle of each sample. Ten percent of these particles are finer (by weight)      The subscript "10" indicates the percentage, by weight, of the soil sample which is finer (smaller in diameter) than the particle in  size Similarly, determine the         and
      particle size for each soil.

Determine the slot width or hole diameter, in millimeters, of the type of pipe to be used. Check the coefficient of uniformity, CU, to ensure
Filter material should be selected with a view toward the simplest construction and the lowest cost. To further this end, try to use only one layer.

If several layers of filter material are required, one layer should be confined to the region around the pipe openings and another layer placed between it and the protected soil, as shown in Figure
6-59, page 6-93.

In this case, the designer selects a filter material for use around the pipe according to the filter design formulas.

The second filter material is then designed to protect both the inner filter material and the surrounding soils. In other words, the design of a multilayer filter for a subdrain system should proceed outward from the inside filter material to the subgrade soil being protected. Example (Selecting Filter Material):
Check the design criteria for clogging of pipe openings to ensure

(1)
(2)
A suitable filter material must be selected for a 6-inch pipe with 1/4-inch diameter perforations to protect a subgrade soil with an E curve (shown in Figure 6-63, page
6-99). The soils represented by curves A
and B are readily available from local borrow pits. Tabulate data from the mechanical-analysis curves.

Check the design criteria for movement of particles from the protected soil (subgrade) through the filter material to ensure
(1)
(2)
Check the design criteria for relative perviousness to ensure
Check the coefficient of uniformity of both soils.

Soil A

Should be         5 to permit water movement through the filter.

0.30 0.01 = 30 which is > 5. Soil B
Should be > 1.0
to prevent clogging of the pipe.

Thus, both soils A and B satisfy the require ment that the coefficient of uniformity be less than 20.

Apply design criteria to soil A, of Note that the soil particle size is usually given in millimeters, while the hole size is usually given in inches. The two dimensions must be expressed in compatible units before the preceding formula is used.

To make this conversion, multiply the size of the pipe perforations, in inches, by 25.4 which represents the number of millimeters per inch. For example, with soil B under discussion
Should be       5 to prevent movement subgrade soils through the filter.

24.4 which is not $\leq 5$.

Soil A is unsuitable because movement of which is > 1.0.

the subgrade soil through the filter material is possible.

Thus, soil B satisfies all the criteria for a good filter material while soil A dots not.

Apply design criteria to soil B.

(filter)
(protected soil)

## Installation Of A Subdrainage System

Should be      5 to prevent movement of subgrade soils through the filter.

which is < 5.

(filter)
Should be      25 to
(protected soil)
prevent  movement of subgrade soils through the filter.

= 2 3 . 8 which is < 25. 1.0 0042
The most efficient and most practical type of subdrainage system is one which adequately performs the operations for which it was intended and, in addition, was installed with the care and skill consistent with its purpose. Any attempt to lower the quality of construction or to usc a sketchy or inadequate subdrainage system can result in disastrous failures. Conversely, any attempt to install an elaborate system of underground piping where a simple V ditch would serve as well is inadvisable.

## Section Iv. Surface Drainage Design In Arctic And Subarctic Regions Applicability

subarctic coincides with the circumpolar belt of dominant coniferous forests.

## Hydraulic Criteria For Cold Climates Rainfall

This section discusses the problems involved in the design of drainage facilities in arctic and subarctic regions. While the design data presen ted has been developed primarily for Alaska, the methods used are generally applicable to other arctic and subarctic regions. Arctic in Arctic is defined as the northern region which the mean temperature for the warmest month is 50o Fahrenheit (F) or less, and the mean annual temperature i s below 32o F. In general, the arctic coincides with the tundra region north of the limits of trees.

## Subarctic

A study of rainfall intensity-frequency data recorded at arctic stations indicates a considerable variance between the average intensity of rainfall for a period of one hour and the average precipitation rates of comparable frequency for a duration of less than one hour. This is evidenced when compared with similar rainfall in the continental United States (CONUS). Even within the area of Alaska, there was a noticeable difference between the rains at Juneau and those at Fairbanks. The higher values for rainfall intensity were used to develop design intensity-duration (supply) curves, which are shown in Figure 6-64, For design purposes, a minimum rainfall rate of 0.2 in/hr is recommended, even where maps of intensity-frequency Subarctic is defined as the region adjacent to the arctic where the mean temperature is
32 F or below for the coldest month and 50 F or above for the warmest month, and where less than four months have a mean temperature above 50o F. In general, the other areas, a good guide may be obtained when test borings are made, Values normally would not exceed about 0.5 inch per hour for coarse sands and gravels and would be as low as 0.1 inch per hour for clayey soils with low permeability.

## Storm-Drain Design

Design-storm index.

One-hour rainfall intensities having various average frequencies of occurrence in the arctic and subarctic regions of Alaska are shown on maps in Figure 6-65, page 6-104. This figure, on which rainfall depth curves are superimposed, is known as a design-storm index.

The curves are labeled by the one-hour amounts of rainfall that are represented;
these, in turn, are coordinated with the intensity-duration or supply curves of Figure 6-12, page 6-17, Figures 6-64 and 6-65, used in combination, provide a means whereby rainfall intensities sufficien tly accurate for runoff computations for any duration may readily be determined.

The type and capacity of storm-drain facilities required are determined primarily by the promptness with which design-storm runoff must be removed in order to avoid serious interruption or hazard in the use of important operational areas as well as prevent serious damage to pavement subgrades. It is presumed that all phases of site reconnaissance have been carefully completed and that information is available which shows topography, natural drainage patterns, groundwater conditions, and seasonal frost and permafrost levels.

## Basic Considerations

Even though rainfall magnitudes are small in arctic and subarctic regions, drainage is an important factor in selecting an airfield site and planning the construction. The planner should be aware of several features related to drainage in order to ensure a successful design. These features include the following:

- Sites should be selected in areas where
cuts or the placement of base-course
fills will not intercept or block obvious
existing natural drainage ways,
- Areas with fine-textured, frost-susceptible soils should be avoided, if possible, In arctic and subarctic regions, most soils are of single-grain structure with a
very small percentage of clay. As a consequence, cohesive forces between grain
particles are very small and the material
erodes easily. Frozen, fine-textured soil
profiles may also contain large amounts
of ice lenses and wedges.
Elevaton and physiographic orientation.

Present information is insufficient to establish quantitative conclusions of the effects of elevation and physiographic orientation for all locations. At the time a site is under investigation, it would be helpful to obtain even a short record of rainfall there. Such a record may be compared with the concurrent portion of a nearby long record and proper frequency values assigned to events in the short record, For example, a temporary gage might have a maximum hourly value of 0.60 inch some summer, and the same storm might produce the summer's maximum hourly value of 0.40 at a nearby long-record station. Similar comparison of other storms for the brief parallel record might confirm the ratio of 6 to 4 as an expression of the difference in the orientation, exposure, and elevation of the two stations.

This ratio could then be applied to the known 2-year, 1-hour value of the long-record station to get the estimated
2-year, 1-hour value for the short-record station, If the long-record station has a
2-year, 1-hour value for the construction site, it would be 6/4 of 0.5 or 0.75. Arrangements usually can be made for borrowtng a rain gauge for temporary use from the meteorological agency of the area in which the project is to be located.

## Infiltration

- If the upper surface of the permafrost
layer is deep and if provisions are made
for lower temperatures, design features
of a drainage system may be similar to
In permafrost areas, infiltration for design purposes should be considered zero. In

## Notes:

1. Observation of rainfall at National Weather Service stations provides the basic data for this figure. These stations are not located in the more elevated regions; consequently, wide deviations from the charted values may exist at altitudes above 2,500 feet. 2. The influence of local topographic characteristics should be taken into account and evaluated at the time of drainage design. 3. The lines of equal half-hour rainfall magnitudes correspond to the intensity-duration curves shown in Figure 6-64.

4. The once-in-50-years amount can be estimated by multiplying the once-in-2-years amount by the factor 2.2
ting of the soil at the interface between frozen and unfrozen ground.

those used in frost regions of the United States.

- Maintenance equipment for drainage
facilities should include heavy snowremoving apparatus and a steam boiler
with accessories for steam thawing of
structures which have become clogged
with ice. Pipes for this purpose are often fastened inside the upper portions
of culverts prior to their placement.

## Grading

- The flow of water in a drainage channel
has an accelerating effect on the thawing of frozen ground. This may cause the surface of the permafrost to dip considerably beneath streams or channels
which convey water. Bank sloughing
and significant changes in channel
grades become prominent. Sloughing is often manifested by wide cracks paralleling the ditches. For this reason, drainage ditches should be located as far as practicable from runway and road
shoulders.
Proper grading is a very important factor contributing to the success of a drainage system. The development of grading and drainage plans must be carefully coordinated. In arctic and subarctic regions, it is necessary to eliminate soft, soggy areas.

## Temporary Storage

- In many subarctic regions, freeing
drainage channels of drifted snow becomes a significant task before breakup
each spring. In these areas, it is advantageous to have ditch shapes and
slopes sufficiently wide and flat to accommodate heavy snow-moving equipment. In other locations where flow com
tinues year round, narrow, deep ditches
are preferable to avoid icings.
Trunk drains and laterals should have sufficient capacity to accommodate the project design runoff.

Do not consider supplementary pending above the drain inlets in airfield drainage designs for the arctics and subarctic. Formulate plans in sufficient detail to avoid flooding even during the time of actual construction.

## Icings

- Large, cut sections should be avoided in
planning the drainage layout. Thawed
zones or water-bearing strata may be en
countered and later cause serious
icings. Vegetative cover in permafrost
areas should be preserved to the maximum degree practicable. Where disturbed, it should be restored as soon as
construction permits,
- Inlets to closed conduits are commonly
sealed before freeze-up and opened prior to breakup each spring.
- Fine-grained soils immediately above a
receding frost zone arc very unstable.
Consequently much sliding and caving
is to be expected on unprotected ditch side slopes in such soils.
An *icing* is an irregular sheet or field of ice with no uniformity as to shape, thickness, or size. All icings are similar with regard to laminated structures, indicating that irrespective of shape, thickness, size, or cause, the actual process of formation is the same. Thin films of water traverse over layers of ice or other material and, when exposed to the cold air, freeze and form the first or an additional layer of ice. As water flow continues, the process is repeated, and an icing with horizontal laminations continues to grow until either the source of water supply is depleted or warmer weather begins.

## Types Of Icings

- Locating ditches over areas where permafrost lies on a steep slope should be
avoided if possible. Slides may occur because of thawing and consequent wet-
largely For the purpose of analysis, icings may be divided into three groups, depending on the nature of the source of water supply For icings formed along rivers or streams and adjacent areas having a source of water above or below the riverbed, the term river *icing* applies. If the source is Irom groundwater flow above permafrost, ground icing is the term most commonly used This term should not be confused with ground ice. which is often encountered in the arctic and subarctic as deposits in fine-graincd soils.

The term spring icing should be confined to when the source of wa ter is from subpermafrost levels or subpermafrost water under hydrostatic pressure. Spring icings are commonly large and thick.

Human activity can disturb the ground regime sufficiently to cause or accelerate the formation of all types of icings.

finds avenues of escape to the top of the ice via weak points, cracks, and fissures.

Here, exposed to the cold atmosphere, the water quickly freezes in thin sheets. This action is progressive, and icing continues to increase in thickness until the supply of water is exhausted or finds a new outlet, or until the beginning of warmer weather. A
bridge may shade the streambed and also prevent the deposition of snow. Freezing then would be more rapid beneath the bridge than at either upstream or downstream locations. Subsequent penetrations of frost would diminish groundwater -flow capacity at the bridge section and induce the formation of an icing above or at the site. These icings can be of various shapes and sizes, depending upon the valley topography, the depth of the snow, the intensity of cold, the water supply, and other factors.

River icings.

Most arctic and subarctic streams carry large loads of sediment which are not fed into the channels in uniform quantities Consequently, the rivers are quite wide and relatively shallow. Many rivers have a braided pattern of several smaller streams within the confines of the main channels.

These streams frequently shift in transverse position and often do so during one period of high flow. Winter flow is ordinarily very small and shallow. Freezing penetrates to the bottom of shallow streams quite readily, but the river dis- -
charge continues as groundwater flow beneath the riverbed. Because of thermal effects of flowing water, the soil below streambeds is unfrozen to greater depths than soil located elsewhere Consequently, It here is a large space for groundwater storage and flow above the permafrost and below all riverbeds.

The head motivating ground water flow is ordinarily quite large and can result in large pressures above secit ions where the groundwater flow is retarded.

Ground icings. Ground icings may take the form of mounds having considerable thickness but small areas. They may also form as crustations if groundwater flow is induced to the surface at points which are not of great lateral spacing but are of about equal elevation, In addition to a supply of water, there is another requisite to the formation of an icingan area where the water can be exposed to the cold atmosphere. A pavement kept clear of snow offers an excellent site over which flowing water can spread out into a thin film and then freeze. Icings from groundwatcr above the permafrost arc not likely to occur in the arctic, as the permafrost there is too close to the surface to permit any appreciable storage in the active layer. This occurrence is most severe in the southern zones of the subarctic and on slopes which face south. Groundwater flow may be induced to the surface in various ways. It is not essential that the seasonal frost reach the permafrost, although this very effectively blocks groundwater flow. Partial freezing of the active layer reduces the area of the section which ground water must pass. The path of least resistance may lead to the ground surface via a frost crack or fissure or through holes which have previously been made by burrowing animals Water coming to the surface in this way may flow Groundwater-flow retardation is a natural process at many river sections because river beds arc not homogeneous in water-carry -
ing capacity. Freezing of the water reduces channel area and capacity in some sections more than in others. The formation of anchor ice on the bottom of the streambed results in fur her constriction of the channel cross-section area. The water then

## 6-106 Drainage

considerable distances down slopes beneath a snow blanket without freezing.

stored as ice above the location of the bridge to be protected. The control of river icings then must be concerned with an insulation of streambeds at the critical section.

Various met hods have been tried to prevent
the occurrence of such icings. Some of
these have met with partial success. The
frost belt or dam has been advocated by
Russian investigators, but this method is
effective for only a few years. The thawing
in summer is accelerated at the site of the
frost dam, and eventually the permafrost
degrades sufficiently to permit groundwater
flow below the frost dam. Fences and bar-
riers have been used quite effectively under
special circumstances.

Ground icings.
                Ground icings can be con-
trolled to some extent by inducing the ice
to form upstream from the site in question.
This can be accomplished by the installa-
tion of frost belts. In open terrain, some
success can be achieved by merely keeping
snow removed from a strip crossing the af-
fected area in a direction transverse to
groundwater flow. Groundwater flow will
be blocked by freezing and forced to the sur-
face upstream from the cleared area. The
snow-free area also provides a cold space
on which surface flow can spread out and
freeze. If necessary, the depth of stored ice
can be increased by erecting some barrier
to the flow, such as an ordinary wooden-
stave snow fence on top of the ice initially
formed at the site of the frost belt. Be-
cause the process employs the removal of
snow, it is essential to shift the position of
the belt from year to year in order not to
unduly influence the depth to permafrost.
In timbered regions, it is obviously neces-
sary to maintain the frost belt at one loca-
tion to save the expense of tree removal.

Spring icings. Icings that occur from ar-
tesian, subpermafrost water and springs are
ordinarily quilt thick and cover consider-
able area. Reference is often made to the
icing in the Momy River Valley of Siberia.
This spring icing is about 15 miles long
and 3 miles wide, with an average thick-
ness of about 12 feet. It does not melt and
form each year. Spring icings can be con-
trolled quite readily. The temperature of
the water emerging from the ground is or-
dinarily quite high and the water does not
freeze quickly if confined to a conduit. In
some cases, an insulated conduit may be re-
quired to convey the spring water to loca-
tions where the formation of icing will do
no damage.

## Measures Against Icings

Spring icings.

If the source of water forming the icing is a spring, then it is necessary to resort to drainage or diversion to control the occurrence. This sometimes requires insulated channels. In the case of springs, flows are ordinarily too large to permit a storage of icc at or upstream from the site.

River icings. In the case of river icings, depths to permafrost are ordinarily too large to be blocked effectively by accelerated freezing such as is induced by the frost dam or
- bell, In addition, the subbed river flow is often in excess of what can be

## Fords, Dips, Causeways, And Bridges Fords Situation, And The Terrain Configuration

A ford is a shallow place in a waterway make its use necessary and practical.

where the bottom, either naturally or by human improvement, permits the passage An increase in water depth can close a ford for a considerable time. Streams in mounof personnel and vehicles. A ford is used tainous and desert country are subject to instead of a bridge when time limitations, the lack of structural materials, the tactical sudden changes in depth. The increase in depth can be so sudden as to endanger personnel or vehicles in the ford.

ly adaptable for improvement. In addition, the variation in the shape of the banks is not as pronounced in the reach area as it is at the bend.

Stream bottoms can be of such material that much effort is required to make fords usable.

## Reconnaissance

Bottom Material.

For a natural ford, the bottom material should be hard, durable, and interlocking.

Such material will resist cutting by wheeled traffic and erosion. The general terrain will determine the bottom condition, as follows:
Route reconnaissance should include the selection of possible ford sites. Special emphasis is placed on the requirements to be discussed in this section, Ford reconnaissance and required reports are covered in FM 5-36.

## Requirements

Z In mountainous country, sudden
freshet floods can transport large
boulders and stones along the bottom. This material is deposited at the passing of high water or at locations where
the widening of the stream reduces the
velocity. It may be necessary to remove
this material before traffic can cross the
ford,
The characteristics of a good ford are a slow current (usually less than 2 miles per hour); low, sloping banks; good approaches;
and a uniformly increasing bottom depth with a firm bottom material. Requirements of width depth, and bank slopes for fords are given in Table 6-23.

- In terrain of moderate or gentle slopes,
the velocity will tend to prevent deposi - tion of fine material. This tendency and
the scouring action of the water will
leave a good, firm bottom. The bottom
material may be disturbed by traffic and
will require protection.
Location. A desirable location for a ford is in the reach of the stream between bends.

At this location, the bottom depth is constant between the banks with only a slight channel in the center. The influence of river action on possible fording locations is
Z In slightly sloping or flat terrain, shown in Figure 6-66. Because of the increased velocity of the water, bends result streams meander and have low velocity.

in a deep channel that is difficult to im-
In addition, there is sometimes a high prove. In the reach, the center channel is water table. In such cases, the bottom not so deep or sharp and therefore is readimaterial may be very soft. Such in Figure 6-67, page 6-110, can be made by direct stream observation, as follows:
material will require a completely improved ford with special emphasis on bottom requirements, Timber, lumber, matting, gravel, or gabions can be used to improve trafficabilty.

Base Flow. Base flow is the normal flow that occurs in a stream when there has been no recent rain. The depth of this flow is dependent upon the quantity of ground water.

High-Water Determination. Table 6-23 indicates that a maximum water depth of 2 feet is allowable for truck traffic. To ensure maximum usc of the ford, it is necessary to determine the depth at which the stream will flow at frequently recurring times. Es-
High-Water Flow.

During the year, many rainfalls normally occur that cause flows above the base level, The velocity of such timates of various depths of flow, as shown flows generates a slight erosion cut, as This velocity would, in most cases, occur at low or moderate levels. Cross Section. Make a cross section of a ford location similar to Figure 6-66, page
6-109 and Figure 6-67. Include full details of bank slopes, bottom slopes, bottom variations, and water depth. In addition, determine the average velocity of the stream from measurements taken at equal intervals across the stream.

shown in Figure 6-67. The occurrence of such flows tends to prevent the growth of vegetation.

Since these flows can occur with relative frequency during the year, the depth of these flows could control the use of the ford. In the event the depth is greater in places than the fording depth of trucks (see Table 6-23, page 6-108), it may be necessary to fill these gaps with rock or gravel, However, such filling might cause the velocity of flow over the ford to be increased to the point that vehicles would have difficulty using the ford.

Channel Condition. Make a record of the character of the streambed. Include vegetation density and type, whether or not the channel is scoured, and the type of soil.

This information will determine the value of Manning's n.

## Construction

Flood Flow. In the absence of records, it is necessary to check stream banks for evidence of floodwater levels. The highest level of flood that occurs within a period of two years is of particular interest. The bend of a stream, especially with a high bank on the outside of the bend, would show an erosion cut that can be used to determine the flood level, as shown in Figure 6-67.

Two phases of construction are required for fordsthe development of the approaches and the preparation of the bottom.

Approaches.

Carefully note the height of the bank and the type of soil. This information helps to determine construction requirements.

Stream Velocity. The normal stream velocity at the fording site should not exceed 3 fps.

The maximum slopes for ford approaches should be as recommended in Table 6-23. Place material cut from the banks off to the side and not in the stream, where it may form an obstruction. Because traffic will wet the slopes and cause eventual deterioration, provision should be made for protecting the surface.

Determine the type of soil in the banks and bottom for construction requirements. In addition, note the size and type of bottom rock. This type of information gives an indication of the volume and velocity of flash floods which move or carry large material.

Ford-bottom preparation will depend upon site conditions.

Fill short, deep gaps with rock or gravel, preferably retained by wire mesh. Soft, mud bottoms can be improved by covering the bottom first with willow, brush mattresses, or timbers, and subsequently with metal planking, rock, or coarse gravel.

Even a hard and tenacious bottom deteriorates under traffic conditions and requires protective maintenance.

Consider these factors when raising the bottom of the ford:
Investigate the area, especially the banks, to determine the general flash-flood high watermark. This information on the area of the waterway, along with an approximation of velocity as indicated by the rock or other debris on the bottom, gives some indication of the volume of flow. This information will be necessary if bridging is required.

- The depth upstream from the ford increases in proportion to the amount of
rise of the bottom of the ford.

## Construction

- The velocity of flow over the ford increases at an increased fording depth so
that vehicles may be difficult to operate and control.
The subgrade should be of erosion-resistant material or a rock-compacted base, and it should be set between the cutoff retaining walls. The pavement should be of concrete or compacted macadam. The general construction is shown in Figure 6-68.

## Marking

Other factors of importance are as follows:
Place marking posts at each end of the ford and at as many intermediate points as may be necessary.

Mark a post at each end with an index to indicate depth. Warning notices should be clearly and prominently placed to alert drivers that flooding can occur suddenly and without warning.

- The site should be in the reach of the
stream and well away from any bends.
There is more erosion in bends than in
straight stretches. If a very severe flood
occurred, a structure placed in a bend
might be destroyed.

## Maintenance

- The structure should be set at right
angles to the flow to reduce scour.
Examine fords after each flooding. Repair scour damage upstream and downstream with riprap, Remove boulders and other debris to provide a clear passage for vehicles,

## Dips

Dips are paved fords used for the crossing of dry, wide, and shallow arroyos in semiarid regions subject to flash floods.

## Reconnaissance

The preferred location of a dip is in the straight run of an arroyo or wash, Determine the width between the banks and the top elevation of the banks. In addition, check the area above the dip site to determine if pending will occur and to what level.

Z The structure must be set at true drystreambed level to avoid scour erosion or silting. Under no circumstances
should the structure be set above drystreambed level.

## Marking

sited, carefully designed to pass the flow, and strongly built, It must incorporate a sufficient waterway at streambed level to permit the passage of the design volume of flow before the flood level reaches the top of the structure.

A typical design is shown in Figure 6-69, The main design features of a causeway follow.

The marking for dips is the same as for fords.

## Cross-Sectional Area Maintenance

A sufficient cross-sectional area must be provided to ensure that the flood level will not submerge the structure. Consider the following basic elements:
Dips, like fords, must be examined after each flooding, and scour damage upstream and downstream should be repaired with riprap, Remove boulders and other debris. When macadam is used, it can be anticipated that holes may be scoured in the roadway. Consider stockpiling rock adjacent to the area for immediate maintenance repair.

- The size and number of culverts or
other elements must be sufficient to
pass the flow.
When the water elevation
upstream and downstream is above the
culvert crown, pipe equations should be
used for flow design,

## Causeways

- The inverts or lowest parts of the culverts must be set at streambed level.
When it is essential to keep a roadway open during floods of medium intensity, a raised causeway can be used in place of a ford or dip, This type of structure must be well

Z The cover over the stream must be sufficient to protect the waterway against
traffic loads,

## Embankment

of the stream (Figure 6-66, page 6-109). In this location, there are moderate, even depths from bank to bank. The deep channel tends to be in the center. Abutments will be placed on the edge of the stream.

Because of the even distribution of flow, scour and erosion at the stream pier and bank abutments arc not expected to be so excessive as to cause maintenance problems.

## Height

Protect both the upstream and downstream faces of the embankment against scour and erosion. Heavy flooding or overtopping of the structure will require complete protection in the form of a concrete or rockgabion facing. To further prevent excessive scour and erosion, carry the protective facings below the streambed and provide them with aprons.

Anchor the ends of the structure securely into the banks in such a way that there is minimum obstruction to water flow.

The height of a bridge depends upon the flood-flow, high watermark. The height of that mark will determine the profile or su- -
perstructure level of the bridges as follows:

## Guardrails

Provide guardrails to guide and direct traffic. Because the structure can be overtopped, be sure to provide for ready replacement of the guardrails.

## Maintenance

Z When the flood-flow, high watermark is
above the banks, a high-profile or highlevel bridge must be constructed to keep the superstructure above the flood level. This type of bridge is well above bank level and may require a considerable length and height of approach.
Inspect the structure for scour or erosion after each flow (hat causes partial submergence or overtopping. Repair any damage immediately otherwise, at the next heavy flow, the structure could be destroyed.

Stockpiling of heavy rock and gabions at each end of a structure may be required.

Z When the flood-flow, high watermark is
below bank level. a low-profile or lowlevel bridge can be constructed. This
type of bridge presents fewer problems
than the high -level bridge, since approach ramps will not have to be constructed.

## Bridges Abutments

The location of bridge abutments depends upon an analysis of the flood level and the cross section of the stream (Figure 6-70).

Analysis proceeds as follows:
This section presents elements of bridge design other than the requirements for structural design Bridges must conform to the requirements of stream hydraulics in the same way as all cross-stream structures such as fords, dips, and causeways.

## Location

Abutments placed at 1A and 1B of Figure
6-70 present the most direct solution because they are located on high, dry ground, The location of a bridge should be away from bends in the straight section or reach Use of these locations, however, may necessitate more construction effort because of the increased length of the bridge. This increased length could result in the need for intermediate piers and spans. With this method, the full river waterway will be used for the passage of flood water.

## Drainage

Abutments placed at 2A and 2B would reduce construction time because fewer intermediate piers and spans would be required.

In addition, the fill in areas 1A-2A
and 1B-2B could be accomplished as the bridge is constructed. As can be seen from the figure, this placement reduces the cross section of the waterway, The following techniques could be used to accommodate this reduction in an available cross-sectional area:

Z The elevation of the bridge superstructure could be raised to account for the
rise in the flood level. In this case, use
substantial abutments that are well
protected against end scour.
The soil behind bridge abutments can become saturated because of rain or other conditions. This saturation can take place whether the approach road is at the natural grade of the soil or it is a filled approach. When saturation occurs, static hydraulic pressure on the back face of the abutment generates additional overturning movement. With wood abutments, this condition is relieved naturally.

However, if concrete abutments are used, the pressures can be relieved as follows:
Step 1.

Use weep holes to pierce the ments with bagged gravel backing on soil side.

- The superstructure elevation could be
left substantially at the original level,
and approach ramps over areas 1A-2A and 1B-2B could be constructed as
causeways to allow for flow. Care must
be taken to ensure that there is no excessive scour or erosion below the culvert outlet that would affect the roadway.
Step 2. Place gravel backing against the lower part of the abutment drained by a perforated pipe at the footing elevation. Set the pipe to drain out at the sides of the abutment.

Z The roadway approaches in areas 1A-2A
and 1B-2B could be depressed below the superstructure level. In this case,
the excess flood flow would pass over the roadway approaches, thus relieving

## Erosion Control

reduce the need for extensive erosion control measures. However, additional control is usually required.

Most methods of control are based on dissipating the energy of water, providing an erosion-resistant surface, or some combination of these techniques. This chapter acquaints the military engineer with the means available to reduce or eliminate the erosive force of water.

Erosion must be controlled to maintain an effective and clear drainage system with a minimum of maintenance and to reduce hazardous dust conditions. Erosion may occur at any point where the force of moving water exceeds the cohesive strength of the material with which the water is in contact.

Proper design of side slopes in cut and fill sections (based on the type of soil) will

## 6-114 Drainage

the bridge flow.

If this action is taken, the roadway may not be usable at all times. Since overflow is anticipated, the construction of these approaches is similar to construction of causeways without the culverts. If the bridge is designed properly, with fording depths as outlined in Table 6-23, page 6-108, it may be usable during floods under extreme conditions.

Z
When a depressed roadway or an elevated superstructure is used, the approach to the bridge must have a gentle
slope to prevent vehicle impact on the
abutment and to ensure traffic visibility.
abutthe

## Nonuse Areas And Open Channels

disturbed soil in place. Vertical spacing and longitudinal gradients of terraces are given in Figure 6-71.

## Turfing

Terracing is a control measure designed to dissipate the energy of overland flow in nonuse areas.

Turfing, paving, Gunite lining, and placing riprap are control methods designed to cause turbulence and to increase retardation, thereby dissipating the energy of flow in open channels such as ditches and pjpe outfalls. In cases where even riprap will be eroded, the use of gabions is a speedy and relatively inexpensive means of dissipating energy.

Ditches are often protected by placing strips of sod (held in place by wooden boards or stakes) perpendicular to the flow path at intervals along the ditch, as shown in Figure 6-72.

## Terracing Paving And Gunite Lining

A terrace is a low, broad-based earth levee constructed approximately parallel to the contours of the topography. A terrace either intercepts and holds the water until it infiltrates the soil or moves it as overland flow to a suitable discharge point. A hardy, vigorous turf should be planted to hold the Ditches having grades in excess of 5 percent usually require paving or a Gunite lining. Where a slope equals or exceeds 5
percent, paving must be extended down slope at least to the point in the ditch at which the erosive energy of the water is controlled or absorbed without erosion damage.

Paving with either asphalt or portland-cement concrete provides superior erosionresistant linings in gutters, ditches, and outfall structures.

Consideration must be given to the selection of an adequate size of stone, the use of adequately graded riprap, the provision of a filter blanket, and the proper treatment of the end of the riprap blanket.

## Selection Of Size

Curves for the selection of stone size required for protection, with Froude numbers and depths of flow in the channel shown, are shown in Figure 6-73.

Gunite lining of ditches controls erosion effectively. Gunite is a mixture of portland cement and sand with water added just before the mixture is sprayed from a highpressure nozzle onto the surface being protected.

The Gunite lining is formed over steel mesh placed over the bottom and sides of the ditch. Gunite is sprayed to a thickness of 1 to 1 1/2 inches, with the steel mesh located midway in the thickness.

Human resources, time, material and equipment expenses usually limit the use of paving or Gunite linings to only the most demanding conditions in TO airfield construction.

Two curves are given.

One is for riprap subjected to direct flow or adjacent to hydraulic structures such as side inlets, confluences, and energy dissipators, where turbulence levels are high. The other is for riprap on the banks of a straight channel where flows are relatively quiet and parallel to the banks.

## Placing Riprap

With the depth of flow and average velocity in the channel known, the Froude number can be computed from the following equation:
value can be determined from the appropriate curve.

Riprap protection should be provided adjacent to all hydraulic structures. When placed on erodible surfaces, it prevents scour- al the ends of the structure. This protection is required on the bed and banks for a sufficient distance to establish velocity gradients and turbulence levels at the end of the riprap.

Curves for determining the riprap size required to prevent scour downstream from culvert outlets with scour holes of various depths are shown in Figure 6-74, page
6-118. Make the thickness of the riprap blanket equal to the longest dimension of the maximum size of stone or 1.5 times whichever is greater.

Riprap can also be used for lining the channel banks to prevent lateral erosion and undesirable meandering. Provide an expansion either horizontally or vertically (or both) immediately downstream from hydraulic structures such as drop structures or energy dissipators. The expansion allows the flow to expand and dissipate its excess energy in turbulence rather than directly on the channel bottom and sides.

Riprap has been known to fail fromfrom When the use of large rock is desirable but impractical, substituting a grouted reach of smaller rock in areas of high velocities or turbulence may be appropriate. Grouted riprap should be followed by an ungrouted reach.

Z Movement of the individual stones
a combination of velocity and turbulence.
- Movement of the natural bed material
through the riprap, resulting in slumping of the blanket.
A well-graded mixture of stone sizes is preferred to a relatively uniform size of riprap. A recommended gradation is shown in Figure 6-75, page 6-119. In certain locations, the available material may dictate the gradation of riprap to be used. The

- Undercutting and leveling of the riprap
from scour at the end of the blanket.

## 6-116 Drainage

gradation should resemble the recomplot. If the gradation of the available riprap mended mixture as closely as possible.

is such that movement of natural material Consider increasing the thickness of the through the riprap blanket would be likely, riprap blanket when locality dictates using place a filter blanket of sand, crushed rock, gradations with a larger percentage of small gravel, or synthetic cloth under the riprap.

stone than shown by the recommended The usual blanket thickness is 6 inches, although a greater thickness is sometimes necessary.

the riprap blanket.
                     However, the extra ef-
fort required to provide gradual reduction
in riprap size is seldom justified. Double
the thickness of the riprap blanket at the
downstream end to protect against under-
cutting and unraveling. An alternative is a
rubble blanket of constant thickness and
suitable length, dipping below the natural
streambed to the estimated depth of bottom
scour.

Design
An ideal riprap design would provide a
gradual reduction in riprap size until the
downstream end of the blanket blends with
the natural bed material. Unless this is
done, turbulence caused by the riprap is
likely to develop a scour hole at the end of

## 6-118 Drainage Description And Assembly Gabions

Gabions are large, steel, wire-mesh baskets, usually rectangular and variable in size, designed to solve erosion problems at a low cost, Widely used in Europe, gabions are now accepted in the United States as a valuable and practical construction and main -
tenance tool. They can be used in place of sheet piling, masonry construction, or cribbing.

Gabions are supplied from manufacturers in flat, folded bundles. For ease in handling and shipping, the number of gabions per bundle varies according to the size of the gabions. The box gabion is a rectangular cage or basket formed of woven, hexagonal, galvanized steel, wire mesh with
4- to 8-inch openings and divided by diaphragms into cells.

To assemble, remove a single gabion from the bundle and unfold it on a hard, flat surface to straighten unnecessary creases and kinks. Fold the being stretched, inspect all corners to make sure the lacing is secure and the corners are closed.

Keep gabions taut while they are being filled with stone.

front, back, and end panels to a right angle to form a box, as shown in Figure 6-76.

Securely lace the vertical edge and diaphragms with binding wire, Where water, soil, and atmospheric conditions allow, galvanized wire mesh can have a life of 40 years or more, For soils and water showing a pH factor of less than 7 or more than 12, plastic-coated wire must be used to form gabions.

## Filling Procedures

The best filling material is one that allows flexibility in the structure and, at the same time, fills the gabion compartments with a minimum of voids and maximum weight. Ideally, the stone should be small, just slightly larger than the size of the mesh (usually 4 to 8 inches). The stone should be clean, hard, durable, and resistant to weathering and frost action.

Fill the gabions to a depth of 1 foot. Then place one connecting wire in each direction and loop around two meshes of the gabion wall, as shown in Figure 6-77. Repeat this operation twice or until the gabion is filled;
then fold the top shut and wire it to the ends, sides, and diaphragms.

## Installation

Pack the stone inside the compartment as tight as practical, To protect the vertical diaphragm during the filling operation, temporarily place rebars and lace them along the upper edges.

Before placing the gabions, make the ground surface relatively smooth and even.

Place the assembled gabions in position singly or wired together in groups suitable for handling. It is convenient to place the gabions front-to-front and back-to-back to expedite the stone-filling and lid-lacing operation.

Lace the basket along the perimeter of all contact surfaces. Where there is more than one course of gabions, the base of the empty gabions placed on top of a completed row must be tightly wired to the latter as shown in Figure 6-77.

Some manual stone adjustment is required during the filling operation to prevent undue voids.

Fill the gabion slightly overfull and allow for subsequent settlement;
then lace the lid down with binding wire to the tops of all the sides and to the tops of the diaphragm panels. Since it is necessary to stretch the lid to fit the sides exactly, use a short crowbar or special tool designed for this purpose.

When using 3-foot-high gabions, place them empty and lace for approximately 100 linear feet. Anchor the first gabion firmly and apply tension to the other end with a comealong or by other means to achieve the proper alignment.

Anchoring can be accomplished by partially filling the first gabion with stone.

While the gabions are The strong interconnection of all units in a gabion structure is an important feature. It is essential that the lacing be done properly. Adjoining gabions are wired together by their vertical edges. Empty gabions,

## 6-120 Drainage

stacked on filled gabions, arc wired to the filled gabions at front and back. Gabions may be filled by almost any type of earth-handling equipment such as a payloader, crane, conveyor, or modified concrete bucket. The use of rounded stone, if it is available, reduces the possibility of damage to the galvanized wire during mechanical filling.

When the depth of the water is too great for the gabions to be filled on site, fill them at a dry location nearby and place them underwater by crane or barge,

## Maintenance And Repair

Maintenance and repair are simple procedures; therefore, gabions are inspected at least once a year. Holes can be patched with small panels of mesh, and broken wires can be repaired by using the method shown in Figure 6-78.

## Thickness

Gabion-lined channels may be designed using Manning's equation and the procedures for open -channel design.

Uses Gabions can be used in the following ways:
The thickness of gabions may be calculated by considering the gradient of the channel, the steepness of its slope, the type of material forming the banks and bed, and the curvature of its course.

A 12-inch-deep lining is suggested for channels having reasonably straight alignment, side slopes of less than 35 degrees, and a flow velocity of about 10 fps, as shown in Figure 6-79.

Use an 18-inch gaion lining for curved channel sections with a side slope of 45
degrees. Use 36-inch stepped-back gabion protection for sharper side slopes. For a steep channel slope, a combination of lining and weirs may be required.

- Protective and antierosion structures on
rivers (for example, revetments, groins, or spurs).
- Other antierosion structures (for example, weirs, drop structures, and check dams).
Z Channel linings.
In the case of easily erodible soil, a layer of filter material or permeable membrane of cloth woven of synthetic fibers is required.

The gabion should be filled with stone small enough to allow at least two overlapping layers,

- Seashore protection. - Low-water bridges or fords.
- Culvert headwall and outlet structures.
In designing a gabion-lined channel, the roughness factor or coefficient (n) in Manning's formula may be assumed to be between 0.025 and 0.030, If the gabions are grouted, the roughness factor can be assumed to be between 0.012 and 0.018.

- Bridge abutments and wing walls.
It is often necessary to modify the jnlet and outlet of a culvert by using transition structures to reduce entrance losses and to inhibit erosion. Therefore, the two most common devices for which gabions are used are headwalls and outlet aprons.

Headwalls or wing walls are designed to protect the slopes of an embankment against scour, to increase culvert efficiency by providing a flush inlet as opposed to projecting one, to prevent disjointing of sectional-pipe culverts by anchoring the inlet An apron is often required at the outlet of a culvert to reduce the outlet velocity and thereby inhibit scour. Gabions are well adapted for use here because of their roughness, flexibility, and durability. See Figure
6-80.)
Table 6-24 indicates the type of gabion protection required for various ranges of outlet velocities and outlet, and to retain the embankment slope. These structures are built in a variety of shapes: straight, L-shaped, flared, and warped. A typical plan using a headwall and an outlet apron with a culvert is shown in Figure 6-79. Straight headwalls arc generally used on small, roadside culverts under driveways and in small channels having a low approach veloc ly. They arc also recommended where there is a ten dency for lateral erosion to develop at the outlet.

## Culvert Outlets

Can tilevered culvert outlets may be used to discharge a free-falling jet onto the bed of the outlet channel. As a result, a plunge pool will be developed. The depth and size of the plunge pool depend on the energy of the falling jet at the tailwater and the erodibility of the bed material.

Most culverts operate under free outfall conditions (that is, there is no control of tailwater), and the discharge possesses kinetic energy in excess of that occurring naturally in the waterway. This excess kinetic energy must often be dissipated to control damaging erosion. The extent to which protective works are required for energy dissipation depends on the amount of excess kinetic energy and the characteristics of the material in the outlet channel.

In general, scour occurs at average velocities in excess of about 1.5 fps in uniform-graded sand and cohesionless silts, 2.5 fps in wellgraded sand, 3.0 fps in silty sand, 4.0 fps in clay, and 6.0 fps in gravel. These velocities should be used only as a general guide.

Outlet headwalls and wing walls serve the dual purpose of retaining the embankment and limiting the outlet transition boundary.

Erosion of embankment toes can be traced to eddy attack at the ends of such walls. A flared transition is effective if it is proportioned so that eddies induced by the effluent jet do not continue beyond the end of the wall or overtop a sloped wall.

As a guideline, it is suggested that the product of velocity and flare angle not exceed 150 degrees.

For example, if effluent velocity is 5 fps, each wing wall may flare
30 degrees; but if velocity is 15 fps, the flare should not exceed 10 degrees. Unless wing walls can be anchored on a stable foundation, a paved apron between the wing walls is required. Special care must be taken in the structure design to preclude undermining.

If possible, make a study of local material to determine its erosion tendencies prior to a decision on the degree of protection required. The study should consider three types of outfalls offering three degrees of protection: plain outlets, transitions, and stilling basins.

Plain outlets provide no protective works and depend on natural material to resist harmful erosion. Transitions provide little or no dissipation on the works themselves but result in a spreading of the effluent jet to approximate the crosssection flow of the natural channel, thus reducing the concentration of energy prior to releasing the flow to the outlet channel.

Stilling basins result in dissipation of energy on the protective works.

## Plain Outlets

A newly excavated channel may be expected to degrade, Proper allowance for this action should be included in establishing the apron elevation and depth of cutoff wall.

Warped end walls provide excellent transitions that result in the release of flow in a trapezoidal cross section which approximates the cross section of the outlet channel.

A warped transition is made at the end of the curved section to reduce the possibility of overtopping as a result of su - perelevation of the waler surface. A paved apron is required with warped end walls.

Riprap is usually required at the end of a transition-type outlet.

If the discharge channel is in rock or a material highly resistant to erosion, special erosion protection is not required. This type of outlet should be used only if the material in the outlet channel can withstand velocities about 1,5 times the velocity in the culvert, At such an outlet, side erosion from eddy action or turbulence is more likely to prove troublesome than bottom scour.

## Transitions Stilling Basins

device should be considered. Three types of dissipators which may offer a solution are the hydraulic-jump stilling basin, with details developed at the St, Anthony Falls Hydraulic Laboratory; the impact-energy dissipator, with details developed at the hydraulic laboratory of the Bureau of Reclamation; and stilling wells, These dissipa tors are beyond the scope of TO construction, Design procedures are not ineluded in this manual.

At culvert outlets where a high concentration of energy or easily eroded materials make excessive erosion likely, a stilling basin or other energy-dissipating device is required. For TO construction, riprap or simple, concrete stilling basins are usually required. There are many types of energydissipating devices such as hydraulic-jump basins, roller buckets, flip buckets, impactenergy-dissipating devices, and stilling wells. In unusual cases involving major structures, the use of a special type of Measuring Trafficability Self-Propelled, Tracked Vehicles and All-Wheel-Drive Vehicles Negotiating Slopes Trafficability Data Critical Layer Soils Trafficability Soil-Trafficability Classification Instruments and Tests for Trafficability Application of Trafficability Procedures in Fine-Grained Soils and Remoldable Sands Basic Trafficability Factors Operation in Coarse-Grained Soils
7

## Soils Trafficability

Soils trafficability is the capacity of soils to support military vehicles. This chapter in cludes information on the following topics:

- Operating and maintaining the soil-trafficability test set.
Z Measuring trafficability with the results of the tests performed by the cone penetrometer and remolding equipment.

Z Making trafficability estimates from terrain data (topography and soil data) and weather conditions.

The procedures in this chapter are conservative estimates for field use. Engineers must be cautious as the calculated results can vary by 20% or more from changes in tire pressure and deflection. Plan for the unexpected!

This chapter discusses the trafficability of fine- and coarse-grained soils. Organic soils
[muskeg.) and snow are not discussed. The trafficability of fine-grained soils (silts and clays) and sands that contain enough fine-grained material to behave like fine-grained soils when wet is more difficult to assess than trafficability in coarse-grained soils (clean sands). Relationships that describe the soil-vehicle interactions are based on soil shearing-resistance measurements made with the cone penetrometer and corrected for soil remolding under vehicle traffic by the remolding index [RI) procedures.

The information presented in this chapter is limited to problems associated with soils.

It does not include problems associated with natural or man-made obstacles (such as forests or ditches) nor Information on vehicle characteristics (such as the maximum tilt or side angle at which a vehicle can climb without power stall or overturning), The basic principles for the procedures presented are sound for temperate and tropical climates and for soils that have been subjected to freeze-thaw cycles, if they are not frozen at the time of testing and passage of traffic.

Originally, this chapter was designed to permit calculation ns of trafficability by field personnel with only a hand-held calculator.

Performances were estimated for a minimum number of vehicle passes (1) or a maximum of 50 vehicles in the same ruts, Today most relations are used for one pass and the combined effects on vehicle performance of terrain features such as soil, vegetation, and slope can only accurately be determined through the use of the computerized Army mobility prediction system contained in the NATO Reference Mobility Model (NRMM). The engineering relationships which produce vehicle speed predictions or GO/NO GO performance based on measured terrain and vehicle characteristics are contained in the NRMM. This chapter only introduces fundamental relationships, terminologies, and illustrations of this computerized, comprehensive mobility evaluation tool.

Most military units have access to NRMM
relationships through personal computer-based NRMM versions of mobility predictions such as the Comprehensive Army Mobility Modeling System (CAMMS).

## Basic Trafficability Factors Slipperiness

The following factors impact soil trafficability:

## Soil Strength

Excess water or a layer of soft, plastic soil of low LL overlying a firm layer of soil can produce a slippery surface. Such a condition may make steering difficult or may immobilize rubber -tired vehicles.

Vegetation, especially when wet and on a slope, may cause immobilization of rubber-tired vehicles.

Slipperiness is troublesome, even when associated with soils with high-bearing capacities.

## Variation Of Trafficability With Weather

Bearing and traction capacities of soils are functions of their shearing resistance.

Shearing resistance is measured by the cone penetrometer and is expressed in terms of cone index (CI). Because the strength of fine-grained soils (silts and clays) may increase or decrease when loaded or disturbed, remolding tests are necessary to measure any loss of soil strength expected after traffic. The finegrained soil CI multiplied by the RI
produces the rating cone index (RCI) used to denote soil strength corrected for remolding. A comparison of the RCI with the vehicle cone index (VCI) indicates whether the vehicle can negotiate the given soil con -
dition for a given number of passes. For example, if a soil has a CI of 120 and an RI of 0.60 in its critical layer, the soil strength may be expected to fall to 120 times 0.60, or an RCI of 72, under traffic. Therefore, such soil is not trafficable for vehicles with VCIs greater than 72. If a vehicle has a minimum soil-strength requirement of 72 for one pass, its        is 72 and an RCI of
72 is required for the vehicle to complete one pass without immobilization. Appendix D of this manual summarizes VCIs for military vehicles.

## Stickiness

Weather changes produce changes in soil trafficability. Fine-grained soils increase in moisture during rainy periods. This results in slipperiness, stickiness, and decreased strength. Dry periods produce the opposite effects.

Loose sands improve trafficability through an increase in cohesion during rainy periods and return to the loose, less trafficable state during dry periods. Trafficability characteristics measured on a given date cannot be applied later unless full allowance is made for the changes in soil strength caused by weather. Freezing and thawing conditions can cause extreme variations in the trafficability of soils.

Several inches of frozen soil may carry a large number of extremely heavy vehicles.

However, when this same material is thawing, it may be impassable to nearly all vehicles. Snow cover can have a significant t effect on the depth of freezing. The absence of snow allows frost to penetrate more deeply into the soil. Techniques have been developed for predicting the effects of weather on soil trafficability. These techniques are part of the comprehensive NRMM and are not included in this publication.

Stickiness may seriously hamper vehicles operating in wet, fine-grained soil. Under extreme conditions, sticky soil can accumulate in a vehicle's running gears, making travel and steering difficult. Normally, stickiness is troublesome only when it occurs in soils of low-bearing capacity (normally, fine-grained soils).

## 7-2 Soils Trafficability Critical Layer

weight, and the Table 7-1 sumcommon The critical layer is the layer in the soil profile, the vehicle type and that supports the weight of the vehicle in number of passes required.

question. The critical layer's depth varies marizes these variations for with the soil type, the soil's strength military vehicles.

## Instruments And Tests For Trafficability

This section contains general information regarding the soil-trafficability test set. The specific use, operating instructions, and test procedures for the soil-trafficability test set are described in detail in Appendix E of this manual.

Sieve-analysis tests, plasticity tests, and other field identification tests arc described in Chapter 2 of FM 5-530. Trafficability measurements are made with the soil-trafficability test set. This set consists of one canvas carrying case, one cone penetrometer with 3/8-inch steel and 5/8-
inch aluminum shafts and a 0.5-squareinch cone, one soil sampler, remolding equipment (which includes a 3/8-inch steel shaft and a 0.2-square-inch cone, a 5/8- inch steel shaft with foot and handle, a 2
1/2-pound hammer, a cylinder and base with pin), and a bag of hand tools. The items are shown in Figure 7-1 in their proper places in the carrying case. The set is carried on the back as shown in Figure 7
2, page 7-4. The complete set weighs 19
pounds.

The primary instrument of the soil-trafficability test set is the cone penetrometer.

It is shown in Figures 7-3 and 7-4 and Figure 7-5, page 7-5.

It is used to determine the shearing strength of low-strength soils.

There is also a dynamic cone penetrometer, but this instrument is used to determine shear strength of high-strength soils such as those found in the base courses of roads and airfields. (The dynamic cone penetrometer is currently developmental and has only limited fielding.) The dynamic cone penetrometer is described in detail in Appendix E. The cone penetrometer consists of a
30-degree cone with a 1/2-inch-square base area, a steel shaft 19 inches long and 3/8
inch in diameter, a proving ring, a micrometer dial, and a handle. When the cone is forced into the ground, the proving ring is deformed in proportion to the force applied.

## 7-4 Soils Trafficability

remolding tests in remoldable sands. The cone penetrometer cannot be Used to measure gravels.

Gravels arc considered excellent for 50 passes, and any problems can be determined by visual observation.

The specific use, operating instructions, and test procedures for the cone penetrometer as well as the remainder of the soil-trafficability test set are described in detail in Appendix E.

The amount of force required to move the cone slowly through a given plane is indicated on the dial inside the ring. This force is an index of the soil's shearing resistance and is called the soil's CI in that plane.

The dial's range is 0 to 300 pounds per square inch (psi). (The actual load applied to the cone penetrometer is 0 to 150 pounds, since the instrument uses a 1/2-
square-inch base.) The proving ring and handle are used with a 3/8-inch-diameter steel shaft and the 0.2-square-inch cone for

## Measuring Trafficability

bility evaluation, to classify large areas as above or below the critical range without extensive testing.

## Number Of Measurements

Whenever reconnaissance parties have time to take trafficability measurements, they should obtain data to determine the number and type of vehicles that can cross the area and the slopes they can climb. The procedures for measuring trafficability are described in this section. Remember that measurements are valid only for the time of the measurement and short periods thereafter, provided no weather changes occur.

## Range Of Cone Indexes

The number of measurements taken is determined by the time available, the judgment of the range of soil strengths, and the general uniformity of the area. Trafficability-measuring instruments are designed for rapid observations. The accuracy of the average of any series of readings increases with the number taken. Variations in soft soils require that at least 15 readings be taken to establish a true average CI at any spot at a given depth. The 15 readings should be distributed throughout a uniform area, A CI ranging between 10 and 300 in the critical layer is required to support most military vehicles. Except for a few vehicles, a CI below 10 is considered to be a nontrafficable area and a CI above 300 is considered trafficable to all but a few vehicles for 50 passes. These limits usually make it possible, while gathering data for traffica-
If time is not available to take a large number of measurements, use judgment to reduce the number according to the following instructions:
Example:
Using the work sheet in Figure 7-6, five tests down to 24 inches were completed at a selected site. The corresponding penetrometer readings are listed in the blocks for the corresponding depth and test. For example, in test number 1 the 0-inch reading is 58, the 6-inch reading is 63, and so on. The individual depth readings are then added and averaged, as in the 0-inch layer. (Always round down.) Solution:

- If CIs are between 0 and 150, enough
readings should be taken to assure accurate coverage of the area. Readings should be made at enough locations to establish the area boundaries and the
average CI within close limits. Four to
six sets of readings should be made at
each location. Remolding tests (in the case of fine-grained soil and remoldable
sand) should be run at a sufficient number of locations to establish the range of RIs If a tentative route can be selected
in the field, penetrometer and remolding
measurements should be made at closely spaced intervals to locate any
soft spots. Where CIs are less than 10,
readings should be limited to the number needed to establish the nontrafficable-area limits. No remolding tests are required.
The numbers in the numerator are the individual readings.

The number in the denominator represents the number of tests conducted. The resulting quotient is the average CI for that depth.

After all individual readings are added together, they are averaged with the reading above and below to obtain the average CI
for that layer.

In the case of the 0- to
6-inch layer, the 66 and 71 are added and then averaged [68). The 68 is the CI for the 0- to 6-inch layer, Readings are then averaged for the 6- to 12-inch layer and so on.

- If the CI ranges from 150 to 200, select
enough locations to verify the area limits. Three or four sets of readings
should be made at each location. For fine-grained soils and remoldable
sands, remolding tests should be made
at the first two or three locations. If
these show an RI of 0.90 or more, additional remolding tests are not needed.
If the RI is below 0.90, sufficient remolding tests should be made to establish
the range for the area. This can be established with tests at approximately
six locations.

NOTE: Intermediate values for the 3-,
9-, and 15-inch depths (fine grains and re-
moldable sands) can be interpolated when
the vehicle types under consideration re-
quire them.

Z
If the CIs are above 200, a few penetrometer readings will usually verify the
extent of the area. Two sets of profile readings taken at each location should be adequate. Remolding tests on soil
from the critical layer (fine-grained soils
and remoldable sands) should be made
at the first two or three locations. If
these show an RI of 0.80 or more, no additional remolding tests are needed.
Sufficient tests should be made to estab-
Continuing with the example above, the M929 dump critical layer for one vehicle and for 50 vehicles is 9-15 inches. (To determine the critical layer, refer to the section on critical layers in this chapter, page
7-3.) Because the readings on the cone penetrometer are taken at the 0-, 6-, 12-,
18-, and 24-inch depths, the 3-, 9-, 15-, and
21-inch readings must be interpolated where necessary.

## 7-6 Soils Trafficability

lish the range for the area if the RI is below 0.80. This can be established with tests at approximately four locations.

To find the 3- to 9-inch layer, the ]CI readings for the 0- to 6-inch and the 6- to 12-
inch layers are added together and then averaged:
shown in Table 7-2. CIs should be measured at 6-inch increments down to 18
inches in the early stages of area reconnaissance. If these measurements consistently reveal that the profile is normal, only readings in the critical layer need to be recorded.

70 becomes the CI for the 3- to 9-inch layer. For the 9- to 15-inch layer, the 6- to
12-inch and 12- to 18-inch layers will be interpolated:
The CI for the 9- to 15-inch layer is 74.

## Strength Profile

For a tracked vehicle weighing less than
100.000 pounds, such as the M113A3 armored personnel carrier (APC), readings are recorded for the 6- and 12-inch depths. In a normal profile, remolding tests should be run only on samples taken from the normal critical depth for the vehicle in question, since a decrease in RI with increasing depth is not common.

The RCI for this layer is used as the criterion of traffic ability for this particular vehicle.

## Normal Strength Profile In Fine-Grained Soils And Remoldable Sands

Abnormal Strength Profile in Fine-
Grained Soils and Remoldable Sands An abnormal strength profile has at least one CI reading that is lower than the reading immediately preceding it. An area with In a soil with a normal strength profile, the CI readings either increase or remain constant with each increment of depth. An area with a normal strength profile is

## 7-8 Soils Trafficability

an abnormal strength profile is shown in Table 7-2.

When an abnormal strength profile exists, CI readings should be made and recorded at 6-inch increments from the top of the normal critical layer (6-inch depth for the M113A3 APC) to 6 inches below the bottom of the normal critical layer (18 inches for the M113A3 APC).

normal profile, a remolding test was run only for the 6- to 12-inch layer. The RCI for area A is 60 (the average of 50 and 70)
x 0.90 = 54. In area B, remolding tests were necessary for both the 6- to 12-inch and 12-to 18-inch layers. In this area, the RCI of the 6- to 12-inch layer is 60 (the average of 75 and 45) x 0.90 = 54, and the RCI of the 12-to 18-inch layer is 40 x 0.90 = 36. The RCI of the 12- to 18-inch layer, 36, is the governing value for the trafficability in area B.

Example:
Using the work sheet in Figure 7-6, page 7-7, the critical layer for one or 50 M929 dumps is 9 to 15 inches.

Remolding tests must be run on samples from the normal critical layer and also from the 6-inch layer below it. The lower RCI is used as the trafficability measurement. Lowground-pressure tracks are an exception to this rule. The 3- to 9-inch layer is always used as the critical layer for these vehicles.

## Strength Profile In Coarse-Grained Soils

Samples are removed from the critical layer.

For the 9- to 15-inch layer, three tests were conducted, each yielding different results.

The average of these results is determined, and this number becomes the RI for that layer.

As indicated in Table 7-1, page 7-3, the critical layer for most vehicles in coarsegrained soils is the 0- to 6-inch layer. Most coarse-grained soils have a normal strength profile with a large increase in strength with depth when compared to fine-grained soils. For this reason, CI measurements should be taken at 3-inch increments to 18
inches or until the maximum capacity (300 CI) of the penetrometer has been reached.

(1.14 exceeds 1.0, so use 1.0.) The      is 74 and the       is 74. The          is 30, and the       is 68. Comparing the to the           and the              to the           it is determined that one M929 dump can cross the area and 50 M929 dumps also can cross the area because the RCI values are greater than or equal to the VCI values.

Usually, fewer penetrations are required to establish an average because coarse -grained soil areas generally are more uniform than fine-grained soils and remoldable sands.

The RI tests are not required. The strength measurements in a coarse-grained soil area are shown in Table 7-2.

Usually a mixture of vehicles will pass through an area, not a column of one vehicle type.

Therefore, the VCI and critical layer will be determined for the critical vehicle.

## Rating Cone Index

To estimate how many vehicles will cross an area when the RCI is less than the         or to see what the VCI for less than 50 vehicles will be, use the following formula:
The RCI defined earlier is the CI that will result under traffic. This value is compared to the VCI to determine the trafficability of the area for a specific vehicle, Example:
will give an increment for one vehicle that, when added to the        will give the AVCI for any amount of vehicles up to 50.

The following fine-grained soil areas are to be investigated for trafficability for vehicles with a normal critical layer of 6 to 12
inches. Because area A in Table 7-2 has a Example:
ticity of the soil, the more severe the effects of stickiness. Stickiness adversely affects the speed and control of all vehicles but will not cause immobilization except for the smallest tracked vehicles. The worst stickiness is nothing more than a nuisance to larger, more powerful military vehicles. Removing fenders will reduce stickiness effects on some vehicles. Instruments for measuring the effects of stickiness on the performance of vehicles have not yet been devised.

Estimate how many M1A1 tanks can cross a level area with fine-grained soil where the CI is 65 and the RI is 0.80 in the critical layer. For simplicity, we have used this approach on trafficability research. In actuality, the strength increment decreases as passes increase; for example, more strength is required for lower passes than for higher passes, so that more remolding occurs at lower passes than at higher passes. The differences are not linear but can be estimated in the manner shown here.

## Slipperiness Each Vehicle Adds 0.66 To The

Like stickiness, the effects of slipperiness cannot be measured. Soils that are covered with water or a layer of soft, plastic soil usually are slippery and often cause steering difficulty, especially in rubber-tired vehicles. Immobilization can occur when slipperiness is associated with low-bearing capacity. The adverse effects of slipperiness are more severe on slopes. Sometimes slopes with adequate soil strength will not be passable because of slipperiness.

Chains on rubber-tired vehicles usually improve mobility in slippery conditions. The following categories are used to rate slipperiness:

Condition
Symbol
Not slippery under any conditions
N
Slippery when wet
P
Slippery at all times
S

To estimate the number of vehicles that can pass, add 0.66 to    until the number is equal to the RCI or one more increase will exceed the RCI. (Remember, this is only an estimate.)

## Vegetation Other Trafficability Evaluation Factors

In addition to the CI of an area, consider the factors that follow when evaluating traffixability. Slope The effects of vegetation on trafficability are not within the scope of this manual, but some points are worthy of mention, Dense grass, especially if wet, may provide slippery conditions. Additionally, soil strength requirements will be greater than normal if small trees or thick brush must be pushed down by the vehicle.

## Organic-Soil Areas

The steepest slope, or ruling grade, that must be negotiated should be determined by studying a contour map. For travel over slopes, the CI requirements must be increased over those required for level terrain.

## Stickiness

Much of the terrain in northern latitudes is blanketed with a layer of organic material composed of roots, mosses, and other vegetation in various stages of decomposition, Limited testing with military vehicles reveals that low-ground-pressure, tracked Stickiness occurs in all fine-grained soils when they are wet.

The greater the plas-

## 7-10 Soils Trafficability

well defined as for fine-grained and coarsegrained soils.

## Other Obstacles

vehicles, such as the M973 small-unit support vehicle (SUSV), can travel 50 passes over organic mats that are more than 6 inches thick.

A complete assessment of the traffic ability of a given area must include an evaluation of obstacles such as forests, rivers, boulder fields, ditches, and hedgerows. Exact effects of such obstacles on the performance of vehicles are determined by the comprehensive NRMM but are not within the scope of this manual.

Usually, high-ground-pressure vehicles can travel only a few passes before they break through and become immobilized. Wheeled vehicles usually cannot travel on most of these organic-soil areas. Cone indices denote the relative strength of organic soils. However, the soil-strength vehicle performance relations for organic soils are not as

## Application Of Trafficability Procedures In Fine-Grained Soils And Remoldable Sands

The procedures presented in earlier sections the soil to withstand 1 or 50 passes of the of this chapter are intended for use in tactisame vehicle (or vehicles with smaller
cal operations.

Criteria have been estabor         operating at a slow speed in the lished so that when a given area's RCI is same ruts (in the case of 50 passes) and to equal to or higher than the VCI for 1 or 50
permit stopping and resumption of movepasses                of the selected vehiment, if necessary.

cle, sufficient strength will be available in

## Self-Propelled, Tracked Vehicles And All-Wheel-Drive Vehicles Negotiating Slopes

Solution:

RCI = 100 X 0.85 = 85 RCI. = RCI -                    = 85-58 = 27
Using Figure 7-7, the maximum slope equals 50 percent.

The maximum slope the M1A1 can negotiate under the given conditions is 50 percent.

Example:
The maximum slope negotiable and the maximum towing force or gross vehicle weight for the RCI are essentially equal.

Therefore, when the RCI is known, the maximum slope negotiable by a given vehicle for
50 passes (or by 50 similar vehicles in straight- line formation) can be estimated from Figure 7-7, page 7-12. The differences in the properties of various soils produce some differences in vehicle performance, so NRMM actually predicts performance in finegrained soils based on specific soil type.

## Example:

Estimate the maximum slope an M923
5-ton cargo truck can climb for 50 passes where the slope consists of a remoldable sand whose CI is 93 and RI is 1.00 in the critical layer.

Solution:
Estimate the maximum slope an M1A1 tank can climb for 50 passes where the slope consists of a fine-gralned soil with a CI of 100
and an RI of 0.85 in the critical layers.

RC = 93 x 1.00 = 93        =  RCI -          = 93 - 68 = 25

## Example:

In Figure 7-7, at        =  25, the maximum slope is 35 percent.

The maximum slope the M923 truck can climb under the stated conditions is 35 percent.

Estimate if an M1A1 tank can complete one pass on a level, fine-grained soil with a CI
of 50 and an RI of 0.70 in the critical layer.

(Use Appendix D to determine the VCI.)

## One-Pass Performance

Solution:
The following information is used to determine if various vehicles can make a single pass over different types of terrain:
Self-Propelled, Tracked Vehicles and All- Wheel-Drive Vehicles on Level Terrain The ability of a given vehicle to make one pass on a straight line on level terrain is assured if the RCI of the area is greater than the VCI for one pass       The      of most military vehicles are listed in Appendix D.

Because the RCI is greater than the
(35 is greater than 25), the M1A1 tank can complete one pass.

Immobilization of a vehicle probably will occur when the RCI is less than the      Immobilization may occur even when the RCI is slightly greater than the           if water on the soil surface causes excessive sinkage or slipperiness.

Solution:

## Self-Propelled, Tracked Vehicles And All- Wheel-Drive Vehicles Up Slopes

Using Figure 7-8, at         = 60, the maximum slope = 63 percent. Under the stated conditions, the maximum slope the M1Al tank can negotiate is 63 percent.

The maximum slope negotiable and the max.

imum towing force (as a percentage of gross vehicle weight) for the same       are essentially equal.

Therefore, when the RCI is known, the maximum slope negotiable by a given vehicle for one pass in a straight line up a slope can be determined by using the information in Figure 7-8.

Example:

## Example:

a Determine the maximum slope an M923
truck can climb on one pass where the slope consists of a remoldable sand with CI of 93 and an RI of 0.40 in the critical layer.

Determine the maximum slope an M1A1
tank can climb on one pass where the slope consists of fine-grained soil with a CI of
100 and an RI of 0.85 in the critical layer.

Solution:
When the RC1 is known, the ability of one vehicle to tow another can be determined.

In Figure 7-8, page 7-13, at         = 7, the maximum slope = 21 percent. Under the stated conditions, the M923 truck can climb a slope less than or equal to 21 percent.

## Vehicles Towing Trailers On Level Terrain And Up Slopes

The determination of VCI for towed tractors and self-propelled vehicles with nonpowered wheels requires calculations on an axle-byaxle basis and is beyond the scope of this manual; therefore, in examples involving vehicles towing other vehicles always refer to the towed vehicles as "inoperable, powered vehicles."
The following paragraphs give examples of the application of vehicle performance criteria for both 1 and
50 passes, using Appendix D and Figures 7- 7 through 7-10, pages 7-12 through 7-17:
One-pass performance of vehicles towing trailers is predicted using the comprehensive NRMM and is beyond the scope of this manual. The prediction system is not as well validated as that for single, selfpropelled vehicles. Although the procedure for determining the       for combinations of trucks or tractor-trailers is not discussed, the       of commonly used combination vehicles are listed in Appendix D.

## Vehicles Towing Other Vehicles On Level Terrain

Procedures used in the examples should not be extended to the development of a single VCI for a tractor-trailer combination vehicle. Such development can be reliably made only through the integration of complex considerations which are beyond the scope of this manual. However, some commonly used truck-trailer combination vehicles are listed in Appendix D, where their VCIs are used in the same way the VCIs for other vehicles are used to predict their performance on level terrain.

Example:
Estimate if an M1A1 tank can tow an M923, 5-ton cargo truck for 50 passes on a level, fine-grained soil where the CI is 100 and the RI is 0.80 in the critical layer for the tank, and the CI is 60 and the RI is 0.80 in the critical layer for the truck.

When the RCI is equal to the VCI, the soil has just enough shear strength for the vehicle to overcome its motion resistance.

If the vehicle must tow another vehicle, additional shear strength is required to produce the thrust needed to overcome the motion resistance (or required towing force)
of the towed vehicle. Thus, RCI - VCI, or is a measure of additional shear strength that allows the vehicle to develop a towing force.

Solution:
From Appendix D:

For the M1A1 tank
For the M923 truck RCI for the tank = 100 x 0.80 = 80 RCI for the truck = 60 x 0.80 = 48

Curves that predict the maximum towing force that can be developed by three types of self-propelled vehicles on level terrain are presented in Figure 7-7, page 7-12. The maximum towing force (expressed as a percentage of vehicle gross weight) is related to
      Curves that predict the force required to tow vehicles of various weights and types on level terrain are shown in Figure 7-8, where required towing force (expressed as a percentage of vehicle gross weight) is related to RCI. When a vehicle is required to develop a given towing force, the necessary RCI can be determined.

Vehicles Towing Other Vehicles Up Slopes The maximum slope a vehicle towing another vehicle can negotiate is estimated using the following formula:
The maximum towing force (T1) of the tank is read from the curve in Figure 7-7, page 7-
12, labeled "Tracked vehicles with grousers less than 1 1 /2 inches. "
Using this curve, where the         = 80 - 58 = 22, it is estimated that the tank can tow 25 percent of its weight. Thus, 25 percent of 125.000 =
0.25 x 125.000 = 31.250 lb.

Where
T1 = the maximum towing force (in lb) of the towing vehicle T2 = the force (in lb) required to tow the towed vehicle on level terrain W1 = weight (in lb) of the towing vehicle The required towing force (T2) of the M923
truck is read from the curve in Figure 7-8, page 7-13, for 30,000 lb for wheeled vehicles. On this curve, at RCI = 48, T2 =
49 percent of 32,500 = 0.49 x 32,500 =
15,925 lb, W2 = weight (in lb) of the towed vehicle NOTE: This formula does not apply to slippery surfaces.

Example:
Because the available towing force (31,250
lb) of the M1A1 tank is greater than the required towing force (15,925 lb) for the M923 truck, the tank can tow the truck under the stated conditions.

Example:
Estimate the maximum slope that can be negotiated by an M1A1 tank towing an M923 truck for 50 passes, where the slope consists of fine -grained soil whose shear strength is such that the CI is 100 and the RI is 0.85 in the critical layer for the tank, and the CI is 80 and the RI is 0.80 in the critical layer for the truck.

Estimate if an M923, 5-ton cargo truck can tow an M1A1 tank for 50 passes on a level, fine-grained soil whose shear strength (CI = 95 and RI = 1.00) is the same for the critical layers for both vehicles. The vehicles are the same as those in the previous example.

Solution:
Solution:

RCI = 95X 1,00=95          = 95 - 68 = 27 for the M923 truck
Using Figure 7-7, the maximum towing force (Tl) of the MlA1 tank at        = 27 is 45 percent of 125,000 = 56,250 lb.

The maximum towing force (Tl1 of the M923 truck is read from the curve labeled
"Wheeled vehicles" in Figure 7-7. On this curve,         = 27, T1 = 37 percent of 32,500
= 0.37 x 32,500 = 12,025 lb.

In Figure 7-9, page 7-16, the required towing force (T2) of the M923 truck at RCI = 64 is 38 percent of 32,500 = 0.38 x 32,500 = 12,350 lb.

The required towing force (T2) of the M1A1
tank is read from the curve in Figure 7-8
that is labeled "75,000 lb" for tracked vehicles. On this curve, at RCI = 95, T2 =
18 percent of 125,000 lb = 0.18 x 125,000
= 22,500 lb.

Because the available towing force (12,025
lb) of the M923 truck is less than the required towing force (22,500 lb) of the M1A1
tank, the truck cannot tow the tank.

Thus, the maximum slope negotiable by the Solution:
M1A1 tank towing the M923 truck under the given conditions is 28 percent.

Example:
Using Figure 7-7, page 7-12, where the is 52, the maximum towing force (T1)
for the truck is 47 percent, 0.47 x 32,500 =
15,275 lb.

vehicle with Estimate the maximum slope negotiable by an M923, 5-ton cargo truck towing an M998 high mobility, multipurpose wheeled vehicle (HMMWV) for 50 passes, where the slope consists of fine-grained soil with a CI
of 120 and an RI of 1.00 in the critical layer.

The M998 is a wheeled a gross weight of 7,500 lb.

## 7-16 Soils Trafficability

Using Figure 7-9, the required towing force
(T2) of the M998 at RCI = 120 is 13 percent of 7,500 = 0.13 x 7,500 = 975 lb.

vehicle to overcome its motion resistance.

If the vehicle is required to tow another vehicle, additional shear strength is required to produce the necessary thrust to overcome the motion resistance (or required towing force) of the towed vehicle. Thus, which is the additional shear strength that allows a vehicle to develop a towing force when required (for one pass).

Thus, the maximum slope negotiable by the M923 truck towing an M998 HMMWV
under the given conditions is 36 percent.

Vehicles Towing Inoperable, Powered Vehicles on Level Terrain [One Pass]
Two performance curves, one for selfpropelled, tracked vehicles and one for selfpropelled, wheeled vehicles, are shown in
, When the RCI is equal to the               the soil Figure 7-8, page 7-13. The maximum has enough shear strength for a given towing force (expressed as a percentage of the vehicle's gross weight) that can be For the M923 truck,        = RCI -        =
95 - 30 = 65. In Figure 7-8, page 7-13, at = 65 the towing force (T1) = 54.6 percent of 32,500 = 0.546 x 32,500 = 17,745 lb.

For the M1A1 tank,      = RCI -     = 95 - 25 = 70. In Figure 7-10, at RCIX = 70
the required towing force (T2) = 8 percent of
125,000 = 0.08 X 125,000 = 10,000 lb.

developed by a vehicle on level terrain is related to        The performance curve for all vehicles when towed on level terrain is shown in Figure 7-10, page 7-17, where the required towing force (expressed as a percentage of the vehicle's gross weight) is related to       When the RCI is known, the ability of one vehicle to tow another can be estimated, Example:
Because the available towing force of the truck (17,745 lb) exceeds the force ( 10,000 lb) required to tow the tank, the truck can tow the tank under the stated conditions.

Vehicles Towing Inoperable, Powered Vehicles Up Slopes Estimate if an M1A1 tank can tow an M923, 5-ton cargo truck for one pass on level, finegrained soil whose shear strength is such that the CI is 100 and the RI is 0.70 in the critical layer for the tank, and the CI is 50 and the RI is 0.70 in the critical layer for the truck.

Solution:
The maximum slope a vehicle towing an inoperable, powered vehicle can climb is estimated using the following formula:
Where
For the M1A1 tank,       = 25, gross weight = 125,000 lb, and grousers are less than 1 1 /2 inches. For the M923
truck,       = 30 and gross weight = 32,500
lb. (See Appendix D.)

**T1 = the maximum towing force (in Ib) of the towing vehicle**
T2 = the force (in lb) required to tow the inoperable, powered vehicle on level terrain W1 = weight (in lb) of the towing vehicle W2 = weights (in lb) of the towed vehicles For the M1A1 tank, RCI = 100 x 0.70 = 70
and      = 70 - 25 = 45. In Figure 7-9, page 7-16, at        = 45, the maximum towing force (T1) = 63 percent of 125,000 = 0.63 X 125,000 = 78,750 lb.

NOTE: The relation does not apply to slippery surfaces.

Example:
For the M923 truck, RCI = 50 x 0.70 = 35
and      = 35 - 30 = 5. In Figure 7-10, at
      = 5, the required towing force (T2) =
25 percent of 32,500 = 0.25 x 32,500 =
8,125 lb.

Because the available towing force (78,750
lb] of the tank exceeds the required towing force (8,125 lb) of the truck, the tank can tow the truck under the stated conditions.

Estimate the maximum slope that can be negotiated by an M1A1 tank towing an M923 truck on one pass, where the slope consists of fine-grained soil with a CI of 100
and an RI of 0.85 in the critical layer for each vehicle

## Example:

Solution:

RCI = 100 X 0.85 = 85
Estimate if an M923, 5-ton cargo truck can tow an M1A1 tank for one pass on level, fine-grained soil whose CI is 95 and RI is
1.00 in the critical layer for each vehicle. Solution:
For the M1A1 tank,        = RC1 -       = 85 - 25 = 60. In Figure 7-8, at          = 60
the maximum towing force (T1) = 63 percent of 125,000 = 0.63 x 125,000 = 78,750 lb.

itified by its standard nomenclature. Appendix D also includes performance categories for each vehicle and each vehicle's VCI for
1- and 50-pass performance.

For the M923 truck,               = RCI - 85 - 30 = 55, In Figure 7-10, page 7-17, at = 55, the required towing force (T2). 8.3 percent of 32,500 = 0.083 x 32,500.

2,698 lb.

## Performance Categories

Thus, the maximum slope negotiable by the M1A1 tank towing the M923 truck under the given conditions is 48 percent.

Military vehicles can be divided into seven arbitrary categories according to the minimum CI requirements The range of               and               for each category (exceptions are numerous) are shown in Table 7-3.

## Classes Of Vehicles

Determination of VCIs for New or Unlisted Vehicles For conventional-type vehicles not shown in Appendix D, the following procedure can be used to calculate the VCI: First, a mobility index (MI) is calculated for each vehicle.

Appendix D contains a list of vehicles divided into four classes: self-propelled, tracked vehicles; self-propelled, wheeled vehicles: construction equipment; and trucktrailer combinations. Each vehicle is iden-
Although the NRMM calculates actual VCIs based on an axle-by-axle basis, the VCI can be estimated by using the following steps to calculate the MI and VCI for each type of vehicle, assuming equal wheel or track loads and all wheel drive:
(The NRMM adjusts for uneven loads and differences in tire pressures.

With the newer trucks the        may vary 20% with tire pressure changes ONLY.)
NOTE: These formulas could be used to determine estimates of VCI and adjusted by
20% to reflect that drivers of trucks with central tire inflation will reduce as required.

Self-Propelled, Tracked Vehicles.

Step 1. Determine the MI.

Step 2. Use Figure 7-11 to convert the MI to VCI.

[For MIs above 40, the        can be obtained from the equation           = 25.2 + (0.454 x MI).]
Self-Propelled, Wheeled Vehicles.

(1) All-wheel-drive vehicles.
Step 1. Determine the MI.
Step 2. Enter Figure 7-11, page 7-21, to convert the MI to VCI. [For MIs above 40, the
       can be obtained from the equation         = 25.2 + (0.454 x MI)].

(2) Rear-wheel drive vehicles only.

If the vehicle being considered is not equipped with an all-wheel drive, the MI is computed according to the formula for all-wheel-drive vehicles, then multiplied by 1.4 to obtain the VCI. (3) Half-tracked vehicles. The all-wheel-drive formula is used to obtain the VCI of halftracked vehicles by assuming that the vehicle has wheels instead of tracks on the rear end.

The wheels are assumed to be of the same size and have the same load as the front wheels, A grouser factor of 1.1 is used
(to account for increased traction provided by the rear tracks).

## Towed, Tracked Vehicles.

Step 1. Determine the MI.

Step 2. Use Table 7-4, page 7-24, to convert the MI to VCI. [For MIs above 40, the VCI can be obtained from the equation VCI50 = 25.2 + (0.454 x MI)].

Towed. Wheeled Vehicles, Step 1. Determine the MI.

clearance = clearance in inches Step 2. Use Table 7-5, page 7-25, to convert the MI to VCI.

[For MIs above 40, the VCI50
can be obtained from the equation VCI50 = 25.2 + (0.454 x MI)].

Limitations. MIs and resultant VCIs from determination of probable RCI that will pertrailers (towed, tracked and towed, and mit a trailer to complete 25 to 40 passes wheeled vehicles) may be used only for without the axle or undercarriage dragging.

NOTE: For Mls above 180, the VCI is obtained from the following equatlons:
(1 Pass) VCI1 = 11.48 + 0.2 Ml - {39.2/(Ml + 3.74)}
(50 Passes) VCI50 = 28.23 + .43 Ml - {92.67/(Ml + 3.67)}
NOTE: For Mls above 160, the VCI is obtained from the followlng equations:
(1 Pass) VCI1 = 11.48 + 0.2 Ml - {39.2/(Ml + 3.74)}
(50 Passes) VCI50 = 28.23 + .43 Ml - {92.67/(Ml + 3.67)}

## Operation In Coarse-Grained Soils

Coarse-grained soils present trafficability problems different from those encountered in fine-grained soils. Some important differences are
date has not permitted development of CI performance relations for tracked vehicles because all tracked vehicles have been able to travel on all level, coarse-grained soils encountered. Furthermore, the effects of soil strength on the performance of a given tracked vehicle are minimal.

- Coarse-grained soils do not respond to
the remolding test (except for highly
saturated sands).
One-pass performance of all-wheel-drive vehicles has been determined. In most cases, the first pass is the most critical, and subsequent passes are assured if the first pass is successful,

- Wheeled-vehicle performance is affected
more by tire-inflation-pressure changes
on coarse-grained soils than on finegrained soils.

## All-Wheel-Drive Vehicles On Level Terrain

- Level, coarse-grained soils seldom cause
immobilization of tracked vehicles or allwheel-drive wheeled vehicles when operating at low tire-inflation pressures.
- The first pass over a coarse-grained soil
area is the most critical, and subsequent passes are usually assured if
they are made in the first-pass ruts.
Coarse-grained soil in the dry state is easily recognizable. It is the round, granular material found on most beaches and in sand dunes. When wet, however, it may be confused with remoldable sand or even finegrained soil. Because coarse-grained soils do not remold there is no need to conduct the remolding test. Use RCI for finegrained soils and CI for coarse-grained soils
(assume RI = 1.0.)
The ability of a given vehicle to travel one pass in a straight line over level terrain is generally assured if the CI of the area is greater than the VCI. The prediction of the performance of a wheeled vehicle in sands is a complex interplay among many vehicle characteristics including tire size, tire pressure, the number of tires, tire construction, vehicle characteristics, and the soil condition (in terms of soil strength and moisture content). Since most natural, sandy soils contain fine-grained materials that cause the soil to behave like a fine-grained soil, only dry-to-moist, poorly-graded sands (SP)
are evaluated using coarse-grained vehicle performance relationships in NRMM or CAMMS.

Use the following procedure to ensure the soil in question is coarse-grained: Push the penetrometer into the soil. If the color of the soil near the penetrometer immediately becomes lighter, the internal drainage is good, which signifies a coarse-grained soil, Another test is to confine a soil sample in the remolding cylinder and attempt to penetrate it with the cone penetrometer. If the soil is coarse-grained, it will be difficult or impossible to penetrate.

Other sandy soils with appreciable quantities of fine material (SM, SC, SM-SC) are treated in the NRMM as fine-grained soils.

The need to evaluate the interplay among terrain and vehicle characteristics requires that the coarse-grained soil predictive relationships be computerized into the NRMM. Therefore, these relationships cannot be simplified to a point where they could be displayed as figures in this chapter. The relationships do follow the trends of the fine-grained relationships, and they compute a minimum soil strength requirement for traffic    based on measured CI (RI is considered 1.0 or greater for these The presence of vegetation in coarse-grainedsoil areas indicates the soil is stabilized and is of high trafficability. This effect is reflected in high CI readings. Testing to

## 7-26 Soils Trafficability

derized, found on most bulldozer-type vehicles.

soils). Speed predictions can then be made for these areas.

Vehicles with girderized tracks generally produce higher tractive forces on SP soils than do flexible-tracked vehicles.

## Calculations Of Vehicle Cone Index

In coarse-grained soils, the performance of wheeled vehicles is generally affected most by tire pressure. To optimize vehicle performance, tire pressures should be reduced to mud, sand, and snow pressure, at a minimum, or to the emergency tire pressures if speed is not a requirement. In this manner, vehicle ground pressure is decreased from on-road, and vehicle traction is maximized for the terrain conditions encountered.

## Tracked Vehicles On Level Terrain

As a general rule, tracked vehicles are able to travel on all level, coarse-grained soils regardless of soil strength. Performance predictions in the NRMM are made for two categories of tracked vehicles; flexible, found on most military vehicles, or gir-
Calculation of a coarse-grained VCI for a vehicle configuration is considered beyond the scope of this manual. These predictions are made using the comprehensive NRMM. In general, wheeled vehicles operating in sands should use the lowest tire pressures possible and all-wheel-drive for maximum off-road performance. The user should be aware that immobilization can easily occur in these soils, especially if the soils are dry and loose, and should prepare for such emergencies. Tracked vehicles generally do not suffer immobilization on level SP soils.

## Trafficability Data

geologic maps; aerial photos; or interrogation.

The accuracy of the trafficability estimate depends on the type, quantity, and accuracy of the available data. The analyst's ability to interpret the data is also important, especially if soil types must be deduced from geological maps and air photos.

The objective of mapping trafficability data is to provide commanding officers with an estimate of an area's trafficability prior to actual operation.

The estimate consists of placing symbols that describe the trafficability of a small area at strategic points on existing maps as shown in Figure 7-12, page 7-28. The maps produced by the techniques described in the following paragraphs are elementary compared with the complicated and comprehensive maps now in production for use with the NRMM.

## Weather Conditions Estimating

For estimating trafficability, consider only two general weather conditionsthe "dry season" and the "wet season."
Trafficability can be estimated if weather conditions, soils, and area topography are generally known.

Weather and climatic information usually are available, even for remote areas, from meteorological records, climatology textbooks, or personnel interrogation. Soils and topography data may be obtained from topographic, soils, and Dry Season. A dry season is defined as a time when climatic and vegetation factors combine to produce, in general, low soil moistures.

For temperate, humid climates, such as the United States east of the Mississippi River, the dry season is from about the first of May to the first of November. In this season, evaporation of water from the and embankments can also be obtained from aerial photos.

soil is high because of long days, high temperatures, and few clouds, and water is rapidly extracted from the soil and transpired to the atmosphere by growing plants. A dry season may also occur at other times of the year as a result of long periods of fair weather. Areas of arid climates may be considered to be constantly in a dry season.

The techniques for identifying soils from aerial photos are so complex that only welltrained personnel can fully use aerial photos for this purpose. However, some general information can be obtained by personnel with a minimum of training. For example, orchards are usually planted in welldrained, sandy soils; vertical cuts are evidence of deep loessial (silty) soils; and tile drains in agricultural areas indicate the presence of poorly drained soils (probably silts and clays).

During the dry season, fine-grained soils and remoldable sands of any type usually are trafficable and, in general, are of higher trafficability than dry, coarse-grained soils.

The trafficability of dry, coarse-grained soils is poorer than that of all wet, coarsegrained soils except quicksand. Even in the dry season, trafficability of any type of soils is affected by a high water table that results from underground springs, low-lying and poorly drained soils, or any other cause.

In a given photo, light color tones generally indicate higher elevations, sandier soils, and lower soil moisture than those signified by dark color tones. However, the same color tone may not signify the same conditions in the same photo and may signify an entirely different condition in another aerial photo. In addition, natural soil tones may be obscured and modified by tones created by vegetation (natural and cultivated), plowed fields, and cloud shadows.

Geologic Maps.

Geologic maps show parent material and age data. With that information and a general knowledge of climate, topography, and vegetation, trained analysts can estimate the soil types likely to be found in the area.

Wet Season. A wet season is defined as a time in which weather conditions combine to produce high soil moistures. In temperate, humid climates, the wet season extends from about the first of November to the first of May. During the wet season, frequent rains, low temperatures, heavy cloud cover, and the absence of growing plants tend to keep soil moisture near a maximum value.

Melting of snow and thawing of previously frozen soils may also produce wet soil conditions. Wet seasons may occur at any time as a result of prolonged rains, floods, or irrigation.

Adding moisture to a soil affects the strength of that soil; the effect differs with soil types.

## Topography And Classification Of Soils

The configuration of the soil surface and soil types in a given area are determined from the sources that follow.

Soils Maps. Trafficability can be estimated rapidly from maps that delineate surface soils according to the USCS, although these maps are scarce. The more common types of soils maps are those using an agricultural system of soil classification. In formation from agricultural maps must be translated into engineering terms before a trafficability estimate can be made. No exact method exists for doing this, but analysts familiar with the classification systems can usually make good translations. For example, the term "loam" in the agricultural classification system usually includes CL and ML soils in the USCS.

Aerial Photos.

Elevations and slopes can be estimated by personnel who are properly instructed to read (with the aid of stereopairs)
and interpret information in aerial photos. Accurate elevations and slopes can be obtained with mechanical equipment by operators trained to use such equipment.

Locations of rivers, forests, escarpments, Topographic Maps.

Physical features such as rivers, streams, cultivation, forests, and to precisely plan the optimum route for the configuration.

roads can usually be identified from a topographic map. Estimates of surface slopes can be made from the contour lines (lines passing through points of equal elevation).

Cross-country traverse or route movements can be configured to show the additive effects on vehicle speeds of mined areas, obstacles emplaced, choke points, or gap crossings, together with changes in vehicle configurations which may result as a consequence of offensive or defensive actions during tactical or combat operations. The models may also be used by materiel and hardware developers to determine the effects of proposed designs or changes on manual vehicle performances. Thus, the uses and displays achievable through the NRMM or CAMMS computer models are basically limited only by the imagination or requirements of the user.

For trafficability classification purposes, topography has been divided into two classes: low topography and high topography, Low-topography areas are those at comparatively low elevations with respect to surrounding terrain, and high-topography areas are those at comparatively high elevations.

Absolute elevation has no significance in identifying the topography class.

Low-topography areas are usually poorly drained and have water tables occurring within 4 feet of the surface at some time during the year. High-topography areas are usually medium-well to welldrained and do not have water tables within 4 feet of the surface at any time during the year.

## Trafficability Maps

A wide variety of mobility-related products can be obtained from computerized mobility models such as the NRMM or CAMMS. Input terrain data includes land use: terrain slope; obstacles; soil types; vegetation type, density, and spacing; surface geometry; linear and hydrologic feature data; and road and trail data. This data is used by the models with input vehicle data to make speed or GO/NO GO predictions for each individual terrain unit (on a quad sheet) formed by the complex interplay of the input variables. Visual displays or hard copies of the video displays can be used for such tasks as vehicle and terrain analysis, operational planning, route selection, convoy planning, or unit-movement preparation.

As an example of hard-copy outputs from the mobility models, three graphical products are presented in Figures 7-13
through 7-15, pages 7-31 through 7-33, as they would appear on the console of a CAMMS computer. Figure 7-13 depicts the cross-country speed performance of a US
Army M1A1 tank in Germany. The different cross-hatched areas are used to depict cross-country mobility rates of 0-10,
10-20, 20-30, and greater than 30
kilometers per hour (kph) for the tank. The shading and the speed increments are arbitrary.

The initial assessment of the display in Figure 7-13 would indicate the platoon can move across this quad at greater than 30 kph except for scattered areas where speeds will drop to 20-30 kph.

River and stream crossings will be required in west-east movement across the quad, and these crossings will require 30 minutes except for a few crossing points which would require "zoom"' techniques to locate.

Scattered NO GO areas should be avoided, especially those concentrated in the upper portion of the quad. On-road mobility in most areas should exceed 10 kph, Figure 7-14 is a display of potential landing zones from CAMMS for the same areas as in Figure 7-13. The potential landing-zone map indicates primarily unfavorable landingzone sites, with favorable sites located in the northwest third and southeast corner of Comparison visual products can also be obtained to show quad-sheet-sized differences in the mobility performance levels of red or blue vehicles to contrast the performances of a vehicle in a variety of configurations, such as with different tire pressures, with and without towed loads, or with different load configurations.

The derived displays can then be enlarged via "zoom" techniques

## 7-30 Soils Trafficability

Example: In the fraction the quad. This display helps guide the user to the most suitable sites for landingzone construction.

B is the soil type condition (from Table
7-5, page 7-25), 80 is the RCI, 25 is a 25-
percent slope, and S is a slippery surface. Solution:
Figure 7-15, page 7-33, is a display of USCS soil-type descriptions from CAMMS
for the same area as in Figures 7-13 and 7-
14, pages 7-31 and 32. This display indicates the locality of soil types that may be useful in scouting for construction materials or sites more suitable for road and airfield construction. Thus, the mobility analysis is now a very powerful tool for the military planner. It integrates natural features of the landscape with vehicle parameters to produce mobility products which can be used by materiel developers, planners, war garners, or combat soldiers in the field to plan real-time red and blue actions in terrains around the world.

To interpret the meaning of B - 8 0
25 - S, first find in Figure 7-7, page 7-12, the for the three vehicle types on 25-percent slopes. For wheeled vehicles,   = 17; for conventional, tracked vehicles,   = 13;
and for long-grousered, tracked vehicles,
= 11. Then, for each type of vehicle, find the     . Thus, the area is trafficable for wheeled vehicles with     less than
63         = RCI -       or        = 80-17), for conventional, tracked vehicles with less than 67, and for long-grousered, tracked vehicles with     less than 69.

## Manually Mapping Soil Conditions And Trafficability

Since the slope may be slippery, the operations officer should order all wheeled vehicles to be equipped with traction devices and should expect some sliding and steering difficulty.

The photomap in Figure
7-12 shows how areas can be delineated in this manner. Example:
Although mapping soil conditions and trafficability through manual means is rarely done since the development of computerized mobility models, it is important that the procedure be presented should the need ever arise. The following paragraphs describe the proper procedure in detail:
Fifty M60 tanks (102,000 lb) and 50 M923
trucks (32,500 lb) are to be moved from point X to point Y in the area shown in Figure 7-12.

Movement must be cross-country because the roadnet is heavily mined. Solution:
VCIs vary widely, and it is desirable to present basic terrain data that can be compared directly with VCIs. The four basic terms describing trafficability are: soil type, RCI, slope, and slipperiness.

## Step 1, From Appendix D:

Vehicle
Tank
20
48
Truck
30
68

The soil-type condition is shown by A, B, C, or D (as defined in Table 7-6); RCI is shown by a single number; slope, in percent, is shown by a single number; and slipperiness is shown by N, P, or S. (Stickiness effects are not considered significant enough to include on maps.) The four factors may be presented (as in Figure 7-12, page 7-28) in fractional form with two items in the numerator and two in the denominator.

Step 2. Examine the possibility of singlefile travel through flat terrain. All vehicles can negotiate areas 1 and 6. The RCI of 50
for area 3 will allow passage of all 50 tanks but not all 50 trucks. The tanks can proceed in single file from X through areas
1, 3, and 6, consecutively to Y. However,

## 7-34 Soils Trafficability

through areas 1, 5, and 6, respectively, provided caution is used with the trucks.

This route is shown as a dashed line.

the trucks will have to fan out and use more lanes with less than 50 vehicles in single file to ensure passage through area 3
(    to 30, RCI less than 50). The slipperiness of area 3 may present an insurmountable problem for the trucks unless traction devices are available.

This example indicates the usefulness of mapped trafficability data in planning operational exercises.

An alternative route that would be safe for all vehicles would be through areas 1, 5, and 6, consecutively, provided the slope of area 5 can be negotiated. For this example, it is assumed that the combination of 60-percent slope and other terrain obstacles in areas 2 and 4 would not allow travel through them.

The presentation of trafficability data for strategic purposes is most effective when one vehicle is used as a standard, reference vehicle. For example, if the vehicle selected has a VCI of 49 and the information on that specific vehicle is presented, trafficability data for that vehicle can be generalized and considered applicable to all vehicles with a VCI of 49 or less.

Recommended techniques of mapping trafficability data follow:
Step 3. Check the slope-climbing ability
(using Figure 7-7 and Figure 7-8, pages 7-
12 and 7- 13) of both vehicle types in area
5:

## 1 Pass Vehicle Slope

| Tank            | 30%            |
|-----------------|----------------|
| 6 + 2 0  =  2 6 |                |
| Truck           | 30% 11 11 + 30 |
| =               | 41             |

## 50 Passes Vehicle Slope

 - The base of the map should be a standard topographic map printed in a gray monochrome with streams in a strong blue color.
 - The four soil-slope combinations should
be shown as trafficability symbols, as indicated in Table 7-7. (See previous weather conditions.)
 - Obstacles should be indicated by red
added numbers circled in red.

|         | T a n k   | 30%     |
|---------|-----------|---------|
| 15      | 15        | +       |
| 48 = 63 |           |         |
| Truck   | 30% 20    |         |
| 20      | +         | 68 = 88 |

 - Forests should be indicated by appropriate open-type patterns in strong
green.
 Z The reverse of the trafficability map
should contain an inset map of the principle physiographic provinces,
landforms, geologic areas, and related
data used in making the analysis. The
inset map should show in detail all important data on soils, topography, and
obstacles that cannot readily be shown on the face of the map.
The tanks can negotiate the 30-percent slope in single file (available RCI of 80 is greater than the required RCI of 63). All trucks cannot negotiate the slope in single file (available RCI of 80 is less than the required RCI of 88), but they can fan out and negotiate the slope on a one-pass basis (available RCI of 80 is greater than the required RCI of 41).

The conclusion is that all vehicles could travel from X to Y

## Soil-Trafficability Classification

Soil classification of a specific area can be raphy (high or low) has been identified, and accomplished rapidly for seasonal (highthe VCI for vehicle category has been moisture) conditions when the soil has been determined (from Table 7-3, page 7-19, or classified in terms of the USCS, the topog-
Appendix D) or computed, when necessary, as previously described.

## 7-36 Soils Trafficability Fine-Grained Soils

greater than 75 percent, but less than 90 percent, of traversing the area.

The trafficability classification of finegrained soils is shown in Table 7-8, page
7-38.

 - Vehicles with a         or        less than
18 will have a probability equal to or
greater than 90 percent, but no more
than 100 percent, of traversing the area.

## Coarse-Grained Soils

The interpretation of the example shown in the "Low Topography, High Moisture Condition" graph of Table 7-8 for a level area of MH soil follows:

- Vehicles with a         or      equal to
or greater than 84 will have a less than
50 percent probability of traversing the
area.
- Vehicles with a       or      equal to
or greater than 56, but less than 84,
will have a probability equal to or
greater than 50 percent, but less than 5
percent, of traversing the area.
The trafficability classification of coarsegrained soils can be obtained from Figure
7-16, page 7-39.

The classification interpretation is the same as for the trafficability of fine-grained soils from Table
7-8. To use Figure 7-16, identify only the coarse-graincd soils (location and origin)
and determine the VCIs from the equation presented earlier in this chapter. Figure 7-16 applies to wheeled vehicles only. The effect of the strength of coarse-graincd soils on tracked-vehicle performance is negligible.

- Vehicles with a       or     equal to
or greater than 18, but less than 56,
will have a probability equal to or

nance, Repair, and Rehabilitation of Roads, Airfields, and Heliports
                                         Maintenance and Repair Considerations Maintenance and Repair Operations
                                                                                                                                   Road Maintenance
                                                                                                                                                          Airfield and Heliport Maintenance

## Maintenance, Repair, And Rehabilitation Of Roads, Airfields, And Hellports

Maintenance is the routine prevention and correction of normal
damage and deterioration (from use and the elements) to keep
road and airfield surfaces and facilities in usable condition.
Repair is that work necessary (other than maintenance) to correct
damage caused by abnormal use, accidents, hostile forces, and
severe weather. Repair includes the resurfacing of a road or
runway when maintenance can no longer accomplish its purpose.
Based on this manual, rehabilitation is the restoration of cap-
tured airfields and heliports to usable condition. Rehabilitation
resembles war-damage repair except that it is accomplished
before occupancy.

## Maintenance And Repair Considerations

periods of reduced activity. Reopen the facility as soon as practicable.

The purpose of all maintenance and repair activities is to keep roads, airfields, or other installation surfaces in as usable and as safe a condition as the situation permits. Prompt and adequate maintenance is important. Once surface deterioration or destruction has started, it can proceed very rapidly. Postponing minor maintenance jobs can result in the development of major repair jobs involving the subgrade, base course, and surface.

Use the following guidelines when performing maintenance and repair work:

- Remedy the cause before repairing the
problem. For example, surface repairs
made on a defective subgrade are
wasted. All maintenance and repair
jobs should include an investigation to
find the cause of the damage or
deterioration. To ignore the cause is to
invite the prompt reappearance of
damage. Ignore the cause only when
making temporary repairs to meet immediate, minimum needs under combat or other urgent conditions.
- Maintain and repair existing surfaces as
closely as possible to the original construction in strength, appearance, and
texture. Spot strengthening may create
differences in wear and traffic impact
that can harm adjoining surfaces. Also,
uniformity simplifies maintenance and
repair operations.
- Ensure that maintenance and repair activities interfere as little as possible
with the normal flow of traffic. Whenever feasible, plan and perform maintenance and repair activities to permit at least partial use of the facility. When
it is necessary to close the facility to all traffic, select alternative facilities or perform repair work at night or during
essential facilities. One pothole in a heavily used road that is in otherwise excellent condition takes priority over repairs to less heavily used roads in poor condition.

- Prioritize the needed repairs based on
the tactical requirements, the traffic
volume, and the hazards that result
from complete failure of the facility. For
example, roads used for tactical-operations support take priority over less

## Maintenance And Repair Operations Drainage Inspection

Maintenance and repair operations include many tasks besides improving the pavement condition. To ensure a comprehensive maintenance and repair operation, incorporate the following tasks:

 -
Routine inspections.

Material stockpiling.
 - Maintenance and repair of all related
drainage systems.
Ensure that all drainage channels and structures arc unobstructed. Check culverts and drainage lines for structural damage.

Inspect check dams for debris and excessive erosion.

Investigate water ponding on or adjacent to surfaced areas. Inspect the system drainage during or after every storm. Also, thoroughly inspect the system in late fall to prepare for winter and in early spring to ensure minimum spring breakup difficulties. Inspect subsurface drains at least twice a year.

- Maintenance and repair of the actual
pavement, including dust and mud control and snow and ice removal.

## Materials For Maintenance

- Miscellaneous tasks, including the
maintenance and repair of necessary
buildings, structures, and utilities, and
the operation of necessary utilities.

## Maintenance Inspections

The purpose of maintenance inspections is to detect early evidence of defects before actual failure occurs. Frequent inspections and effective follow-up procedures prevent minor defects from becoming major repair jobs. Inspect surface and drainage systems carefully during rainy seasons and spring thaws and after heavy storms.

## Surface Inspection

Generally, materials required in the maintenance and repair of roads and airfields arc the same as those used in new construction.

Open pits and prepare stockpiles of sand and gravel; base material; and premixed, cold patching materials at convenient places and in sufficient quantities for emergencey maintenance and repair. Arrange stockpiles for quick loading and transporting to the road or runway. Build onc of the several types of trap-and-chute combinations described in Chapter 5 of TM
5-332 for sand, gravel, and base materials, Premixed. cold patching material may be prepared as explained in Chapter 9 of TM 5- 337. Maintain small quantities of aggregate in dry storage for concrete patching.

## Drainage Maintenance

Defective or inadequate drainage causes most pavement failures and deterioration.

Pending or delayed runoff of surface water allows seepage into the pavement structure unless the surface is tightly sealed.

Surface defects can usually be attributed to excessive loads, inferior surfacing material, poor subgrade or base conditions, inadequate drainage, or a combination of these conditions. Surface inspections should include a complete inventory of the current pavement defects. Careful investigation of the causes of the defects will allow for timely maintenance to prevent the pavement defects from requiring repair.

## Surface Drainage

Mark areas where pending occurs on sur -
faced areas.

Correct such problems by filling or raising depressions and by providing outlets for water blocked by high shoulders.

Control penetration of storm water through pavement by scaling joints and cracks.

Keep unpaved roads and airfields crowned to prevent water from remaining on the road or airfield where it will saturate and weather the surface.

Maintain crowns and superelevations with graders or drags.

## Shoulders

Keep shoulders smooth and graded so water will drain from the surfaced area toward the ditch.

Replace eroded shoulder material on paved surfaces with new material. Material cleaned out of ditches can often be used 10 rebuild shoulders. Shoulders should be kept bladed flush to, or slightly below, the edges of the pavement and should slope away from the pavement to prevent water seepage into the subgrade.

## Drainage Ditches

Cut-slope interceptor ditches must be considered for all side-hill and through cuts to prevent gully washing and erosion from the top of the cuts. If benching or terracing has been used in the design of the cut, ensure that the top of each bench is sloped back into the cut to provide for proper drainage. Also ensure that each bench top is wide enough to maintain that drainage with earthmoving equipment. A good rule of thumb is to make benches at least as wide as a dozer blade. Figure 8-2, page
8-4, illustrates proper terraced side-hill-cut drainage.

Keep drainage ditches clear of weeds.

brush. sediment. and other debris that obstruct water flow. Maintain ditches as to line and grade.

Correct sags and minor washouts as they occur. Side ditches can usually be maintained with graders.

For proper design considerations of cut slopes, refer to Chapter 10 of FM 5-410.

## Culverts

When cleaning and shaping, avoid unnecessary blading or cutting that destroys natural ground cover. Where possible, develop dense sod to stabilize open ditches.

Where vegetation is not effective because of soil or moisture conditions, erosion may be corrected by lining the ditch with riprap, asphalt-coated membrane, or concrete.

Keep culverts clear of debris and sediment (Figure 8-3, page 8-4). This prevents water from cutting around or undermining the culverts.

Inspect culverts frequently to determine whether they arc func-tioning properly. Cleaning by hand is usually necessary after heavy rains.

## Nonpaved Surfaces

Basic maintenance of nonpaved surfaces includes shaping the cross section to maintain adequate drainage anti a smooth, compacted surface.

Inspect check dams in side ditches and clean them regularly. The weir notch of a check clam must be kept clean or water will cut into the surfaced area at the edge of the dam (Figure 8-1). The aprons of check dams must also be maintained, and paving material must be replaced when washed out. Dikes or berms may be required along the tops of high-fill slopes to prevent gullies and washes.

## Equipment

or washboarding of drag is shown of the surface. One type in Figure 8-4.

## Materials

Most surface maintenance consists of light scraping with grader blades and drags. Multiple-blade drags of iron or iron-shod, heavy timber may be used for normal scraping. Drags are frequently used to float mud and water off a road and to prevent corrugation Materials removed from ditches, other than silt, some clays, and all organic soils (OL, OH, Pt), may be used on shoulders and traveled ways. Dispose of silt deposits when removed; they are not suitable for construction.

After heavy storms and spring thaws, additional material may need to be hauled in.

## Procedures

Keep traffic areas and shoulders free of potholes, ruts, and irregularities. Light blading will prevent corrugation or washboarding.

Work from the ditches to the center of the road to ensure good drainage and proper road crowning. Since loosened, dry material cannot be compacted, blading or dragging should be done during or soon after rains. For prolonged dry spells or when surface material will not compact, add water or moist subsurface material objectionable material and replace it with a more stable material. When adequate repairs cannot be made, soft spots can be temporarily reinforced by adding crushed rock or clean gravel.

Keep non paved surfaces crowned to prevent water from remaining on the surface and saturating the soil.

Maintain the crown and superelevation with drags or graders.

Dust control may be a problem under some conditions.

Spraying with water or a bituminous stabilizer is the most commonly used method of controlling dust. Dust control is discussed further in Chapter 12 of FM 5-430-00-2/AFPAM 32-8013, Vol 2.

Examples of road repairs are shown in Figure 8-5, page 8-6.

## Oiled Surfaces

The routine maintenance of oiled surfaces consists of shaping and patching. Shaping is done with graders or drags. Patching may be done with a mixture of the soil and oil. Oiling is necessary each year because oiled surfaces frequently break up in the spring and become very rough. Thorough scarifying. blading (or dragging), and reshaping is necessary before oiling each year.

## Gravel Surfaces

with a rototiller, plow, or scarifier before compaction.

Maintenance procedures for gravel surfaces are much the same as for nonpaved surfaces. Continual shaping is needed to maintain a smooth surface and a uniform crown, and the drainage system must be kept functioning.

Compaction of the graded surface material will reduce maintenance and repair for nonpaved surfaces. The type of roller used will vary with the material compacted. The correct moisture content will result in the most economical compaction.

## Surface Maintenance

Soft spots, indicated by rutting or shoving of the surface, are generally caused by excess moisture, poor subsurface drainage, or unstable material. Determine the source of excess moisture and correct the drainage.

On traffic areas, cobbles may be used to stabilize small areas of failure. Where surface failures are caused by pockets of mulch or peat, it may be necessary to remove the Heavily-traveled, graveled surfaces require constant attention by maintenance patrols.

Intensive maintenance is required when the surface is first open to travel. Bumps compacted at this time remain in the surface and can be corrected only by scarifying or adding more material. Blade or drag the surface soon after rain until all ruts and holes are filled. Do not work on a dry

## Treatment Of Corrugations

surface. Maintain a crown of at least 1/2
inch per foot. Multiple blade drags or sled drags can be used for routine maintenance, but graders are necessary for heavy reshaping work.

All gravel surfaces tend to develop transverse or nearly transverse waves, called corrugations, which may progress into ruts as deep as 4 inches and from 1 1/2 to 3 feet apart. After this stage, they become major grooves needing extensive repair.

Keep a slight excess of gravel available at the edges of the roadway and blade it uniformly over the surface in wet weather.

Stockpile additional materials in advance of fall and winter and prolonged wet periods. Material added or spread on the surface during warm, dry weather is of little value.

## Repair Of Potholes

Some blade equipment inherently chatters and starts slight irregularities, especially when the operator attempts to move a heavy cut. Corrugations often appear to start from small holes or depressions made when the road is wet or from an obstruction such as a stick or rock. Other contributing factors are a soft subgrade, poor grading of the gravel, poor binder, and an insufficient amount of binder.

Most potholes are caused by material displaced by traffic. Initially they are shallow and are readily filled by blading when the surface is moist.

Deep holes require filling with additional material. New material should be moistened and compacted.

Corrugations can be prevented to a considerable extent by frequent maintenance and by the careful use of maintenance equipment. Once corrugations form, they can be

## Bituminous Surfaces

The maintenance and repair of bituminous surfaces are discussed in Chapter 9 of TM 5-337. Some considerations applicable to bituminous-surfaced traffic areas follow.

removed only by thoroughly scarifying, reshaping, and compacting. Regrading, as this is called, should begin with a thorough cleaning and reshaping of the shoulders and ditches, continuing across the entire roadway.

## Inspection Use Of Calcium Chloride

Maintenance patrols should frequently inspect bituminous pavements for early detection of failures. Small defects quickly develop into large ones, resulting in pavement failure unless promptly corrected. Small crews using hand tools can quickly make minor repairs with a minimum interruption of traffic. Large, bituminous repairs require more time, personnel, and equipment. Such repairs also interfere with traffic. In extreme cases, detours may be required to avoid complete traffic stoppage.

## Patches

Calcium chloride may be applied to a gravel surface to control or eliminate dust, prevent the loss of material under the whipping action of traffic, and aid in maintaining a dense surface. The usual method is to apply 1 pound of calcium chloride per square yard in the late spring and 1/2 pound per square yard twice during the summer season.

However, the amount of rain, the volume of traffic, and the character of the gravel affect the quantities required.

Calcium chloride is corrosive to metal surfaces and may require more maintenance for aircraft and vehicles.

All patches should be trimmed square or oblong with straight, vertical sides running parallel and perpendicular to the centerline of the traffic area, as explained in Chapter 9 of TM 5-337.

## Temporary Repairs

The best time to apply calcium chloride is following a rain and after necessary blading or dragging is completed. If the application cannot be deferred until rain occurs, water the surface before applying the calcium chloride. For best results, apply calcium chloride before the traffic area becomes dry and dusty.

## Processed Material Surfaces

Any stable material may be used for temporary repairs in combat areas or where suitable material is not available and the traffic area must be patched to keep traffic moving, Good-quality soil and masonry, such as concrete rubble, are suitable for this purpose. All such patches must be thoroughly compacted and constantly maintained with replacement material. More permanent patching should be accomplished as soon as possible.

## Maintenance Of Shoulders

Traffic areas composed of processed materials (crushed and screened rock, gravel, or slag) are maintained by methods similar to those used on gravel surfaces.

When coarse, processed materials are used, surface failures are usually in the form of sharp-edged holes caused by poor drainage. Repairs require cleaning the holes down to the solid subgrade and ensuring that no silt, mud, or water remains. Subgrade repairs are then made with a well-graded soil aggregate.

Surface repairs should consist of a well-tamped or rolled-in-place, coarse-graded aggregate of the same gradation as the original surrounding surface.

Blade shoulders so water drains from the surface and all ruts and washouts are filled. Grade shoulder material flush against or slightly below pavement edges to restrict water seepage to the subgrade and to prevent breaking of the pavement edge caused by traffic driving off the pavement onto the shoulder. Replace material displaced from shoulders with material hauled in, as required.

## Stabilized Soil Surfaces

Occasional blading and rolling are necessary to maintain a proper crown and a smooth surface. In dry seasons, sprinkling is necessary to maintain a proper crown, a smooth surface, and high stability and to minimize dust. The traffic areas hold up well in wet seasons. An asphalt treatment may be justified in prolonged dry seasons, if dust and raveling become serious. Careful attention to shoulders and to the drainage system is essential.

Maintenance of mechanically-stabilized soil surfaces and sand-clay surfaces is essentially the same as that for nonpaved and gravel surfaces.

Procedures described for gravel surfaces arc applicable to surfaces that contain considerable coarse aggregate. Procedures described for nonpaved surfaces are applicable to surfaces that contain little or no coarse aggregate.

Bituminous surfaces, soils, and soil-cement may require additional maintenance as described in the paragraphs that follow.

## Rigid Pavements Potholes

Maintenance of rigid pavements is covered in Chapter 15 of TM 5-337. Frequently inspect concrete pavement to detect early signs of failure, and make prompt repairs to prevent minor defects from spreading.

## Crater Repair

Clean potholes and trim them rectangularly with straight, vertical sides running parallel and perpendicular to the centerline. This provides a shoulder against the movement of the patch. Fill the potholes with a stabilized mix of the same character as the adjacent sound area.

This material should be thoroughly compacted in place, one thin layer at a time.

## Ravels

Edge raveling is caused by water softening the foundation material. Before proceeding with the patching operations, reconstruct the shoulder or lower the subdrainage so this condition will not recur. Then build up the foundation. The patching mixture should conform 10 the surrounding area, as for pothole repair.

Bombs, shells, land mines, and cratering charges can produce extensive craters in traffic areas.

Surface damage does not present any unusual repair problem, but explosions may displace or destabilize large areas of the subgrade. Drainage may also be disrupted, allowing water penetrating the broken surface to accumulate and further soften the subgrade.

Satisfactory repairs require the restoration of subgrade stability to support traffic and prevent undue surface settling after repairs have been completed.

## Coral Surfaces

Use the following procedures for crater repairs:

1. Remove, from around the edge of the
crater, all surfacing that is damaged or not
firmly bonded to the base course.
2. Trim the surface and base course to a
sound, vertical edge.
3. Remove water, mud, and debris from
the crater.
The maintenance of well-built coral traffic areas is relatively simple.

Use fresh, raw coral of the proper moisture content for the repair material.

Maintenance is best done during or after a rain while the coral is wet.

Fill low spots, ruts, and potholes by shoveling or dumping coral directly from a truck onto the low spots. Such patches, if rolled while wet, will bond onto the original material almost without a mark. Salt water is usually available where coral is available, and salt water makes a better bond than fresh water.

4. Fill the crater with successive 6- to
8-inch layers of suitable material to the original level of the subgrade. Compaction
is essential; each layer must be thoroughly
tamped with hand or pneumatic tamping tools. After the material has reached a suitable level, compaction equipment can be pulled through or driven across the crater.

5. Repair the base course and wearing surface.

material from the shoulders of roads or airfields may be borrowed and replaced later.

When the situation permits and where enemy action may be anticipated, stockpiles or material pits should be prepared at convenient sites.

Alternate layers of sandbags and tamped earth allow good subgrade compaction where other equipment or materials are not available.

Gravel, rock, masonry debris, sandy soil, or other suitable, stable materials can be used to fill craters, as shown in Figure 8-6.

Material blown from craters can be used for much of this fill. In an emergency.

For a detailed discussion of specific crater repair techniques used in air-base damage repair, refer to Training Circular (TC) 5-340.

## Road Maintenance

The importance of preventive maintenance gineer units. Under the pressure of combat and the necessity for prompt maintenance of all types cannot be overemphasized.

Neglect and delay permit the traffic and weather to turn minor defects in 10 major problems.

Progressive failure of roads is a serious matter. The more serious a failure is, the more quickly it deteriorates. In forward areas, extensive repairs are often necessary before roads can be used. Expedient work is usually done by combat enconditions, temporary repairs are made hurriedly using the materials most readily available. Such repairs are intended only to meet immediate minimum needs. As the advance units move forward, other engineer units lake over the work of additional repair and maintenance. Epedient repairs previously made arc supplemen ted or replaced by more permanent work. Surfaces are brought to a standard that will withstand the required use and maintenance becomes routine.

## Maintenance Patrols

whenever material must be hauled or surface patching accomplished.

Winter weather; severe storms; heavy, destructive enemy action; and other conditions demand that the patrols be reinforced with additional personnel and equipment or that the assigned areas be reduced and the number of patrols increased. Special conditions often call for special equipment.

## Duties

Adequate maintenance requires a workable maintenance organization. Usually engineer units establish a patrol system to handle the roadnet for which the unit is responsible. It is desirable to use squads as patrols and thus retain unit integrity, with each squad commanded by its squad leader and using its regular table(s) of organization and equipment (TOE). The platoon furnishes reinforcements (personnel or equipment) as needed.

The duties of maintenance patrols are as follows:

 - Clean out drainage facilities.
 - Mow grass and weeds.
 - Repair minor washouts and potholes.
Assign each patrol to a specific area. Organize as many patrols as necessary to adequately cover the total area of responsibility. It is sometimes necessary in forward or heavy-traffic areas to provide enough patrols to put the maintenance function on a 24-hour-a-day basis.

## Personnel And Equipment


- Maintain the road surface; for example,
eliminate ruts, potholes, and washboards.
 Z Maintain road shoulders and ditches.
Two plans are presented for the organization of maintenance patrols. Consider the merits of each plan with respect to the maintenance problems of the situation and the personnel and equipment available for the patrols.

 Z Make frequent, thorough inspections of
road conditions, and report to higher
headquarters any need for repair work more significant than the patrol is
equipped or manned to handle.

## Inspection And Supervision

An officer or senior noncommissioned officer (NCO) is assigned several patrols to supervise, assist, and inspect. Normal unit organization should be retained as much as possible. A platoon leader should be responsible for the patrols composed of personnel from his command.

## Repair Crews

One patrol consists of a normal squad equipped with a dump truck, a grader, and hand tools. This patrol can handle all the maintenance and minor repairs normally en countered on a 5- to 15-mile stretch of road. The number of people in a squad "can be decreased and more miles can be assigned to a patrol expected to cover a stretch of permanent pavement in good condition and not heavily traveled. If a patrol is to cover a poor dirt road accommodating heavy traffic, more personnel will be furnished by the platoon and fewer miles will be assigned. Another plan calls for the assignment of a patrol of one to three people, a grader, and hand tools. This crew can handle the routine maintenance on a 12-mile stretch of average earth, gravel, or water-bound macadam road. However, the crew must be supplemented with a truck and repair crew The engineer sending out maintenance patrols should keep sufficient equipment and personnel available to send out repair crews to handle those situations reported by the patrols. The repair crew composition will be dictated by the needs of the particular job in terms of equipment and personnel. Frequently, the regular maintenance patrol can work with the repair crew, but other maintenance and inspection of the patrol's area must not be neglected.

## Maintenance With Traffic

traffic flow should be carefully planned;
proper procedures should be selected; and all labor, material, and equipment should be on hand to complete the work as rapidly as possible.

## Bypasses And Detours

Give full consideration to the importance of keeping traffic flowing with a minimum of interference or delay. Maintenance of shoulders and ditches can normally be performed without interference from, or hindrance to, traffic. Repairs to other drainage structures may delay traffic or slow other repair work. Permanent repairs are often postponed so that temporary and emergency repairs can be made in order to maintain traffic flow.

## Traffic Control

Bridge or pavement failures or the destruction of part of a roadway by floods or combat action may make part or all of the roadway impassable to traffic. In such cases, a bypass or detour around the damaged or obstructed area is necessary. The construction of a short bypass around an obstruction may be preferable to a longer detour on existing roads. A detour may also be used while a bypass is being constructed. Base the decision upon traffic interference, the work involved, and the time available.

Repairs should be made on one-half the surface at a time when surface repairs will deny traffic the use of sections of the pavement. Block off short sections and post guides to regulate traffic and avoid delay.

Conduct a reconnaissance to determine the best possible route when establishing a detour. The road should be as short as possible and must be in condition, or be put in condition, to handle traffic for the period when it will be used.

Use existing roads when possible.

Construct short sections of connecting roads, if necessary.

Check and repair bridges or reinforce them with timber or planking. Clean and repair culverts. If the need for a detour is anticipated, complete this work beforehand.

Detour roads are usually subjected to heavier loads and more traffic than their design specifications. Because increased maintenance is usually required to keep detours passable, stockpile surfacing material along the route, carefully plan maintenance operations, and keep labor and material constantly available.

When single-lane traffic must be used, control traffic by the baton method. With this method, a flagman is placed at each end of the single-lane traffic section. The flagman at one end of the section has a baton or some other distinctive marker.

Working under a prepared plan, all vehicles traveling in one direction are stopped, while those traveling in the opposite direction are permitted to go through. After a suitable time interval, the flagman on the open end of the section gives the baton to the driver of the last vehicle permitted to go through. Upon arrival at the other end of the section, the driver of the last vehicle gives the baton to the flagman. Vehicles are then permitted to travel in the opposite direction until all waiting vehicles have passed through and the driver of the last vehicle carries the baton to the other end of the section. This process continues as long as necessary.

Place signs at detour entrances, road intersections, and turns to direct traffic. Post warning signs at dangerous points. Place other signs or markings, as required, to ensure minimum traffic delay. Install barricades at each end of the road section under repair. Refer to Chapter 8 of FM 5-36 for the types and posting of road signs.

Sometimes two-way traffic can be maintained through blocked-off sections by diverting one stream of traffic to the shoulder of the road.

Grading and stabilization of the shoulder with gravel or bituminous material may be justified in such instances.

Repairs to be performed during

## Safety Of Maintenance Personnel

above the snow, and mark these locations for maintenance crews.

## Snow Fences

Give special attention to the safety of maintenance personnel working where traffic moves past or around them. Use restrictive speed and warning signs, barricades, and flagmen to control traffic and lessen the danger to maintenance personnel. Instruct crew members to avoid stepping into the traveled way and to be continually alert to passing traffic.

Conspicuously mark maintenance vehicles operating in or on the edge of the roadway with red flags, flashing red lights, or similar devices.

## Winter Maintenance

Conduct reconnaissance before winter to determine where snow fences will be needed to control drifting snow. Because it is fine and compacts into a dense mass, drifted snow obstructs traffic more than an equal depth of freshly fallen snow. Drifts form when wind-borne snow is picked up in open spaces, loses velocity, and is deposited in sheltered places. Danger spots, therefore, are roads at ground level or in cuts adjacent to large, open areas. Drifts also form in the lee (down-wind side) of buildings, signboards, and similar wind barriers.

Similarly, high snowbanks left close to the road by snowplows furnish both the conditions and the material for extensive drifting.

Snow fences are not normally required near high fills, in wooded or brushy areas, or where vegetation prevents snow from drifting on the road.

Winter weather may present special prob -
lems in TO maintenance.

Regions of heavy snowfall require special equipment and material to keep pavement and traffic areas in usable condition. Low temperatures cause icing of pavements and frost on subgrade structures.

Alternate freezing and thawing may damage surfaces and tend to block drainage systems with ice. Spring thaws may result in both surface and subgrade failure.

Winter maintenance consists chiefly of removing snow and ice, sanding icy surfaces, erecting and maintaining snow fences, and keeping drainage systems free from obstruction.

## Preparation For Winter

Placement. Place snow fences on the windward side of roads according to prevailing winds (Figure 8-7). The height of the fence determines the distance it is to be placed from the traveled way. Generally, the proper distance is 20 times the height of the fence. This distance is increased where winds are of high velocity. According to the above ratio, a 4-foot fence erected
1 foot above the ground should be placed at least 80 feet beyond the point where drifting is to be prevented. In extreme cases, a distance as great as 300 feet may be necessary.

Organize snow-removal crews and place equipment in readiness. Stockpile abrasives and chemicals in locations where they will be required.

Perform late fall maintenance before the winter freeze. Continue with routine maintenance of ditches and shoulders as far into the winter as possible, so that the drainage system will be in the best possible condition for the spring runoff. Keep earth and gravel surfaces smooth and shaped to prevent moisture from entering the subgrade.

Smoothing and shaping also prevent snowplow blades from being obstructed by rough, frozen shoulder and surface material. In areas of heavy snowfall, outline bridges, culverts, and narrow places in the road with poles that extend Fences should be as long as possible without any holes or openings. Openings provide for dispersion of snow on the back side of the fencing.

The effect of a snow fence in controlling drifts caused by a road cut is shown in Figure 8-8. Two or more parallel fences may be required, but one tall fence is generally better than two short ones. If fences are set too far away, they have little or no effect in reducing drifts. If fences are placed too close to the road, drifts to the leeward side of the fence fall on the road.

windward side.

In regions of heavy snow, use long posts so that fencing may be raised on the posts as the season progresses. This will increase snow storage to the leeward side.

Install fencing with the bottom about 6 inches above ground level to prevent the ends of the pickets from freezing fast and to prevent the fence from choking with snow.

Frozen ends make it difficult to raise the fence and may cause the pickets to break when swayed by the wind.

Brace the posts according to the anticipated wind velocities.

Maintenance.

Inspect snow fences after heavy storms. Repair broken ties and braces, and straighten blown-down sections.

Raise fences to exceed the height of accumulated snow on the leeward side. Lowering of fences may be required after midseason thaws or long periods of settling.

Types of Snow Fences. Commercial snow fences are commonly used. They consist of metal posts and wooden laths or metal pickets about 5 feet long, woven together with wire. Such fencing is portable, easily erected and dismantled, and may be rolled up and stored in the summer. Permanent snow fences include open-board fences on posts and evergreen or deciduous shrub hedges. Plastic snow fencing is lighter and more efficient than wooden fencing.

Removal and Storage. Remove snow fences in the spring and repair damaged sections.

The fences are frequently stored on dunnage at the drift location for use the following winter.

## Snow Removal

Other types of snow fencing include wood slats or pressed-steel slats mounted on collapsible A-frames, worm fences, and brush or branches suspended on wire. Local materials, such as corn stalks, brush, and coarse grass anchored in place by wire or wood, may be used. Figure 8-9, page 8-14, shows three types of snow fences.

Prompt snow removal is essential to prevent traffic interference and ice formation on the road. Begin removal operations when the snow starts.

The amount of equipment necessary depends on the intensity of the storm.

If possible, store equipment at intervals along road sections or roadnets that are to receive early attention, and have operators ready to move promptly when a snowstorm arrives.

Erection. Erect snow fences before the ground is frozen.

Drive metal posts into the ground and mount wire fencing on the disposal point.

When snow removal is delayed or interrupted, the snow may become too deep for available equipment to handle, drifting may worsen, or wet snow may freeze.

Trucks with 2 1/2- to 5-ton capacities and equipped with one-way blades are best adapted for long stretches of roads. This equipment travels at speeds of 15 to 25
miles per hour (mph), removes snow from the road before it is compacted, and provides an open track for traffic.

Provide for relief crews, since snow-removal equipment must frequently be operated on a 24-hour basis during periods of heavy storms.

Use snowplows to patrol areas or sections of roads that are subject to drifting in windy weather.

Standard snow-removal equipment consists of various attachments mounted on trucks or similar prime movers.

These include one-way, reversible, and rotary-type straight blades; straight underbody blades; V-type plows; and rotary snowplows.

These items are described in Chapter 11 of TM 5-624. Graders, dozers, and loaders are also useful in snow removal.

Improvised equipment, such as drags, may be used in expedient situations.

Use 5- to 10-ton trucks equipped with either straight or V-shaped blades for heavier snowfalls and to widen traffic lanes.

This equipment operates at about 15 mph.

Use V-shaped plows to break through heavy drifts.

Use either straight or V-shaped plows equipped with side wings to push the snow beyond the shoulder line, to prevent drifting, and to provide room for additional snow storage.

Use comparatively light and fast snowremoval equipment for light snowfalIs and at the beginning of severe storms. Use heavier equipment to widen traffic lanes and for heavy snowfalls. Continue snowremoval operations until the snow has been pushed back, leveled, or hauled to a inlets or catch basins so they do not obstruct flow.

Trucks used for plowing generally carry abrasives as a ballast for better traction.

Tractors are sometimes required for heavy snows and drifts. Graders are satisfactory for light snow.

In areas of very heavy snowfall, rotary plows and blowers may be needed.

## Surface Ice Control

The formation of road ice resulting from packed snow, slush, or melting snowbanks is prevented if snow removal is effectively performed and drainage is provided. When possible, push snowbanks away from pavements so that melted water will not run onto cleared surfaces.

Use of Abrasives. Treat icy pavements with abrasives and salts to reduce slipping and skidding.

Sand, both treated and untreated; cinders; and crushed rock or slag screenings are commonly used. Other materials include pea gravel, coal stock, and coke screenings. The choice of materials is based on the availability and the length of the haul.

Sharp, angular material embeds itself readily, and dark-colored material absorbs the most heat from the sun. Untreated materials are fairly effective on compacted snow but are easily blown or thrown from the traveled way.

Use plows and graders to remove slush from the road to prevent freezing and icing or to remove ice that has previously formed.

Use care to avoid damaging the pavement.

Dry snow compacts under traffic but can usually be loosened and bladed off without difficulty. Wet snow or slush, if it is allowed to freeze in place, sticks tightly to the pavement and cannot be easily removed without a period of warm weather or the use of salts.

For the most effective use, mix calcium chloride with abrasive material. The calcium chloride causes the abrasive to embed in the ice and improves surface traction.

Treat abrasives with 40 to 75 pounds of calcium chloride per cubic yard for stockpiling, and add another 25 to 50 pounds per cubic yard of calcium chloride when applying it to a road. Sodium chloride may be used in place of calcium chloride but is not recommended for temperatures below 10 F. Store abrasive materials where they are quickly available when needed. Establish stockpiles for hand application at critical locations such as steep grades and curves.

Make wider distribution with trucks by either hand or mechanical spreading. Heating an abrasive material before placing it on the road will allow it to melt into the ice and prevent it from being forced out by traffic.

Various conditions cause icing of road surfaces. Dangerous icing is more likely to occur during the late fall and early spring when frequent temperature changes occur.

Midday thawing and night freezing is a common cause of icing.

Rain; sleet; or light, wet snow falling on cold pavement can form ice films too thin to be removed by mechanical means and can make long sections of the road hazardous. Curves and grades are critical points under icing conditions, and high-crowned roads can become difficult to travel at any point when iced over.

Mechanical Removal of Ice. Graders can sometimes remove ice that is not tightly bonded to the road surface. Extremely icy conditions can be reduced by using scarifiers or rotary tillers equipped with special teeth. Exercise extreme care not to damage the road surface.

Correction of Spring Breakup Problems In regions subject to frost and snow, spring is a critical time in the maintenance of Use of Salts. At the beginning of a storm, apply sodium chloride or calcium chloride to wet snow and sleet to keep it in a slushy condition and prevent it from sticking to the surface.

Limit the use of salts on concrete pavements to one or two applications per year or the pavement will pit and scale.

Salts do not damage bituminous surfaces.

To prevent blockage of the drains by freezing. place bags of salts at drain pavement and other traffic areas. Abnormal and repetitive traffic loads during the spring breakup period may cause subgrade pumping of concrete surfaces and breakthrough of bituminous surfaces. Melting ice and snow, spring rains, and frost leaving the ground all have a tendency to saturate permeable surfaces. Drainage obstructions may raise the water table and make subbases unstable.

Ditches.

When the spring thaw begins, open ditches at critical points so that melted water will not flow onto the road. Outlets of cuts and road sections next to snowbanks require special attention. As the snow begins to melt, snowplows or grading equipment may be required to clear snow from the shoulders to avoid erosion.

Handwork is usually required to clear the shoulders and open ditch outlets. Remove accumulations of ice in culverts and small drainage structures by hand or thaw them with truck-mounted steamers.

## Preventive Maintenance

Frost Heaves. Frost heaves are indicated by the localized raising of road surfaces and pavements. Damage occurs as a result of the heaving of the subgrade soil due to the formation of ice lenses.

This expanding subgrade causes an upheaval of the surface and subsequent reduction in overall strength. Frost heaves are most prevalent in silt and clay subgrades.

The best maintenance of any road is preventive maintenance.

During the spring breakup, the best maintenance of a road subject to frost heaves and boils is to prohibit all traffic during the critical 2- or 3-day period.

Methods to eliminate or minimize the damaging effects of frost action are discussed further in Chapter 12 of FM
5-430-00-2/AFPAM 32-8013, Vol 2.

The approaches and bottoms of fords must be kept smooth and clear of large boulders and debris.

Replace marking posts that have been knocked down or washed out.

Refer to FM 5-446 for additional information.

Frost Boils. Frost boils are indicated by the breaking up of a localized section of road surfaces and pavements when subjected to traffic. During thawing, the melted water produces a fluid subgrade condition with very limited or no supporting capacity. The traffic imposes a force on the pavement and thus to the excess water in the subgrade.

This in turn exerts an equalizing pressure in all directions. This pressure is relieved through the point of least resistance (up through the pavement surface) and produces a small mound similar in appearance to an oversized boil. Frost boils are often large and deep enough to make the road impassable until repaired. Repairs may be made by one or a combination of the following procedures:
Frequently inspect bridge abutments, trestles, piers, and trusses for damage and deterioration.

Repair defects at the earliest opportunity.

The maintenance crew normally obtains help to rebuild or repair the bridge.

 - Bridge soft spots with timber, landing
mats, sapling mats, corduroy, or other
available material. Store materials in
advance at or near load sections where
frost boils may occur. Such repairs are
temporary; therefore, remove the material when the road thaws and dries.
 Z Patch soft spots with crushed rock or
gravel. Place large rocks in soft spots
and cover them with smaller ones. It is better to remove soft, water-soaked
material beforehand, although more
time is required.
 - For best results, provide adequate
drainage along with the repair work to correct the cause of the problem.
Remove soft material and dig an outlet
ditch to one shoulder. A temporary
bridge of planks or other material permits traffic to pass. The excavated soft spot and the ditch are backfilled with rock, gravel, or other suitable material.
Drainage tile may be installed in the
ditch before backfilling.

## Fords And Bridges Airfield And Hellport Maintenance


Repairing and restoring damaged air bases with beyond-emergency repairs.

Developing engineer designs, plans, and
materials to meet Air Force needs as
agreed upon by the Air Force. Where
practicable, designs will be based on the Army Facilities Component System
(AFCS).

Airfield and heliport maintenance is the responsibility of the primary user.

For Air Force air bases, such maintenance is normally clone by an Air Force civil engineering squadron (CES) or similar unit. Army airfields and heliports arc normally maintained by Army engineer units. When the repair and rehabilitation requirements of Air Force bases exceed the immediate, emer gency-damagce recovery capability of the air base, Army engineer units will be assigned to perform the work.

Supplying construction materials and equipment, except for that provided by
the Air Force.

## Air Base Damage Repair

Upon request, assisting within their
capabilities in the removal of UXO declared safe by EOD personnel and
limited damage assessment operations.
The immediate, emergency-damage recovery of air bases generally is considered to be the minimum work required to permit aircraft to land and take off.



Managing and supervising the repair
and restoration of war damage per -
formed by Army personnel. The Air Force base comma nder sets the priorities for air base repair.

## Air Force Responsibilities For Adr

The Air Force provides military troop engineering support from its resources. The Air Force ensures that units arc equipped, manned, and trained adequately to support its needs. This support includes


Emergency repair of war damage to air bases.

Organizing host-nation support (overseas).
The Air Force is primarily responsible for the emergency repair of the air base. This includes the emergency repair of the air base paved surfaces, which is called rapid runway repair (RRR). This is accomplished through the employment of Air Force base civil engineering troop assets; prime base engineer emergency forces (Prime BEEF), and rapid engineering deployable heavy operational repair squadrons, engineering
(RED HORSE) units. The Army is responsible for semipermanent construction, the byond-emergency repair of the air base and, upon request, emergency repairs which exceed the Air Force's capability.

Joint service regulation AR 4 15-30/
AFR 93-10 specifics these repair responsibilities for each service.


Force beddown of units and weapon systems, excluding Army base development
responsibilities.

## Army Responsibilities For Air Base Damage Repair (Adr)


Operation and maintenance of facilities and installations.

Crash recue and fire suppression.
The Army provides engineer support to the Air Force overseas. It ensures that units are equipped, manned, and trained to support Air Force needs. This support includes


Managing force beddown and the emergency repair of war damage.
 Supplying material and equipment to
perform its engineering mission.
 - Assisting in emergency repair of wardamaged air bases where requiremen ts
exceed the Air Force's organic repair capability.
fuselage is an additional maintenance burden.

- Providing logistical support to the Army
for all classes of supply except II, V, VII,
and IX.
- Conducting damage assessment and
removal of UXO.
Mud on airfield and heliport surfaces is either deposited by vehicular traffic from adjacent muddy areas or caused by subgrade failure because of excess moisture and the pumping of mud to the surface under traffic.

- Providing nuclear, biological, chemical
(NBC) collective shelters and establishing and operating personnel and equipment decontamination sites for
the air base and the Army. There are
shortages of these assets on air bases, and support to army units may be
limited.
Enforce mud discipline by limiting access to taxiways only to required service vehicles.

Also, remove mud from the wheels and undercarriages of vehicles before they enter the taxiway. The most satisfactory solution is to provide surfaced service roads to all hardstands.

## Repairs

Air base support agreements may be established in some theaters between the Air Force and the host nation where ADR support capability exists. These host-nation support agreements may include equipment, materials, and manpower assets.

Localized soft or muddy spots in an otherwise satisfactory surface are repaired by replacing the unsatisfactory subgrade material with a more suitable one. If the muddy areas are widespread, it may be necessary to stop all traffic until the surface dries. In extreme conditions, resurfacing may be necessary.

## Mud Removal

For a detailed description of personnel, equipment, and material requirements and critical path schedules for repair of runways cratered by high-explosive bombs, refer to AFR 93-2. For a further, detailed discussion of general ADR, refer to TC 5-340.

## Turf Surfaces

In some instances, surfaces may be kept in operational condition by removing the surface mud. Remove mud by hand shoveling, blading, or dragging.

Light mud or slush is sometimes removed by hand or with rotary brooms.

Plant grass to provide a turf surface on shoulders and all graded areas. Turf aids in camouflage, reduces dust, and minimizes erosion. Turf surfaces are limited to areas where the climate and soil are favorable. Table 8-1 gives the characteristics of many native grasses to aid in selecting proper grass seed or sod.

## Mud Control

Mud on the runway creates slippery surfaces that impede takeoff and increase the difficulties and dangers of landing. Muddy taxiway and runway surfaces decrease tire life and increase the wear and maintenance of brakes.

Flying mud particles may damage propellers, rotors, and jet engines.

Removing mud from wheels, struts, and When a grader is used on a landing-mat surface, take precautions to prevent the blade from tearing the surfacing. A satisfactory method is to bolt a 4- by 12-inch hardwood moldboard over the cutting edge and extending 2 inches below it. This provides a scraping edge with sufficient spring to remove the mud from irregularities in the landing mat, yet soft enough to protect the mat.

A piece of 1/2-inch rubber belting (or the cap from a worn tire) bolted between the blade and the moldboard and extending an inch below the cutting edge makes an effective squeegee for removing light mud and slush. Grader operations for removing mud and slush from the runway are similar to those employed for snow removal. Start in the center of the runway and proceed progressively to the edge, overlapping several feel on each pass.

## Snow Removal And Ice Control

Rollers can be made to any desirable diameter and length with a shell of 10-gage corrugated steel. The shell is supported on an axle by two structural frames, or spiders, at the third points, and two steelplated bulkheads at each end. One plate has a hole to permit filling the roller with sand to increase its weight.

## Clearing And Removing

Snow clearing and removal are required where climatic conditions will not permit packing or where snowfalls arc in excess of that which can be packed on the runway. Remove light snowfalls with a grader or rotary broom. Very light snowfalls can be blown off the runway by the prop wash of Several aircraft lined up along one edge. Remove heavy snowfalls with truckmounted plows, rotary snowplows, rubbertired tractors, or scoop loaders. Drifts may be opened by a truck or tractor with a V-type blade or by a rotary snowplow.

Snow removal methods, the order of operations, and the assignment of equipment arc established in advance of the winter season.

Factors to be considered in planning the snow-handling program are climatic condtions the average snowfall, the aircraft to be accommodated, the equipment available, and the camouflage requirements. Aircraft may be equipped with either wheels or landing skis. Ski-equipped aircraft operate successfully on packed snow.

Aircraft with landing wheels cannot operate in more than 3 inches of loose snow. This limitation applies to fresh snow on a clear runway, fresh snow on previously packed snow, or melting snow previously packed on a runway. For camoflage it is undesirable to remove all snow from a runwav when the surrounding terrain is blanketed with snow.

## Controlling With Equipment

Equip trucks with tire chains and carry ballast for traction while plowing. Keep all blades about 1/2 inch above the runway surface. especially if the surface is a landing mat. This clearance is accomplished by runners mounted at each end of the blade.

Equipment useful for handling snow includes rubber-tired tractors, scoop loaders, graders rotary brooms, and band brooms.

Supplementary equipment may include single-wing one-way, and reversible snow plows: V type plows; rotary plows; blowers;
rollers; and other snow-removal equipment.

## Packing

The assignment of plows varies with the condition at each air field and the type of equipment available. Arranging the plows into units simplifies coordination of snow removal with the control tower. Ordinarily, on c- way, truck -mounted snowplows operate in echelon to expedite snow removal.

Remove snow near landing lights and other obstructions with a blower, if available, or by hand.

In regions of heavy snowfalls with prolonged cold weather relatively free from sudden thaws. snow may be handled by packing. The runway, shoulders, and as much adjacent area as practical arc packed. Rolling begins as soon as 3 inches of snow have fallen and continues during the snowfall. Snow is packed by rollers drawn behind a tractor with snow treads.

The rapid removal of snow requires a rotary blower, snow loader, or other special equipment. Trucks used for hauling snow arc equipped with nigh sideboards. Tractordrawn sleighs built of lumber may be used as an expedient hauling device or to supplement snow-handling trucks.

## Abating Ice Conditions

Smoothing is done with a drag equipped with metal cutting edges on the front and rear or with a grader. Usually one tractor is used to pull both the drag and the rollers, with the drag ahead of the rollers.

Sprinkle ice coatings on runways, taxiwavs, and hardstands with urea, coarse sand, or arrangements must be recognized and accepted.

cinders, spread by hand or by mechanical spreaders. If practical, heat abrasives before spreading.

Remove accumulated abrasives in the spring by brooming, ice conditions on airfields used by jet aircraft arc a very serious problem because abrasives cannot be used. Do not use sodium chloride and calcium chloride for ice control without approval because these salts may promote corrosion of metal aircraft parts.

## Maintenance During Flying Operations

An appraisal of the damage done to a captured field precedes the decision to rehabilitate it. Occasionally, it is necessary to expend more effort to restore a badly damaged airfield than to construct a new one. The damage to the installation includes war damage by our forces in any battle for the airfield and the deliberate damage that the enemy did before yielding the field to our forces. Complete destruction of an airfield is a major undertaking;
therefore, the enemy will likely resort to onc or more of the following less destructive measures:



Placing delayed-action bombs, mines,
and booby traps.

Coordinate maintenance and repair work during flying operations, and plan the work for minimum interference with air and ground traffic.

Much of the maintenance work may need to be done at night or during inclement weather in order not to interfere with flying operations.

Demolishing drainage systems and pavements.

Placing obstacles and debris in the runway.

Plowing turfed areas.
Do not leave equipment hazardous to aircraft on the runway or other areas.

Clearly mark construction or repair areas on the runway so that they are visible from the air. Mark repairs on taxiways so that they are visible to pilots while taxiing.


Flooding surfaced areas.
 Z
Blowing craters in runways, taxiways,
and handstands.

## Rehabilitation Of Captured Airfields


Demolishing buildings, utilities, and similar installations.
Assume these damages were inflicted when conducting such reconnaissance. Use the criteria that follow to prioritize rehabilitation operations:
The decision to rehabilitate a captured enemy airfield and the decision as to the type and construction standard of the rehabilitated field are Air Force and Army responsibilities. The work is ordinarily accompi shed by a combat-heavy engineer battalion. The engineer mission is to convert the existing facilities, which arc usually damaged, to the standard decided upon by the Air Force and Army, with a minimum outlay of labor, equipment, and materials.

Considerable discretion must be exercised in applying standard specifications to captured airfields.

No large-scale relocation of facilities should be undertaken merely to conform to standard patterns, if the existing patterns will serve the same purpose in a satisfactory manner. Sensible, existing substitutions and deviations from specified


- When restoring a captured airfield, the
first priority is to establish minimum
facilities and utilities to include the establishment of a minimum operating
strip for immediate operation of friendly aircraft. This also includes removing UXO, delayed-action bombs, mines, and
booby traps from the traffic areas; clearing debris from those areas; and repairing craters on the runway and taxiway

surfaces. Promptly repair the drainage system. Concentrate runway work first on a minimum operating strip; second, on an access route; and finally, on other traffic areas. Give early attention to the provision of suitable sanitary and water facilities. Chapter 7 of TC 5-340 gives detailed information regarding these areas.

 - The second priority is improvements to
the minimum operational facilities. Restore remaining runways, taxiways,
hardstands, parking aprons, access and service roads, and fuel and bomb storage areas before rehabilitating
other, less vital facilities.
 Z
The third priority is the repair of buildings such as the control tower, operational buildings, crew shelters, communication centers, and other maintenance facilities.
The fourth priority is the camouflage of installations; the restoration of utilities
(making use of any utility map and any available citizen labor familiar with the installation's utilities); and the repair or establishment of bathing, dining, and recreational facilities. A complete cleanup of the grounds, including the removal of debris and seeding and sodding, is the last phase of a rehabilitation project.

Vertical Alignment Spray Applications and Expedient-Surfaced Roads Road Design

## Road Design

Road selection and design depend on the nature of the subgrade; the
traffic and drainage conditions;
                                the construction time available; the
supply of local and imported materials; and the engineer equipment,
personnel, and expertise available.
                                   The completed design must then
meet the requirements for the given load class and allow safe and
efficient
        traffic
               movement.

The load-carrying capacity of a road surface depends on continuous,
stable support furnished by the subgrade. Subgrade stability requires
adequate drainage and proper load distribution by the surface and base
courses.
         Surface and base courses of sufficient thickness and quality
to spread the wheel loads over the subgrade are necessary so that the
applied stress is less than the unit load capacity of the subgrade. in
areas where seasonal freezing and thawing occur. the load-carrying
capacity of inadequately designed or improperly constructed roads can
be dramatically decreased to the extent that failure may occur.

For safe and speedy traffic movement, the geometric design requirement
for given road classes must be met. In a combat zone, military urgency
dictates rough, hasty work designed to meet pressing needs. An im-
proved network of well-surfaced, high-quality roads may be required in
rear areas and near major airfields, ports, and supply installations.
Road design uses stage construction for the progressive improvement
of the road to meet increased traffic demands.
                                                Road design also uses
many technical terms.
                       Figures 9-1 and 9-2, page 9-2, show terms used
to designate road features and components. In addition to this chapter
TM 5-337 provides additional detailed information on the design of
bituminous and concrete-surfaced roads.

## Geometric Design

The geometric design process begins with
1.

Draw the proposed centerline on the good-quality topographic surveys. In most topographic survey.

cases, a minimum 5-foot contour interval is required to clearly describe the terrain.

2. Plot the centerline on plan-and-profile The design process can be described in the paper.

following steps:
3. Calculate grades, the degree of curva-
5. Adjust the centerline, if possible, to ture of horizontal curves, and curve lengths reduce any calculated grades and limit of vertical curves.

horizontal and vertical curves that exceed
4. Compare the values of step 3 with the the specifications.

military road specifications stated in Table
9-1.

the road, multiplied by a factor of two, is suggested as a reasonable estimate. This conservatively assumes that each vehicle uses the road twice (one round-trip) per day.

6. Plot new tangents (straight sections of road) on the plan and profile in those locations where horizontal and vertical curves exceed the military road specifications.

7. Design horizontal and vertical curves for all tangent intersections.

8. Plot newly designed curves on the plan and profile.

9. Develop a mass diagram for the project.

Balance the cuts and fills and optimize ruling grade and earthwork volumes.

Figure 9-3 shows the relationship between DHV and sight distance restriction. If either anticipated DHV or ADT is known and the sight distance restriction can be estimated from preliminary plans, the necessary road type can be determined from Figure 9-3. If ADT or DHV and the road type desired are known, sight-distance-restriction requirements can be determined from Figure 9-3.

10. Design superelevations (curve banking) and widening for all horizontal curves.

11. Draw typical cross sections.

12. Design the required drainage structures and bridges.

## Selection Of Road Type

A range of possible DHV values is given for each road classification in Table 9-1. The actual DHV for a road is a function of the sight-distance-restriction factor, which also has an allowable range for each type of road. The DHV varies directly with a change in the sight-distance-restriction factor. Figure 9-3 shows this straight-line relationship.

After the sight-distance-restriction factor is determined from the design plans of an assumed road class, the actual DHV is determined to ensure that the capacity is adequate.

Example:
A road is to be designed for a military organization having approximately 250
vehicles.

Structural characteristics should accommodate traffic volumes throughout the road's design life.

Table 9-1, page 9-3, shows four possible road types. They are based on expected traffic volumes and show the values for the design control elements for each road class. The capacities arc shown as a range of values. Only road classes B, C, and D apply to TO construction.

If the maximum (or minimum) design value for the various criteria is always adhered to, the resulting vehicle capacity of the road will be on the lower side of the range. Use discretion by designing the road to the best possible standard in a given road class.

## Design Calculation

ADT = 250 x 2 = 500 and DHV = 0.15 x
500 = 75. The 0.15 factor clusters the traffic into rush hours. Otherwise, the hourly volume = 500 vehicles (per day)/24 hours
(per day) - 21 vehicles per hour. Solution:
The calculated DHV of 75 could be met by a class C road. Therefore, assuming a class C road is used, plan-and-profile designs could be drawn and a sight-restriction factor can be determined from the design.

The values in Table 9-1 for each geometric feature must be attained to ensure that the desired road will have a capacity equal to or greater than either the average daily traffic (ADT) or design hourly volume (DHV)
shown.

The first step in the design of a road is to estimate the daily or hourly number of vehicles in a military organization. Where this cannot be done, the number of vehicles organic to the units that will use From Figure 9-3, a sight-distance-restriction factor of 62 percent is determined
(based on a class C road and a DHV of 75).

Using Figure 9-3, the maximum sight-distance-restriction factor for a class C road is
80 percent. This provides a DHV for a class C road of only 30. Since the sight-distance-restriction factor for the example (62
percent) is less than the maximum of 80, this meets the initial requirement of the DHV being greater than or equal to 75.

Therefore, the class C road assumption is adequate.

If a DHV of 75 could not be handled by the class C road, it would be necessary to construct a class B road.

## Estimating Capacity

The information in Figure 9-3 and Table 9-
1, page 9-3, is adequate for the geometric design of military roads. However, additional information is available in TM 5-822-2.

The information can be used to evaluate the capacity of existing roads by obtaining pertinent characteristics and comparing them to the values in Table 9-1. If the data does not conform to that shown for a given road type, use discretion in estimating the road type and ADT or DHV to which the data best conforms. The volume and capacity values in Table 9-1 are for roads of a given class when they are new or in good condition. As the road surface deteriorates, the road is less able to accommodate the traffic compared to the benefits gained by reducing the total number of curves.

for which it was designed. Plan and carry out a maintenance program to keep the road in good condition.

## Grade And Alignment

Tangents should intersect other roads and railroads at right angles. Military roads normally supplement existing roadnets and have intersections at one or both ends of the military road. Operating efficiency usually is improved when these intersections approach right angles. Frequently used horizontal curves are shown in Figure 9-4. The most common are the simple curve, the reverse curve, the compound curve, and the spiral curve.

 - A simple curve uses the arc of a circle
to provide a smooth transition between two tangents.
This curve is used frequently in the TO because it fills the
needs of the low-speed design roads normally used and is easy to construct. A
reverse or compound curve can be
designed using the same basic equations.
Before building a road or an airfield, the engineer must determine the best vertical and horizontal alignment of the facility concerned.

Design both horizontal and vertical alignment to keep sight distance restrictions to a minimum.

Define the route by a series of straight lines and curves to meet the stated mission and capacity. This provides the shortest, most efficient route that requires the least construction effort. Define the route vertically in a series of grades and curves that fall within acceptable specifications and requirements. Horizontal and vertical alignment are interrelated and must be considered concurrently. However, the principles on each are best studied separately. Horizontal and vertical curves of all types are discussed in FM 5-233.

## Horizontal Alignment And Horizontal Curves

The principles of horizontal alignment are summarized as follows:

 Z A reverse curve uses two simple curves
tangent to a common line at a common point. Their centers are on opposite sides of the common line. The radii of the curves may or may not be equal in length.
Tangents (straight sections of road) should be as long as possible, because the shortest distance between two points is the connecting straight line.

Terrain conditions, however, seldom permit the construction of a route between two points in one tangent line. Therefore, the engineer should make each tangent as long as possible, limit the number of curves, and provide long straight stretches, thereby improving the route capacity.

Make curves as gentle as possible. Long, gentle curves increase the capacity of the roadway by permitting higher speeds. They also provide a safer path of travel for the vehicle.

Making gentle, horizontal curves will increase the curve length, thereby decreasing the tangent length. However, this reduction in tangent length is minor

## 9-6 Road Design


The tangent distance (T) is the distance
from the PI to the PC or from the PI to
the PT.

 - A compound curve has two simple curves tangent to a common line at a common point. The centers of these curves are on the same side of the common
line, and the curves have radii of different lengths.
The radius (R) of curvature is the radius of the circle whose arc forms the curve from the PC to the PT.

 Z
The length of curve (L) is the distance from the PC to the PT along the curve,
measured as an arc or as a series of
100-foot arcs. Railroad engineers
measure L as a series of 100-foot chords.

 - A spiral curve is a simple curve in the
center with parts of a spiral on each end to smooth transition to the tangent. The spiral is used only on high-speed roads (classes A and B). Detailed steps
for the design and layout of spiral transition curves are in FM 5-233. Low design speeds of class-C and -D roads do not require spiral transition sections.

## Elements Of A Horizontal Curve

The angle of intersection (I) is the exterior angle at the PI formed by tangents A and B. The central angle, between the radius points at O, is equal to the exterior angle.

The following are elements of a simple, horizontal curve as shown in Figure 9-5:



The external distance (E) is the distance
from the PI to the midpoint of the curve.

The long chord (C) is the straight-line
distance from the PC to the PT.
 - The PC is the point where the curve
begins or leaves tangent Athe tangent nearest the origin of stationing (station 0 + 00) or start of the project.

 The PT is the point where the curve
ends or joins tangent B.
The middIe ordinate (M) is the distance
from the midpoint of the curve to the midpoint of the long chord.
 - The PI is the intersecting point of two
tangents that must be connected by a horizontal curve.

## Degree Of Curvature

nificant (frequently well below 1 percent) for TO construction. However, because the arc definition is the most widely used procedure in road design, only its definition will be used throughout the rest of the chapter.

## Equations For Simple, Horizontal-Curve Design

The two methods commonly used to solve horizontal curve problems are the 1-degreecurve method and the trigonometric method. Both methods may be used with the same degree of accuracy. The 1-degreecurve method requires the Functions of a
1-Degree Curve table shown in Appendix F
of this manual.

The connecting curve between two tangents may be short and sharp or long and gentle, depending on the properties of the circle chosen. Sharpness is defined by the radius of the circle.

For example, a curve may be called a 150-foot curve. However, a curve is seldom referred to by its radius because the center of the curve is often inaccessible on the long, gentle curves used on modern highways. The more practical and common reference term for defining curve sharpness is the degree of curvature (D). The degree of curvature is established as a whole or half degree. The degree of curvature may be stated in terms of either the arc or the chord.

## Arc Definition

The degree of curvature, D, is that angle which subtends a 100-foot arc along the curve.

(See Figure 9-6.) This definition is used by state highway departments and the Corps of Engineers in road design.

## Chord Definition

Appendix F is based on the trigonometric relationships for a curve of D = 1. Curves of different degrees of curvature can be readily designed because of the proportionality between all curves and the l-degree curve. For example, a curve of D =
15 has one-fifteenth the L, E, T, and M
values as for a 1-degree curve (D = 10). The only information needed to obtain the L, E, T, and M values for a 1-degree curve is the angle of intersection (I), and I is always known at the onset of the design process.

The trigonometric method requires a calculator with trigonometric functions or trigonometric tables found in TM 5-236 or any surveying manual.

The degree of curvature, D, is the angle which subtends a 100-foot chord on the curve.

(See Figure 9-7.) This definition results in a slightly larger angle than the arc method, and it is used by the railroad industry and the Corps of Engineers in railroad design.

The difference between the arc and chord definitions is very slight and nearly insig-

## External Distance Radius Of Curvature

Using the 1-degree-curve method (refer to Figure 9-8), the external distance (E) is found as follows:
As previously described in the arc definition, D is that angle subtended by a 100- foot arc on a circle.

By comparing the 100-
foot arc and the total circumference of the circle, an equation for R is developed in terms of D.

## Middle Ordinate

Using the 1-degree-curve method (refer to Figure 9-8), the middle ordinate (M) is found as follows: Length of Curve (L)

## Tangent Distance

In the right triangle shown in Figure 9-5, page 9-7, the vertices are at PC (or PT), PI, and O. The tangent distance (T) is found using the 1-degree-curve method, as follows:
Measure the length of the curve in 100-foot arcs. Because D subtends a 100-foot arc, the total number of such arcs in a horizontal curve must be the number of times that D can be included in the central angle I.

is found in Appendix F, Table F-1, for a given I.

Use Table F-2 to determine the chord correction.

The central angle subtended by the entire horizontal curve has sides that are radii to the PC and PT. Both of these radii are perpendicular to the tangents that form the horizontal curves using the 1-degree-curve method:
1. Find the degree of curvature, D, by one of three methods:
intersection angle I. The quadrilateral formed by the four points of PI (180-I), PC
(900), O (I), and PT (90) must total 360.

1(180-I) + 90 + I + 90 = 360.] Hence, the central angle is equal to the angle of intersection I.

-  If the curve is unrestricted,

## Designing Horizontal Curves

where R = the radius of the curve

Z
If the curve is restricted by the tangent
distance,
The engineer designing horizontal curves must know two facts about the curve from the preliminary survey: the location and station of the PI and the angle between intersecting tangent lines (I). The curves can be designed after this information is obtained.

where
tangent distance for a 1-degree curve
(found in Appendix F, based on the angle of intersection)
restricted tangent distance for a horizontal curve

Z If the curve
distance,
is restricted by the external
The first step is to determine the desired sharpness of the curve. This is defined by the radius or the degree of curvature.

Topographic conditions govern the final location of the centerline and sharpness of the curve. A maximum or minimum tangent distance may fit the terrain conditions, or there may be a limit on the external distance or the middle ordinate. If a restriction exists, solve for the degree of curvature by transposing the equations previously given.

Where no terrain condition dictates the sharpness of the curve, choose a degree of curvature within allowable specifications.

where
external distance for one-degree curve
(found in Appendix F, based on the angle of intersection)
= restricted external distance for a horizontal curve

2. Round up the degree of curvature to the
next half degree when possible.
3. Determine the length of the tangent.
When choosing a degree of curvature, remember that gentle curves are more desirable. However, these long curves may increase surveying and construction time, materials, and effort required. There is no restriction on the length of the curve with respect to a minimum degree of curvature.

However, the maximum allowable degree of curvature is specified by the road classification. Table 9-1, page 9-3, specifies the maximum degree of curvature for each class of road as stated in the row titled "Maximum horizontal curvature."
After the degree of curvature is selected, determine the stations of the PC and the PT. Next, design the curve except for the calculations needed to locate stationing points of the curve between the PC and PT.

The following steps show the design of

5. Calculate the length of the curve.
6. Find the stationing of PT.
P T = P C + L

## Horizontal-Curve Design Examples

This section describes the horizontal-curve design procedures for three common situations:

PC = PI - T = (14 + 28) - (445.29') = (9 + 82.71)
- No terrain restriction which limits T or
E.
PT = PC + L = (9 + 82.71) + (833.33) = (18 + 16.04)
- Terrain restriction of the tangent distance.
Z Terrain restriction of the external distance.
Example:
The station of the PT is determined by adding the curve length to the station of the PC, not by adding T to the station of the PI.

However, the actual point of the PT is found by measuring a distance T (at angle I) from the PI. The station is the distance from the point of origin at station (0+ 00), as measured along the centerline.

Degree of Curvature with No Terrain Restriction. Figure 9-9 illustrates the following computations:
Example:
Given: I = 50, PI at 14 + 28
Terrain Restriction of the Tangent Distance.

Figure 9-10 illustrates the following computations:
Find the station and location of PC and PT for a class C road. Solution:
Given: I = 32, PI at 25 + 87,      is 282' (due to bridge) Find the station and location of PC and PT.

Solution:
A degree of curvature, D, of 6 is selected as a flat, gentle curve. D = 6 is far below the maximum allowable of D = 14.5 for class-C roads and is slightly sharper than the maximum allowable of D = 5.5 for class-B roads.

Knowing that T must not exceed 282 feet and that the D that will give this value is Given: E     85 feet, I = 80, Sta PI at 43 +
32.75
probably not equal to a whole or half degree, it is necessary to first find which D gives 282 feet for off, as shown.

     and then round it If E exceeds 85 feet, the road centerline will be closer than 25 feet to the building.

Find the station and location of PC and PT.

Solution:
If the value of T was specified as exactly
282 feet (as opposed to a maximum or restricted value), the value for D of 550'
must be used. Rounding D up to the next half degree (D = 6) will slightly sharpen the curve and will reduce T slightly below the
282-feet maximum.

Because the limiting value for the external distance and the value used to get this trial value of D are maximums, it is necessary to round to the next higher half degree, thereby decreasing T and E.

Increasing the degree of curvature decreases the values of the radius and tangent distance and vice versa.

When the degree of curvature was changed from 550' to 600', it caused the radius and the tangent distance to decrease from 983.5 feet to 954.9 feet and 282 feet to 273.8 feet, respectively.

Therefore, if the maximum value of the tangent distance is used to determine a trial value of D, the rounding must be to the next higher half degree. If minimum value of the tangent is given, the rounding is to the next lower half degree.

## Example:

Terrain Restriction on the External Distance.

Figure 9-11 illustrates the following computations:

## 9-12 Road Design Station Adjustments Due To Curve Installation

Equations most often will occur at the PT
but may be used anywhere an adjustment to the centerline stationing is required. The equation indicates that an adjustment to the centerline stationing has occurred for some reason.

For example, if the survey crew accidently placed two centerline stakes with the same station number, say 13 + 00, the equation stake would look like this:
Horizontal curves occasionally are designed at the site by the surveying team. When this is done, the route is staked out and stationed progressively along the centerline from the point of origin of the project. It is not necessary to calculate station adjustments required by the shortening of the overall centerline length by a distance of 2T-L. However, when horizontal curves are designed in the office with data supplied by the preliminary survey, the adjustments must be calculated.

The adjustments shown in the preceding equation indicate that the total length of the road has been shortened by the difference of 24 feet in the first example and lengthened by 100 feet (or one station) in the second example.

Equations normally are shown in the profile section of the plans as a gap in the grade with the back and ahead stations written out.

When the preliminary tangent alignment of a route is first determined and stationing along the tangent lines is accomplished, the station of any point represents its distance from the point of origin as measured along straight lines only. When a horizontal curve is installed and becomes the centerline of the route, the stationing distance from the PC to the PT is shortened by 2T-L for each horizontal curve.

## Field Methods Of Curve Layout

The location and station of the PC and PT
of a horizontal curve constitute only two points on the curve.

They do not adequately define the necessary construction. The following methods are applicable to military construction for locating points on the curve:
Arc *Method.* When the radius of a curve is less than 100 feet and topographic conditions permit, locate the center of the circle and swing an arc to locate a curve or fillet, Curves with a small radius are seldom used except at street intersections and for fillets between hardstands, taxiways, or other operational features of an airfield.

In Figure 9-5, page 9-7, the initial centerline distance from the PC to the PT is measured along the two tangents and is equal to 2T. When the curve is installed and the new centerline is created, the final centerline distance from the PC to the PT
becomes L. At this point, the centerline stationed ahead would need to be restationed or adjusted in some manner. To prevent restaking the rest of the project centerline, an adjustment is made to the construction stake at the PT. The method of adjustment will produce a stationing equation at the point of adjustment that will satisfy both the stationing back and the stationing ahead. The equation will have a station which corresponds with the correct station to the rear (or back) and the correct station forward (or ahead). The equation will be written on the construction stake as follows:
where
External-Distance Method. For short curves where three points are adequate for the construction standard desired, calculate the external distance and use it to locate the center of the curve. This method is not recommended for precise construction or for long curves.

It is impractical when the terrain on the curve side of the PI is difficult to negotiate and measure.

Deflection-Angle Method. This method of curve layout usually is the fastest and most

PT = point of tangent EQ = equation BK = correct station back AH = correct station ahead
exact method, particularly for curves with a long radius.

In the arc definition, a deflection angle is the angle formed between a tangent line and a chord from the same point. (See Figure 9-12.)
When laying out a curve, it is common practice to locate stakes at every full station.

In view of this and because the PC of any curve rarely falls on an even station, the first arc will be something less than 100
feet in length (called a subarc). The deflection angle for the subarc to the first full station is the same proportion of D/2
subarc is to 100 feet (Figure 9-14).

that the Once located at a full station, the curve con -
tinues by 100-foot arcs. Therefore, the central angle increases by D and the deflection angle increases by D/2 (Figure 9-15).

NOTE: In other words, the deflection angle is always one-half the intercepted central angle.

If the initial arc is 100 feet long, the central angle will be the degree of curvature D, and the deflection angle will be one-half the degree of curvature D, or D/2, as shown in Figure 9-13.

With the addition of each 100-
foot arc, the total central angle increases by D and the total deflection angle increases by D/2.

The length of the chord for a 100-foot arc on the curve is equal to 2R Sin (D/2).

For the first and last arcs, which are almost always less than 100 feet, the measured chord Is equal to 2R Sin
[(D/2)(L/100)] where L is the distance from the PC or PT to the closest full station.

## Example:

A summary of the deflection-angle and chord-length calculations is shown in Figure 9-16.

In the example of a horizontal curve with no terrain restrictions, the station of PC is
9 + 82.71, the station of PT is 18 + 16.04, and the deflection angles and chord distances are shown in Table 9-2. A useful check on the long series of computations is that the final deflection angle from the PC to the PT must always equal I/2. This is based on the previously stated principle that the deflection angle (from PC to PT) is one-half the total angle subtended (I). This check is illustrated in Table 9-2 for d = 25 = 1/2 =
500/2 for station, (18 + 16.04), which is the PT.

## Layout Techniques

When using the deflection-angle method, set the transit up at the PC. Set zero on the vernier, sight the PI (or take a backsight down the centerline), and turn the first deflection angle. Measure the subarc distance along the instrument's line of sight. To locate the second point on the

## Frequency Of Placing Survey Stakes (In Feet)

Horizontal curves should be staked at a minimum interval of 100 feet. The staking interval on horizontal curves should be based on the degree of curvature and can be determined from the following table:
curve (station 11 + 00), turn the second deflection angle (the angle is measured turning from the PI to station 11 + 00) with the transit still at the PC. Measure the intersection of this line of sight and the 100-foot arc from the preceding station to locate station 11 + 00. Lay out the rest of the curve in this manner.

Degree of Curvature
Radius
Staking
(100')
(meters)
interval
0 to 3
> 1,910'
100'
> 3 to 8
1,910' to 721' 50'
> 8 to 16
720'
to
360'
25'
> 16"
< 360
10'

If the curve is long so that the transit must be moved or if an obstruction prevents a clear line of sight, move the transit to an intermediate station. The same deflection angles previously calculated may be used to locate the rest of the curve.

(See Figure
9-17.)

## Horizontal Curve Design Using Metric Units

The design of horizontal curves using metric units is essentially the same as in English units.

The only difference lies in the relationships of arc length to the degree of curvature as shown in Figures 9-18a,
9-18b, and 9-18c.

If station 17 + 00 cannot be sighted, move the transit to station 16 + 00. Set zero on the vernier, backsight the PC, and turn the angle 2131'6" to sight station 17 + 00. Figure 9-17 shows that angle D must be turned for the transit at station 16 + 00 to become tangent to the curve at that point.

Once the transit is tangent to the curve, angle D/2 must be turned to locate the next station because the arc is 100 feet long. The total angle turned is   + D/2, which is    as originally calculated.

NOTE: The functions of a 1 curve table
are also applicable to metric design based
on the relationship shown in Figure
9-18b. However, if designing using
metric units, the lengths of T, E, M, and
R are in meters.

be based on the degree of curvature and can be determined from the following information:

Degree of Curvature
Radius
Cord Lengths
(100')
(meters)
(meters)

If you design the curve based on       m, but intend on staking at an interval of 20 m, you must determine the degree of curvature based on 20 m        to determine the correct deflection angles. A summary of the deflection-angle and chord-length calculations based on      is shown in Figure 9-18d.

0 to 3
>585
20
>3 to 8
585 to 221
10

Frequency of Placing Survey Stakes (In Meters)

| >8 to 16   |   220 to 110 |
|--------------|--------------|
| >16         |              |
| <110         |            5 |

Horizontal curves should be staked at a maximum interval of 20 meters (m). The staking internal on horizontal curves should NOTE:   is the distance from the PC or PT to the closest full station.

## Vertical Alignment Plotting A Profile View

The capabilities of vehicles or aircraft using any particular road or airfield determine the maximum allowable grades that should be established. However, other factors may be considered. Excessive grades can be installed where speed and capacity are not essential. Whenever possible, grades should be less than the prescribed maximum values stated in Table 9-1, page 9-3.

The profile of a road or airfield is a side view of the project. It represents the horizontal distance, or stations, as abscissa (x axis) against the elevations at these stations, which are plotted as ordinates (y axis).

When a horizontal alignment is set and the project stationed, determine the elevation of critical points along the centerline. Engineers usually calculate the elevation at all half and full stations, PVC, PVT, and HP and LP elevations.

Within limitations imposed by various other criteria, place tangent grade lines so that earthwork is minimized. The earthwork required in most road-construction projects is usually the largest, single work item. Anything that reduces earthwork will improve job efficiency and economy. Attempt to balance the earthwork operations between cut and fill in any area, within the capabilities of available equipment. When drawing the grade lines, the engineer can usually do this balancing by inspection, keeping the profile area of cut equal to the profile area of fill.

These areas are not necessarily proportional to the actual volumes involved, but they serve as a basis for comparison.

It is impractical to baIance a volume of cut with an equivalent volume of fill at a distance beyond the hauling capabilities of the available equipment.

A break point where the prevailing grade makes an appreciable change should be stationed and the elevation ascertained. The most common procedure for determining existing terrain elevations is by a ground survey. However, it is possible to obtain elevations for specific points from a contour map on which the proposed horizontal alignment has been plotted.

Unless the scale of the contour map is large, this method is inaccurate and should be used only for preliminary planning and initial location. The centerline profile may not represent the typical or prevailing condition across the entire section at any particular point. This error may be noticeable when the section is wide, as for an airfield. In such cases, additional profiles may be needed along the shoulder line. It is also possible to make a typical profile that represents the average elevation across the entire section.

Along any proposed route will be points at which the elevation is already fixed. Intersections with existing roads and railroad crossings present predetermined elevations that the engineer must meet when locating the tangent grade lines.

## Plotting Trial Grade Lines

In addition to the controlling specifications for grades, other criteria may control the placement of grade lines. These criteria include the minimum allowable gradients, the maximum allowable change in grade at any Intersection point, the permissible depth of cut or fill, and the maximum gradients in approaching bridges or points of intersection.

After studying the profile, determine the tangent grade lines.

These grade lines serve as the proposed final profile of the project.

It is possible for rough, pioneer construction to follow existing contours with a little smoothing of rough spots. Such a route provides a rough and relatively unsafe roadbed that is not capable of carrying a large volume of traffic. A well-designed route has a series of tangent grades with a smooth transition between them. These tangent grade lines can be determined with a good profile.

## Grade Determination

The degree of steepness measured longitudinally is normally defined as the percentage of grade.

It is established as a relationship between vertical rise or fall for each 100-foot horizontal distance and is expressed as a percentage (per 100).

The equation for determining grades is
where

-  The PVI is the intersection of two grade
lines. This station is always read from
the profile view.
G = percentage of grade V = rise or fall between the two points H = horizontal distance between the two points NOTE: V and H must be in the same units.

-  The PVC is the point along the first
grade line at which the vertical curve begins. The grade line is tangent to the
parabolic curve at this point. By convention. the PVC is always one-half the
length of the vertical curve from the
PVI, measured horizontally.
To differentiate between rising and falling grades along the centerline, a plus sign is used to denote rising grades in the direction of increasing stations and a minus sign is used 10 denote falling grades.

## Vertical Curves

-  The PVT is the point along the second
grade line at which the vertical curve ends. It has the same properties as the
PVC.
Z  The percentage of grade (G) on the
grade line nearest the point of origin is called G1, and the other grade line percentage is called G2. These two grade
lines, which are tangent to the parabolic
curve at the PVC and PVT, intersect at
the PVI.
After grade lines are placed, define the route vertically in a series of grade lines
(straight segments of constant grade) between points of vertical intersection. Design a transition that provides smooth, easy movement from one grade line to another at these intersections. The vertical curves used for this transition and its pertinent dimensions are easily calculated.

## Types Of Vertical Curves

Two types of vertical curves must be considered:
overt and invert.

(See Figure
9-19.) Overt curves are commonly called crest curves, and invert curves are referred to as sag curves. Both types are designed the same way but different specifications govern their dimensions.

## Elements Of Vertical Curves

Figure 9-20 shows a typical vertical curve installed between two grade lines. The parts of a vertical curve include the following:

- The length of vertical curve (L) is the
horizontal distance from the PVC to the PVT. The walking distance along the actual curve has no significance. The PVI
is horizontally midway between the PVC
and PVT. Therefore, the distance from
the PVC to the PVI is L/2, and the distance from the PVI to the PVT is also
L/2.
acteristics of the vehicles or aircraft using the facility.

One criterion (called "r") is expressed as an allowable rate of change of grade for a specific horizontal distance. For example, with a criterion of 0.5 percent change in grade over 500 feet, a      of 1.0
percent requires a curve length of 1,000
feet. However, r is usually expressed as the allowable gradient change in 100 feet of length. The term "r" is frequently used for airfield vertical curve design.

- Offsets    are the vertical distances
from the grade lines to the vertical
curve. The heights of offsets are computed for selected points along the
length of the vertical curve. The selected points are usually at every station and half station.
Sight Distance (S).

When an overt curve is traversed, the ability of the driver to see down the road or airfield is curtailed. If a vertical curve is quite short, the distance that can be seen ahead becomes critically short. Reduced speed is required to reduce the safety hazard. Sight distance depends upon the design speed permitted.

- The maximum offset (MO) is the offset
at the PVI. It is always the greatest offset along the vertical curve.

## Design Of Vertical Curves

Vertical-Curve-Length Factor (k). This factor is used when determining road vertical curve lengths.

It is equal to the horizontal distance, in feet, required to effect a 1-percent change in gradient while providing the minimum stopping distance.

The design of vertical curves includes two tasks-determining the curve length and calculating the heights of a sufficient number of offsets to adequately define or locate the final grade line.

Determination of the Vertical Curve Length.

Determine the vertical curve length by using the vertical-curve-length factor (see Table 9-1, page 9-3) for the given class of road (A, B, C, or D) and for the type of curve.

The factor "k" is used in the following equation:
Length Determination. It is possible to design vertical curves to be long and gentle (flat) or short and abrupt. This is done by varying the curve length. Depending on the facility to be constructed and the standards of construction desired, there are certain limitations on curve length. Minimum lengths usually are specified.

where--

$L=$ length of vertical curve in 100-foot stations

$k=$ vertical-curve-length factor (Table 9-1) $\alpha G=$ change of grade
Change of Grade      The difference in grade between the two grade lines is called the change of grade.

This difference, which Is symbolized as      is computed as which represents the absolute value of The curve installed between two grade lines with a large     which might occur at the top of a steep hill, is longer than the curve required between two grades with a smaller
If length L, as computed, is not in whole stations, round up to the next full 100-foot station.

The length derived by this procedure is compared to the absolute minimum length found in Table 9-1.

Allowable Rate of Change of Grade [r).

Criteria have been established to ensure that the rate at which the change in gradient is made throughout a vertical curve is consistent with the operating char-
Knowing the curve length and the station of the PVI, compute the station of the PVC
and the PVT.

PVC = PVI - L/2 PVT = PVI + L/2

NOTE: The offsets at equal distances
from the PVC or PVT are equal. In other
words, the offsets are symmetric about
the PVI. (This does not mean that the
resulting curve is symmetric (unless    =
    Thus, the offset for only one side
of a vertical curve needs to be calculated.
Therefore, the above equation can be
used to calculate the offset at any point
within the vertical curve.

Offset Determinations. For the curve to be
defined, the engineer must determine eleva-
tions at various locations along the curve.
In order to do so, the engineer must deter-
mine the offset     which is the vertical dis-
tance from the original grade line to the
designed curve.

Elevations Along Vertical Curves. Vertical
curves have the shape of a parabola. Use
the following equation to calculate eleva-
tions along the vertical curve:

Invert curve:

change in elevation + offset

Maximum Offset. As previously stated, the
MO will always be located at the PVI. The
following formula is used to calculate MO:

change in elevation + offset

where

Overt curve:

change in elevation - offset

  MO = vertical height of the maximum
offset in feet
   L = length of vertical curve in sections
     = change of grade in percent

change in elevation - offset

where

Intermediate Offsets. Offsets at locations
along the curve other than the PVI are
referred to as intermediate offsets. Since it
is common practice to stake vertical curves
at whole and half stations, intermediate off-
sets are determined at every whole and half
station along the curve. Use the following
formula to calculate the intermediate offsets:

where

$y$ = elevation of point on curve in feet $d$ = horizontal distance of point on curve from PVC or PVT in stations $\Delta G$ = change of grade in percent $G_{1}$ = percent slope of first grade line $G_{2}$ = percent slope of second grade line $\Delta G$ = elevation at point of vertical curve in feet

High or Low Point of a Vertical Curve.
When the tangent grades             are
equal, the high or low point of the curve oc-
curs at the PVI. (See the following example:)

$\mathbf{\theta}=$ offset at a distance, d, from the PVC or PVT in feet

$\mathbf{d}=$ selected distance (in stations) from the PVC or PVT at which an offset distance is to be calculated

L
   = curve length in stations
   = change of grade in percent

Since     and L have been determined prior
to using this equation, the term       is a
constant.
          Finding the offsets is a simple
matter of varying the value of d.

## Design Steps.

When the tangent grades are the same sign
(both positive or both negative), the high and low points correspond with either the PVC or PVT. (See the following example:)
The following steps show the design procedure for vertical curve:

1. Compute the change of grade.
2. Compute the vertical curve length (L).
When the tangent grades are unequal, the high or low point of the curve always falls on the flatter of the two grades. (See the following example:)
Round up to the next higher full station (if possible).

3.
Determine the PVC. Determine the PVT.
4.
To determine the location along the curve of the maximum (or minimum) elevation, use the following equation:

5.
Determine the elevation of PVC.
where

6.
Determine the elevation of PVT.
d = horizontal distance along curve from PVC (or PVT) in stations

7.
Determine the maximum offset (MO).
L
= length of vertical curve in stations G = percent slope of flattest grade = change of grade in percent

8.
Determine final curve elevations. Compute at every half station and full station
along the curve.
a. Determine grade-line elevations (GLEs). b. Determine intermediate offsets
Cut or Fill Values.

By using the calculated curve elevations and the existing ground elevations, we can determine the cut or fill values to place on the grade stakes for construction operations. The ground elevations can be determined from the profile view established from the initial survey. The difference in elevation between the curve and the ground elevation constitutes the cut or fill value. For example, if the ground elevation at a point on a curve was 86 feet and the curve elevation at that point was 82 feet, the construction stake would indicate a cut of 4 feet (86 feet - 82 feet).

c. Determine curve elevations.
(5) Determine the elevation of PVC.
9. Determine the location of maximum (or minimum) elevation, if required.

10. Determine the highest (lowest) elevation, if required.

(6) Determine the elevation of PVT.
Example:

(7) Determine the maximum offset (MO).
Complete the design of a vertical curve to inelude PVC, PVT, and offsets, with cuts and fills determined every 50 feet (one-half station).

Given:

(8) Determine final curve elevations.
(a) Determine GLEs (Figure 9-21).
The unit survey section has completed a centerline survey for a proposed vertical curve. The road is class D.

Solution:

PVI = 5 + 00, elevation = 73.00'
(b) Determine intermediate offsets
   = +3.1%,    = -5.75%
(1) Determine
NOTE: The term     /2L becomes a constant (1.106).

= 8.85%
(2) Determine L.
From Table 9-1, page 9-3, k for crest vertical curve on a class-D road is 35.

## Use L 4. stations -- 400'
(3) Determine the PVC.
= (3 + 00)
(4) Determine the PVT.
Where
When the known point is at a location other than the PVI, the length of the curve can be determined using the following formula:
= offset from the GLE to the curve d = distance, from the PVC or PVT in stations Where
A = horizontal distance from PVI to known point
  = offset between elevation of known point and GLE of known point NOTE:      must be entered as a decimal.

(9) Determine the location of the maximum or minimum elevation, if required.

Once the length of the curve has been determined, the remainder of the design must be completed according to the vertical curve design procedures previously outlined.

## Example:

(The maximum or minimum elevation is always on the flattest grade when grades have opposite signs.)
Station maximum elevation point =
PVC + d (or PVT - d)
A new road with a PVI at station 12 + 50
and an elevation at 73.00 feet is to pass over a 24-inch culvert at station 11 + 00. The invert of the culvert is at elevation 85.8
feet.

**Station maximum elevation point = ( 3 + 0 0 ) + ( 1 + 4 0 ) = 4 + 4 0**
(10) Determine the highest elevation, if required.

NOTE: + or - is determined by inspection.

## Solution:

y = 66.80 + 4.34 - 2.17 = 68.97
Determine the length of the vertical curve required to clear this culvert with 1 foot of cover.

1. Determine the horizontal distance (A)
from the PVI to the known point.

A = 1,250' - 1,100' = 150'
Vertical Curve Through a Known Point.

When the vertical curve must go through a known point and the known point is at the PVI, the length of the curve can be determined using the following formula:

2. Determine     (as a decimal).
3. Determine the elevation of the vertical curve required to clear the culvert with 1
foot of cover (at the known point).

**ELcurve = 85.8' + 2.0' (pipe diameter) + 1.0' (cover required)**
Vertical-Curve Design Using Metric Units.

The design of vertical curves using metric units is the same as in English units. The only difference lies in the use of meters as units of measurement for elevations and distances.

4. Determine the GLE at the known point
(directly below the culvert).

Frequency of Placing Survey Stakes. Vertical curves should normally be staked at 50-
foot (every half station) or 10-meter intervals. On extremely rugged terrain, the interval should be reduced.

GLE = known point)

## The Crowned Section

GLE GLE = 85.15'
5. Determine the offset    between the elevation of known point and the GLE of known point.

**88.8${}^{\dagger}$ - 85.15${}^{\dagger}$ - 3.65${}^{\dagger}$**
The typical cross section of a road is the crowned cross section. The amount of crown provided depends on the type of surface used. Normal crown slopes are provided in Table 9-1, page 9-3. Figure 9-22
shows a typical cross section for a class-A road. If the road is to be surfaced, the subgrade and the finished surface till have the same crown.

6. Determine the length of the vertical curve.

## Superelevation

The outer edge of a road is elevated to balance the overturning forces experienced by a vehicle rounding a horizontal curve. The amount of superelevation is governed by the degree of curvature (or the curve radius) and the design speed. Detailed information for designing superelevation on

= 388.48' + 246,82' = 635.30'
curves is in FM 5-233. Table 9-3 lists superelevation rates and appropriate transition lengths to develop the superelevated section as a function of the design speed and degree of curvature. Figure 9-23
shows a class-A road section with a superelevated curve.

Table 9-4 lists pavement widening requirements. As shown in Figure 9-24, the transition from a normal cross section on a tangent (A-A) to a fully superelevated, widened cross section on a curve (D-D) is a uniform, gradual change.

The length of highway needed to accomplish this transition is given in Table 9-3. Two-thirds of the specified transition length is affected on the tangent and one-third is affected on the As a safely factor, the pavement width on the inside lane of a curve is increased. The amount of increase is governed by the decurve.

gree of curvature and the design speed.

## Structural Design

In the TO, few roads receive a bituminous or portland-cement concrete surface. Most two-lane roads are surfaced with sand, gravel, crushed rock, or the best locally available material. Expedient surfacing methods are used when required.

This section describes the procedures to improve natural earth surfaces and to resurface them with sand, gravel, or other materials. Included are some common methods of expedient surfacing, guidance, and criteria to determine thickness requirements for bituminous pavements in the TO. The design of mixes and aggregates and the procedures for placing bituminous and concrete surfaces are in TM 5-337. For subgrade and base-course requirements, refer to Chapter
5 of this manual. Additional information in Chapter 12 of FM 5-430-00-2/AFPAM 32-8013, Vol 2, supplements the frost-design procedures in this chapter.

Road surfaces in the TO consist of earth in the most expedient circumstances. When in-place soil is not strong enough, it may be chemically or mechanically stabilized or covered with a bituminous surface treatment. As time becomes available, earthen roads can be improved for increased traffic loads by covering them with material from a borrow pit or with processed material.

## Earth

Many residual oils from oil refineries have been used in this work. In only expedient situations, waste military oils (such as crankcase oils) can be used. The amount of oil ranges from about 1/2 to 1 gallon per square yard and is applied in two or three increments, depending on the type and condition of the oil. The serious environmental, ecological implications of these methods must be considered. Also, using these methods will greatly impair the ability of bituminous admixtures and surface applications to properly cure, if applied later.

Bituminous, stabilized soil mixtures and soil-cement are used as road surfaces to carry light traffic in expedient situations for relatively brief periods. Mechanically stabilized soil mixtures are widely used as surfaces for military roads under favorable conditions. Requirements for mechanically stabilized surfaces are discussed below:
Earthen roads consist of native soils graded and drained to form a surface for carrying traffic. They are designed to satisfy immediate traffic needs and provide a subgrade for surfaces of better quality. Their use is generally limited to dry weather and light traffic. For continued use, periodic maintenance by graders and drags is necessary to maintain a high crown and smooth surface for draining surface water. Dust con - trol must also be provided in dry climates or during dry weather.

Earthen roads become impassable in wet weather because of the rutting action of heavy traffic. Generally, they are used in combat areas where speed of construction is required with limited equipment and personnel.

They are also used as haul roads in construction areas and as service roads for military installations.

## Treated Surface

Gradation requirements for mechanically stabilized soils used directly as surfaces are shown in Table 9-5. Mixtures that have a maximum size of aggregate of 1 to 1 1/2 inches are preferred because the large partitles tend to work to the surface under traffic. Somewhat finer soil is desirable in a mixture that will serve as a surface compared with one used for a base. The finer soil makes the surface resistant to the abrasive effects of traffic and to the penetration of precipitation. Such a surface will Earthen roads may be treated with bituminous materials to control dust and to waterproof the surface. This helps prevent softening of the surface in wet weather.

Treated surfaces are most successful with silt or clay soils.

The bituminous material should be of low viscosity and should contain a wide range of volatile materials of light fractions.

Slow-curing liquid asphalts are frequently used, particularly grades SC-
70 and -250. Medium-curing cutback asphalts, grades MC-30, -70, and
-250, have also been used successfully.

Road tars have been  used to some extent, especially RT-1.

## Stabilized Soil

also more easily replace (by capillary action)
moisture that is lost by evaporation.

Road surfaces require an LL of 35 or less and a PI ranging between 4 and 9. For best results, the PI of a stabilized soil that will function first as a wearing surface and then as a base, with a bituminous surface to be provided later, should be 5 or less.

The LL should be less than 25. Compaction, bearing value, and frost action are important considerations for surfaces of this type.

## Sand Clay

to fine, with a maximum allowable size of 1 inch. Recommended gradation requirements for a gravel surface are given in Table 9-6. A natural pit- or bank-run gravel may meet these requirements without further processing other than screening.

Some pit- or bank-run gravels may require both screening and washing to meet the requirements. River-run gravels normally require the addition of binder to the soil, as do mechanically stabilized soil mixtures.

River-run gravels may also require crushing to provide a rough, angular surface rather than the natural, smooth surface characteristic of river-run materials. The ability to carry heavy, sustained traffic depends on the strength and hardness of the gravel, the cohesiveness of the clay binder, the thickness of the layer, and the stability of the subgrade. These roads can be built rapidly, even in cold weather.

Organizational equipment of combat engineer units is readily adapted to hauling and placing a gravel surface.

One type of mechanically stabilized soil surface is called a sand-clay road. It consists of a natural or artificial mixture of sand and clay that is graded and drained to form a road surface.

Although difficult to obtain, the PI should be less than 5 and LL
less than 25, in case this layer becomes a subbase after placing additional layers above the sand clay. The gradation requirements for a typical sand-clay surface are in Table 5-4, page 5-12, under the column for
1 -inch sand-clay.

The addition of fine gravel (slightly larger than the No. 4 sieve)
usually adds stability.

Like other untreated surfaces, gravel roads require considerable maintenance such as blading and dust control in dry weather.

During wet weather, proper maintenance is difficult, especially under heavy traffic.

Gravel road surfaces with low plasticity make excellent base courses for later-stage pavements.

Sand-clay roads will carry light traffic reasonably well and heavy traffic except under bad weather conditions. The amount of moisture these roads absorb determines their stability under traffic loads. Dust control, blading, and dragging are needed. Sand-clay roads withstand traffic better than ordinary earthen roads, but their use is limited to areas where a suitable mixture of sand and clay occurs naturally or where a deficiency of either is readily corrected.

As a base course for future surfacing, sandclay roads produce poor results, unless the plasticity can be reduced by adding a chemical stabilization agent such as lime.

## Gravel

Gravel roads consist of a compacted layer of gravelly soil that meets the plasticity requirements for mechanically stabilized soil mixtures. The gravel is graded from coarse PROCESSED MATERIALS
requirements in Table 9-6, page 9-29. The information presented here about gravel Processed materials are prepared by crushing and screening rock, gravel, or slag. A
roads generally applies to roads of processed materials.

When gravel or sandcomposite-type surface material should clay is available, processed materials should meet the gradation requirements of Table not be used except when their use will save
9-5, page 9-28.

A coarse-graded type of time and effort.

surface material should meet the gradation

## Expedient-Surfaced Roads

Several types of roads are considered expedient surfaced.

These are unsurfaced roads and roads where some material has been placed on the natural soil to improve the roadway. Types of expedient-surfaced roads include corduroy, chespaling, landing mats, Army track, plank tread, wire mesh, snow and ice, and sand grid.

attach them in place with driftpins. Drive pickets about 4 feet long into the ground at regular intervals along the outside edge of the road to hold the road in place. To give this surface greater smoothness, fill the gaps between logs with brush, rubble, or twigs. Cover the whole surface with a layer of gravel or dirt.

Construct side ditches and culverts as for normal roads.

## Corduroy-Surfaced Roads Corduroy With Stringers

A more substantial corduroy road is made by placing log stringers, as shown in Figure
9-27, parallel to the centerline on about 3-
foot centers.

Lay a standard corduroy over them, Securely pin the corduroy decking to the stringers, and prepare the surface as described in the preceding paragraph.

A corduroy road is an expedient road which uses logs or small trees as the road surface (decking). This method of construction is used in extremely muddy terrain when there is a sufficient supply of natural material. There are three types of corduroy construction: standard corduroy, corduroy with stringers, and heavy corduroy.

## Heavy Corduroy Standard Corduroy

The most frequently used corduroy road, shown in Figures 9-25 and 9-26, is built of
6- to 8-inch diameter logs about 13 feet long. The logs are placed across the road surface adjacent to each other from butt to tip. Along the edges of the roadway, place 6- to 8-inch-diameter logs as curbs and Sleepers (heavy logs 8 to 10 inches in diameter) are used for heavy corduroy roads.

The sleepers must be long enough to span the entire road. Place the sleepers at right angles to the centerline on 4-foot centers.

Build a corduroy with stringers, as shown in Figure 9-28, on top of the sleepers.

capacity of the decking. They serve as a crib, keeping the road surface above the level of the surrounding mud. They sink into the ground until a stratum capable of supporting the load is reached. On fairly firm ground, the standard corduroy may be adequate; on softer ground, stringers are needed, Portable corduroy mats can be prefabricated and put down quickly when needed, They are made by wiring 4-inchdiameter logs together.

weight dis-
Diagonal corduroy is preferred for heavy traffic. It is made by placing the decking at an angle of 45 degrees to the centerline. This modified construction is applicable to all three corduroy types. The angled decking decreases the impact load because each log supports only one wheel at a time and there is longitudinal and lateral tribution.

## Chespaling

Chespaling is a hasty expedient either mud or sand. It is made green saplings, preferably about ches in diameter and 6 1/2 feet

## Choice Of Corduroy Type

Generally, softer ground requires a heavier type of corduroy.

The stringers and sleepers do not increase the bearing used in from small,
1 1/2 inlong. They are wired together to form a 12-foot-long mat as shown in Figure 9-29. Chespaling is often rolled into bundles and carried on each wheeled vehicle. The mats are used to Place the mat so that its long axis is perpendicular to the flow of traffic. If a width greater than the effective length of one plank is required, use half sections to stagger the joints.

A second layer of the steel mat, laid as a treadway over the initial layer, increases its effectiveness.

cross sandy terrain or to get out of mud.

Some mats are constructed from dimensioned timbers wired together to resemble a picket fence. A variation slightly more effective for crossing sand is made by attaching chicken-wire netting to the bottom of the mats. To build a chespaling road, lay a double row of mats, each mat having its long axis parallel to the centerline with a 1-foot overlay at the centerline. Wire the mats together. Keep the road wet to prevent the saplings from becoming brittle and breaking.

Landing mats tend to curl at the edges.

This problem can be overcome by anchoring the edges properly. Screw-type earth anchors furnished with the mat sets provide the best means of anchoring. Another method of securing the edges is to use a curb of timber on the outside edge of the road and either wire it tightly to buried logs laid parallel to the road or stake it. One type of landing-mat surface is shown in Figure 9-30. If MO-MAT (a reinforced plastic material) is available, it may be used as a roadway surface for vehicular traffic.

## Army Track

Bamboo mats are an excellent chespalingtype expedient for beach roadways. These mats are light and comparatively strong.

They are made by splitting 2-inch bamboo rods and weaving them into a mat in a manner similar to rug weaving. Soak the rods before weaving, and keep the mats moist while they are in use. An 11- by 4-foot mat takes about 15 man-hours to construct.

The mats are placed with the long dimension parallel to the centerline. The mats remain serviceable for three or four months on firm ground or sand. Bamboo mats can also be used over mud.

## Landing Mats

A portable timber expedient called Army track, shown in Figure 9-31, can be used to pass vehicles across sandy terrain. The track consists of 4- by 4-inch or larger timbers threaded at each end onto a 1/2-inch wire rope or a 3/4-inch hemp rope. The timbers resemble railroad ties, and a cable runs through them on each side. Space the timbers so that the smallest-wheeled vehicle using the road can obtain traction. Drill cable holes at a 45-degree angle to the centerline so the cable will bend. This practice will prevent individual timbers from moving together.

Anchor the cables securely at both ends. Fill spaces between the timbers with select material to smooth out the surface.

## Plank-Tread Road

The demand for rapidly constructed airfields led to the development of several poriable, metal landing mats. When metal airfield landing mats became a standard supply item in the TO, they were quickly put to use on beaches as well as on airfields.

They are still the foremost expedient for crossing sandy terrain. Landing-mat designs fabricated from aluminum alloys can support heavier loads. They also provide smoother surfaces and have a lower weight per square foot. When used on sand, place the metal landing mats directly on the sand to the length and width desired.

If pierced steel mats are used, place an impervious membrane under the mat to smooth and firm the subgrade, thus improving the road.

The plank-tread road is shown in Figure 9-
32, page 9-34.

To construct a plank-tread road, first place sleepers 12 to 16 feet long, perpendicular to the centerline on 3- to 4-
foot centers, depending on the loads to be carried and subgrade conditions. (If finished timber is not available, logs may be used as sleepers.) Then place 4- by 10-
inch planks parallel to the line of traffic to form two treads about 36 inches apart. Stagger the joints to prevent forming weak spots. If desired, 6-inch curbs may be installed on the inside of the treads.

Use plank roads for crossing short sections of loose sand or wet, soft ground. When built with an adequate base, plank roads last for several months. Planks 3 to 4 inches thick, 8 to 12 inches wide, and at least 13 feet long arc desirable for flooring, stringers, and sleepers. When desired, 3- by 10-inch planks (rough, not finished) can replace the 4- by 10-inch timbers shown in Figure 9-33. Rough 3- by 8-inch and 3- by
10-inch planks can be cut to order.

Position stringers in regular rows parallel to the centerline, on 3-foot centers, with staggered joints. Lay floor planks across the stringers with about 1-inch gaps when seasoned lumber is used. The gaps allow for swell when the lumber absorbs moisture. Spike the planks to every stringer. Place 6-inch-deep guardrails on each side, with a 12-inch gap left between successive lengths of the guardrail for surface-water drainage. Place pickets along each side at
15-foot intervals to hold the roadway in line. Where necessary, use corduroy or other expedient cross sleepers spaced on and reshaping of the surface when ruts appear.

3- to 5-foot centers to hold the stringers in place and to gain depth for the structure. For drainage, construct the base for a plank road with a transverse slope instead of a center crown. To provide a smootherriding surface, place treads parallel to the line of traffic over the floor planks.

## Wire-Mesh Road

Any wire-mesh surface is much more effective if a layer of burlap or similar membrane material is placed underneath it to help confine the sand. (See Figure 9-34.) Lighter forms of wire mesh, such as chicken wire or cyclone fencing, require an extra layer. Often a sandwich type of construction is used-one layer of wire mesh followed by one layer of burlap, then a second layer of wire mesh.

Wire mesh must be kept taut. Anchor the edges of a wire-mesh road at 3- to 4-foot intervals.

Diagonal wires crossing the centerline at a 45-degree angle and attached securely to buried pickets reinforce the light mesh.

Most wire-mesh surfaces are expedient measures. Applied directly to the subgrade, they provide passage for a limited number of vehicles for a short time.

Longer life can be obtained by proper subgrade preparation, multilayer or sandwich construction, and frequent staking. Wire-mesh roads should never be crossed by other roads unless planking or some such material is placed over the mesh to protect it.

## Snow And Ice Roads

Chicken wire, expanded metal lath (used for plastering walls), and chain-link wire mesh may be used as road expedients in sand.

Mesh surfaces should not be used on muddy roads because they prevent grading In regions with heavy snowfall and where temperatures are below freezing for extended periods, expedient roads can be constructed over the snow. When the road is laid out, make grades and curves as gentle as possible. Compact the snow until it is capable of supporting the weight of vehicles. Add water on the compacted snow and allow it to freeze to produce a hard surface. Frozen lakes or streams can be used to move traffic, but first carefully reconnoiter the route for quality of ice, thickness, cracks, and shore conditions.

Determine the load-bearing capacity either by an actual test or by consulting Table 9-7.

## Use Of Polymer Cells (Sand Grid) To Build Sandy Soils

A sand-asphalt surfacing Trafficability over sandy soils is difficult to maintain. The soil strength is adequate, but the soil will displace under a load, due to its cohesionless nature. Wheeled vehicles arc particularly affected. In order to improve trafficability, sand-grid base layers can be used.

is incorporated within the top portion of the sand-grid cells. Its function is to seal the sand into cells and provide a wearing surface for moderate amounts of rubber-tired traffic.

The sand-asphalt surfacing is formed by spraying a suitable liquid-asphalt cement, emulsion, or cutback (rapid-curing (RC) 250
at 165+
Sand grid involves the confinement and compaction of sand or sandy soils in interconnected cellular elements called grids to produce a load-distributing base layer. Uses of the grid include road and airfield pavements, airfield crater repair, erosion control, field fortifications, and expedient dike repair.

Plastic grids (national stock number (NSN) 5680-01-198-7955) are manufactured and shipped in collapsed 4-inch thick, 110- pound sections. (See Figure 9-35.) Each expanded grid section is 8 by 20 feet and contains a honeycomb arrangement of cells.

Each cell has a surface area of 39 square inches and a depth of 8 inches. Grids are delivered in 3,000-pound pallets, each containing 25 collapsed 8- by 20-foot sections.

## 9-36 Road Design Roads In

0 F is preferred) on the surface of

## Site Preparation

Site preparation includes the following steps:

1.
Perform normal cut or fill operations to
reach desircd road grade.
2. Back blade the surface for smoothness.
the sand-grid layer. The asphalt used should penetrate into the top 1/2 to 1 inch of sand in the cells. Over a sand subgrade, such a sand-grid road is capable of handling over 10,000 passes of heavy truck traffic, including tandem-axle loads of up to
53,000 pounds. Avoid tracked vehicles traveling over this road, as their tracks will easily damage the grid cells.

3. Compact the sand subgrade at a moisture content approaching saturation using the vibratory roller.
The following are the procedures for emplacing sand grid.

## Grid Installation Equipment Recommended

Grid installation includes the following Steps:

1. Set up stakes and string lines in 8-foot
by 20-foot boxes.
See Figure 9-36 for
layout patterns.
Equipment recommended for the emplacement of sand grid includes bulldozers;
smooth-bucket (no teeth) scoop loaders;
rough-terrain forklifts; vibratory rollers; water distributors; bituminous distributors; long-handled, round-pointed shovels; and
3/8-inch by 8-foot by 4-foot plywood sheets.

2. Deliver grid pallets with the forklift.
6. Level the joints by placing plywood over the joints and having soldiers walk on top of the plywood.

3. Expand each grid section using three people on each end, pulling outward to slightly over 20 feet, then shaking the section in midair to obtain uniform cell openings. (See Figure 9-37.) Place the section where string lines dictate, (8-foot by 20-
fool steel frames can be ordered.)
4. Shove sand from road shoulders into each end cell and approximately every fifth sirtc-edge cell to anchor the grid in place.

7. Completely fill each grid using scoop loaders.

(See Figure 9-38.) Drop the sand vertically into the cells from a height of at least 2 feet. Do not push the sand forward or the cells will be displaced. Overfill grids by 2 to 4 inches so scoop loaders can operate on the sand-filled grid layer without damaging any cells. Have scoop loaders vary wheel paths to achieve uniform initial compaction of the road.

8. If water is readily available, wet the sand using a water distributor. This will significantly aid in the compaction process.

9. Compact the road surface with one or two passes of the vibratory roller.

5. To construct joints between grids, usc small, 3/8-inch plywood sheets 10 allow soldiers to stand on top of the unfilled grid, allowing access to the joint cells. For end joints, the rounded end cells from different sections should touch each other. For longitudinal (side-by-side) joints, interlock the "welded" cell portions of each section, as if fitting a puzzle. Fill the jointed cells with sand.

10. Remove excess sand from the grid sur-
13. Apply a very light coat (1/4 inch) of face with a grader or by back blading with blotter sand using shovels.

a smooth-bucket scoop loader. Do not use a bucket with teeth, as cell damage can
14. Compact the road using one pass of a result.

11. Recompact the vibratory roller.

9-40.)

nonvibrating roller.
Vibrating the road at
this point will break the asphaltic bonds,
the road with one pass of
(See Figure 9-39, page
15. Apply and compact a 3-inch surface
coat of 1-inch (maximum) gravel, if available. This layer will add a protective cover
12. Spray the asphalt product on the road
material over the sand-grid road, significantsurface and allow enough time for the asly increasing the road life.
phalt product to completely soak into the
grid structure (usually about 10 hours).
(See Figure 9-40, page 9-40.)

## Spray Applications And Surface Treatments

charge) or cationic (carrying a positive charge).

Surface treatments are the most economical troop-constructed surfaces. They require the fewest resources and minimal quality control effort, and they are placed in the shortest period of time. Surface treatments range from single, light applications of bituminous material to multiple surface courses made up of bitumen and aggregates.

Surface treatments can be divided into two categories: sprayed treatments and sprayed bitumen with an aggregate surface.

Spray applications provide soil or aggregate surfaces with the following:
Tars are the residue from the high-temperature conversion of coal to coke. (See Figure
9-43, page 9-44.) They may be modified by cutting them with a light to medium coal oil to form a road-tar cutback. Tars do not dissolve in petroleum products. They become soft and bleed at high temperatures and are brittle at cold temperatures. Because of their susceptibility to temperature change, tars normally arc used only in areas where fuel spills are commonplace, such as tank farms, fuel depots, and aircraft refuel points.

- Prime coat (waterproofing).

## Field Identification

- Tack coat (binding bituminous pavement to surface).
- Dustproofing.
Sprayed bitumen with an aggregate surface provides a waterproof, abrasive, wear -resistant surface with no structural strength. Bitumen with aggregate surface pavements will be either of the following:
Field identification consists of a series of simple tests designed to identify an unknown bitumen product in the field. The purpose of these tests is to determine the uses of a bituminous material and how to use it safely, rather than the exact specifications to which it conforms. Field-identification procedures are applicable to both tars and asphalts.

- Single surface treatment.
- Multiple surface treatment.
Bituminous materials are often found stockpiled in unmarked or incorrectly marked containers. This leads to confusion and delay in construction since the various types and grades of bituminous material are manufactured for a specific purpose.

Field identification is important to the military engineer because

-  Once the type and grade of material are
known, the type of surface that can be
constructed may be determined. The
safety procedures to be followed also
depend on the material identification.
-  Once the surface type is known, the construction procedure may be outlined
and scheduled for a specific target date.
-  Once established, the procedure will
determine the proper equipment for the
job.
Bituminous materials are either tars, roadtar cutbacks, asphalt cement, asphalt cutbacks, or asphalt emulsions. Uses of bituminous materials are shown in Figure
9-41, page 9-42.

Asphalt cement is the heavy material left at the end of the petroleum distillation process. Crude oil is refined into gasoline, kerosene, diesel, motor oil, asphalt, and many other products as shown in Figure 9-42, page 9-
43. Asphalt cement may then be further modified by cutting back the asphalt with some petroleum product, specifically naph -
tha, gasoline, kerosene, or diesel, to form an asphalt cutback. Asphalt may also become an emulsion by mixing asphalt cement, water, and an emulsifying agent together with variable-speed pumps to form an asphalt water suspension. Emulsions are either anionic (carrying a negative does not *pour,* it is an asphalt cement.

Note that at 77 F, even the softest asphalt cement will not pour or deform noticeably if the container is tilted. If it pours, it is a cutback or emulsion. If it is soluble or dilutable in water, it is an emulsion. In addition, the manner in which it pours will furnish a clue to its grade.

Field tests may be performed to identify the bituminous paving material as asphalt cement, asphalt cutback, asphalt emulsion, road tar, or road-tar cutback. In addition, it is necessary to identify as closely as possible the viscosity grade of the bitumen. In order to distinguish among the several asphaltic and tar products, it is necessary to know something of their origin, their physical properties, and the manner in which they are normally used. The identification procedure outlined in Figure 9-44, page
9-46, is based upon the physical properties of these materials.

## Asphalts And Tars

To determine whether a cutback is a RC asphaltic cutback or not, the *smear test* is performed. This is done by making a uniform smear of the substance on a piece of glazed paper or other convenient, nonab -
sorbent surface. This will give the volatile materials, if present, a chance to evaporate.

Since RCs are cut back with a very volatile substance, most of the volatiles will evaporate within 10 minutes. The surface of the smear will then become tacky. This is not true of the lighter grades of mediumand slow-curing asphaltic cutbacks (MCs and SCs), which remain fluid and smooth for some time. An MC will not result in a tacky surface for a matter of hours; for SC materials, several days may be required.

The first procedure in the identification of an unknown bituminous material is to determine whether it is an asphalt or a tar. Asphalts and tars may be differentiated by a simple volubility test. To perform the test, simply attempt to dissolve an unknown sample (a few drops, if liquid, or enough to cover the head of a nail, if solid) in any petroleum distillate. Kerosene, gasoline, diesel oil, or jet fuel is suitable for this test. Since asphalt is derived from petroleum, it will dissolve in the petroleum distillate. Road tar will not dissolve. If the sample is an asphalt, the sample distillate mix will consist of a dark, uniform liquid. If it is a road tar, the sample will be a dark, stringy, undissolved mass in the distil late. A check can be made by spotting a piece of paper or cloth with the mix. The volubility test provides a positive method of identification.

## Grades Of Asphalt Cement

The various grades of asphalt cement are distinguished principally by their hardness, as measured by a field penetration test explained in TM 5-337. This information may be sufficient for planning or, in some cases, actually starting emergency construction.

To identify an 800- or 3,000-grade MC or SC cutback, a *prolonged* smear test is used.

This process is necessary because these grades of MCs and SCs contain such small quantities of cutterstock that they, too, may become tacky in the 10-minute period specified above. A thin smear of the material is made on a nonabsorbent surface and left to cure for at least 2 hours. By the end of that time, if the material being tested is an RC, the smear will have cured and will be hard or just slightly sticky. However, if the material being tested is an MC or SC, the smear will not be cured and will still be quite sticky. If the material is an RC 3,000, it will cure completely in 3 hours, whereas an RC 800 will take about 6 hours. Even after 24 hours, an MC or SC will still be sticky.

## Asphaltic Cutbacks

The pouring or nonpouring quality is one way to distinguish between an asphalt cement and a cutback or emulsion. Asphalt cement is *cutback* with a petroleum distillate to make it more fluid. If the material Since MCs are cutback with kerosene and SCs with oil, this fact may be employed to differentiate between them. Heat is used to drive off the kerosene, if present, and make it show up in the form of an odor. It is best to heat the unknown sample in a closed container in order to capture the escaping vapors, being careful not to apply too much heat. If the sample is an MC, it will have a strong petroleum or kerosene odor. On the other hand, if the sample is an SC, no kerosene or petroleum odor will be detected.

It might smell somewhat like hot motor oil. The ability to distinguish an RC from an MC and an SC from either, is perhaps as important as any other part of field identification.

## Asphalt Emulsions

stringy mass, as shown in Figure 9-44, the material is a tar. The next step is to determine its viscosity grade by the pour test.

By comparing the flow to that of common materials, such as water or honey, the viscosity of the tar may be closely estimated. The grades vary from road tar (RT)-1 to RT-
12. If the identified tar has a viscosity in the range of RT-4 to RT-7 material, a smear test must be performed to determine whether it is a road tar or a road-tar cutback. The smear test is performed in the manner previously described for cutback asphalt. A great increase in stickiness in about 10 minutes identifies a road-tar cutback. No apparent change in consistency after 10 minutes indicates a road tar. It does not matter which grade of cutback is available, since both are used under approximately the same conditions.

## Aggregate Identification

The aggregate must also be tested to determine its suitability for bituminous construction. The desirable characteristics of an aggregate used in bituminous construction include

- Angular and rough.
Z Tough, hard, and durable.
- Clean and dry. - Hydrophobic.
Available aggregate may not always have all desirable characteristics. An aggregate meeting most of the requirements is usually selected, unless rejected for reasons such as availability, length of haul, or difficulty in conducting borrow-pit or quarry operations.

## Angular And Rough

Another asphaltic material used in paving work is an asphalt emulsion, which is a mixture of asphalt, water, and an emulsifying agent. It is easy to identify, since it is usually distinguished by its dark brown color, while the other bitumens are black, If mixed with kerosene or some other petroleum distillate, the emulsion can be detected by the appearance of small black globules or beads which fall to the bottom of the container. If mixed with water, an emulsion will accept the extra water and still remain a uniform liquid. The other bitumens will not mix with water. Since an emulsion contains water, a small piece of cloth saturated with it will not burn if a flame is applied. The other bitumens will burn or flame. After it has been established that the material is an emulsion, it is still important to know whether or not the emulsion is a mixing grade. The best way to tell if the emulsion is a mixing grade
(slow-setting (SS) or medium-setting (MS)) is to try to mix a small amount (6 to 8 percent, by weight) with damp sand using a metal spoon. A rapid-setting (RS) emulsion cannot be mixed; it breaks immediately, gumming up the spoon with the relatively hard original asphalt cement. A SS or MS
emulsion mixes nicely, coating the sand.

Be careful not to add too much emulsion to the sand. This will saturate the sand and not give conclusive results. No further identification is necessary, since both MS and SS grades are largely used for the same jobs.

## Road Tars

The aggregate in a pavement must transmit the traffic load to the base, usually by the interlocking and surface friction of the different particles. Angular particles with a rough texture arc best for this purpose since they do not tend to slide past each other. More binder may be required since If the unknown bituminous material did not dissolve in the volubility test but formed a the angular shape has a greater surfacearea-per-unit volume than a round particle.

sible with the equipment and manpower available.

## Tough, Hard, And Durable Hydrophobic

Affinity for water can make an aggregate undesirable.

If the aggregate is porous and absorbs water easily (hydrophilic), the binder can be forced out of the pores. When this happens, the bond between the aggregate and binder weakens and breaks and stripping occurs. Stripping is the loss of the bituminous coating from the aggregate particles due to the action of water, leaving exposed aggregate surfaces. One of the following three tests can be used to determine the detrimental effect of water on a bituminous mix: Stripping Test. A test sample is prepared by coating a specific amount of aggregate with bituminous material at the applicable temperature for the grade of bitumen to be used. The mixture is spread in a loose, thin layer and air-cured for 24 hours. A
representative sample is placed in a jar (up to no more than one-half of its capacity)
and covered with water. The jar is closed tightly and allowed to stand 24 hours. At the end of 24 hours, the jar with the sample is vigorously shaken for 15 minutes.

A visual examination is made to determine the percentage of exposed aggregate surface which is reported as percent stripping.

The aggregate must withstand loads without cracking or being crushed. Resistance to weathering is also a function of the durability. The resistance-to-wear of an aggregate can be determined by the Los Angeles Abrasion Test, if the equipment is available. The equipment and procedures are detailed in the American Association of State Highway and Transportation Officials (AASHTO) method T96. The equipment for the above test is usually not available for field testing.

The Mob's hardness scale may be used to determine the hardness of the aggregate.

The Mob's scale ranges from
1 for talc or mica to 10 for diamond.

By trying to scratch the aggregate or the common materials and vice versa, it is possible to establish which is harder; from this analysis the hardness of the aggregate can be determined. If both materials scratch each other, the hardness of each is the same. Be sure to rub the "scratch" mark to see that it is really a scratch and not a powdering of the softer material. Some common materials and their hardness are:
fingernail, about 2: copper coin, between 3 and 4; and knife blade, nail, and window glass, about 5.5. If the material can be scratched with one of these common items, it is considered to be soft. If it cannot be scratched, it is considered to be hard.

## Clean And Dry

Swell Test. Asphaltic mixtures containing fines of doubtful quality are sometimes measured for swell as a basis for judging the possible effects on a pavement. This test is more frequently used with densegraded mixtures using liquid asphalts. A
sample of the mix is compacted in a metal cylinder and cooled to room temperature. The specimen and mold are placed in a pan of water and a dial gage is mounted above the sample in contact with the surface. An initial reading is taken. The specimen is allowed to soak for a specified period (usually
24 hours) or until there is no further swelling. Another reading of the dial is taken.

The difference in reading is the swell of the mixture. Experience has shown that bituminous pavement made with clear, sound stone; slag; or gravel aggregate and The bituminous binder must penetrate into the pores of the aggregate and adhere to the surface of the particles. Coated (with clay or dust) or water-filled aggregate will prevent the penetration or the adherence of the binder and result in stripping of the binder. For hot mixes, the aggregate must be hot as well as dry. If the aggregate is not clean, it should be washed either as part of the crushing operation or by spreading it on a hard surface and hosing it with water.

When washing is impractical, dry screening may remove a great deal of dust and clay. Hand picking may be necessary if no other method can be used. The aggregate should be made as clean as posmineral filler produced from limestone will Aggregates of doubtful character should be show test values of less than 1.5 percent.

tested for conformance to ASTM tests.

## Construction Methods Prime Coat

prime material.

If the base is too wet, it will not take the prime properly and the moisture will tend to come out, particularly in hot weather, and strip the prime from the base during construction. Rains also tend to strip the prime from a base that was too wet when primed. Heavy rains may also strip a properly primed base to some extent, but less than an improperly cured base.

In general, the lowest acceptable moisture content for the upper portion of the base course prior to priming should not exceed one-half of the optimum moisture content. On the other hand, if the base dries out completely, cracks may develop and a heavy rain may then cause swelling and loss of density. See Chapter 5 of this manual for subgrade, subbase, and base-course preparation.

## Materials

A prime coat is used when a surface treatment or pavement is placed on a soil or aggregate base. The prime coat should penetrate the base about 1/4 inch, filling the voids. The prime coat acts as a waterproof barrier to prevent moisture that may penetrate the wearing surface from reaching the base.

Also, the bitumen acts as a bonding agent, binding the particles of the base to the wearing surface. Plan priming operations so that there will always be an adequate amount of cured, primed base ahead of the surfacing operations; but not so far ahead that the base will become dirty or completely cured *(dead).* To preserve the base, a prime coat should be applied as soon as the base is ready; however, the prime coat will lose its effectiveness as a bonding agent if the wearing surface is not placed soon after curing.

## Base Preparation

Bituminous materials used for prime coats will depend on the condition of the soil base and the climate. In moderate and warm climates, RT-2, RT-3, RT-4, MC-30, MC-70, SS-1, SS-1h, cationic slow-setting emulsified asphalt (CSS)-1, and CSS-1h are satisfactory. In cold climates, rapid-setting asphalt cutbacks, such as RC-70 and RC-250, have proved more satisfactory. If the climate is very cold, the prime coat may be eliminated because it is likely to be extremely slow in curing. RT-2 and MC-30 are satisfactory for a prime coat used on a densely graded base course.

MC-70 is generally used on loosely bonded, fine-grained soils, such as well-graded sand.

MC-250 is usually satisfactory for coarse-grained sandy soils.

The formula used to determine the quantity of prime coat material required is
The base should be well-graded, shaped to the desired cross section, compacted to the specified density, well-drained, free from excessive moisture but not completely dry, and swept clean.

The surface of the base should be broomed if it contains an appreciable amount of loose material, either fine or coarse, or if it is excessively dusty. When brooming is omitted, apply a prime coat to the base and lightly roll it with a pneumatic roller, or use a light sprinkling of water to settle the dust. Sprinkling is usually undesirable; but when it is necessary, lightly apply a spray of water at the rate of approximately 0.2 gallon to 0.3 gallon per square yard, depending on the condition of the base, the temperature, and the humidity. Completely cover the base with a minimum amount of water and allow it to become dry or almost dry before applying the prime coat so that it will absorb the where
tion of a tack coat. Operation of asphaltsurface-treatment equipment is explained in FM 5-434.

L = length of untreated surface in feet W = width of untreated surface in feet
("+2" in the formula is to include for overspray of shoulders 1 foot on both side of the road. )
AR = application rate of prime coat in gallons per square yard The procedure for estimating the bitumen required for a tack coat is similar to that described for a prime coat except that the tack coat is generally applied only over the proposed width of the pavement. The formula used to determine the quantity of tack coat required is--
NOTE: AR for dense soils = 0.2, AR for soils with a lot of cracks = 0.5
where
LF = handing loss factor for prime coat
(usually 1.05 - 1.10)
  = quantity of prime-coat material in gallons Example:
length of treated section in feet width of treated section in feet rate of application of bitumen in galsquare yard handling loss factor for bitumen (us-
L
=
W =
AR =
ions per LF =
ually 1.05)
   = quantity of tack coat material in gallons Compute the quantity (in gallons) of primecoat material     required to prime an untreated surface with dense soil. The surface is 1,000 feet long and 12 feet wide. Use a loss factor of 1.05.

Solution:

**326.67** **or 327** **eallons**.

The tack coat is generally applied only over the width of the existing area that is to be surfaced.

A tachometer chart may be used to establish the rate of application, The usual rate of application vatries between
0.05 and 0.25 gallon per square yard. On a smooth, dense, existing surface, the minimum rate of 0.05 gallon per square yard should produce a satisfactory bond. If the surface is worn, rough, and cracked, the maximum rate of 0.25 will probably be required. An extremely heavy tack coat may be absorbed into the surface mixture resulting in a bleeding and flushing action and loss of stability. Roll the surface lightly with a rubber-tired roller or truck tires for uniform distribution of the bituminous material. Example: Compute the quantity (in gallons) of tackcoat material    required to cover a worn, rough, and cracked surface. The surface is
1,000 feet long and 12 feet wide. Use a loss factor of 1.05.

A tack coat is a sprayed application of a bituminous material that is applied to an existing wearing surface of concrete, brick, bituminous material, or binder course before a new bituminous pavement is placed over the existing surface. The purpose of the tack coat is to provide a bond between the existing pavement and the new surface. The tack coat should become tacky within a few hours. A tack coat is not required on a primed base unless the prime coat has completely cured and become coated with dust. Figure 9-45 shows the sequence of operations for the applica-
Solution:
with either an asphalt distributor or something as simple as a common watering can.

Rustproofing is usually a short-lived solution and project plans should include regular inspections and maintenance, as required.

## Spraying Asphalt With Covered-Aggregate And Single And Multiple Surface Treatments Dustproofing

Dustproofing consists of spraying an untreated surface with a diluted, slow-setting asphalt emulsion or a low-viscosity cutback The asphalt and dilutent penetrate the fine soil particles and adhere to the dust particles.

A sprayed asphalt with a cover-aggregate surface treatment consists of an application of asphalt followed by an application of aggregate. If the process is repeated, the resulting surfaces arc referred to as double, triple, quadruple, and so on, surface treatments, depending on the number of applications.

Apply these surface treatments on a primed, nonasphaltic base; an asphalt base course; or any type of existing pavement. This type of surface treatment, with a good prime coat (see preceding paragraph), provides the lowest-cost waterproof covering for a road surface. With good aggregate, this type of surface treatment will economically provide a wearing surface to meet the needs of medium and low volumes of traffic.

An asphalt cutback is usually sprayed at a rate of 0.1 to 0.5 gallon per square yard
 . When using an emulsion, dilute it with up to five parts of water by volume. Diluted-emulsion rustproofing treatments usually require several treatments. The dust stirred by traffic between applications eventually conglomerates and no longer rises. This is an effective treatment in very dusty areas where one application of cutback asphalt is insufficient. In all cases, lay a test strip to determine what application rate will be the most effective.

Apply tempt surface treatments when the temperature is below 50 F.

The three requirements for a surface treatment arc as follows:
This type of surface treatment is very useful as a wearing surface on base courses in the staged construction of highways pending placement of asphalt-concrete surface courses.

- The quality of the bitumen must be sufficient to bold the stone without submerging il.
Limitations in the use of sprayed asphalt with cover-aggregate surface treatments are

Z Weather conditions must be favorable.
Z Sufficient aggregate must be used to
cover the bitumen.
- The base course on which the surface
treatment is laid must be sufficiently
strong to support the anticipated traffic
load.
Z The surface on which the asphalt is
sprayed must be hard, clean, and dry for the surface treatment to adhere properly.
Z The amount and viscosity of the asphalt
must be carefully balanced with the size
and amount of cover-aggregate to assure proper retention of the aggregate.
- Heavy, high-speed traffic tends to dislodge the aggregate from the asphalt.
Because of these limitations, consider using plant-mix surface treatments when the above conditions are anticipated.

Uniformly graded sand or crushed stone, gravel, or slag may be used for surface treatments.

The purpose of the surface treatment dictates the size of aggregate to be selected. For example, coarse sand may be used for scaling a smooth, existing surface. For a badly broken surface, the maximum size of the aggregate should be about 3/4 inch; the minimum size should pass the No. 4 sieve. Surface treatments include the following:
dust palliatives, prime coats, and sprayed asphalt with a cover aggregate (single and multiple surface treatments).

## Single Surface Treatment Material

RC and MC cutbacks, road tars, rapid-setting emulsions, and asphalt cements may be used for surface treatment. RC cutbacks are most widely used because they evaporate rapidly and the road can be opened to traffic almost immediately after applying the surface treatment. Viscosity grades of the bitumen depend on the size of aggregate used as cover stone. The larger particles of aggregate require a bitumen of higher viscosity so that the bitumen will hold the aggregate.

For example, RC-70 or RC-250 may be used with coarse sand for a surface treatment to seal cracks in an otherwise satisfactory surface. For resurfacing a badly cracked or rough surface, RC-800 or RC-3,000 may be used with 3/4-inch aggregate. To assure uniform distribution, the bitumen should be applied with a bituminous A single surface treatment usually consists of a sprayed application of a bitumen and an aggregate cover one stone thick. Surface treatment may be referred to as a seal coat, armor coat, or carpet coat. A single surface treatment, shown in Figure 9-46, is usually less than 1 inch thick. Surface treatments serve only as an abrasive and weather-resisting medium that waterproofs the base. They are not as durable as bituminous concrete and may require frequent maintenance. Although they are not recommended for airfields, they may be used as an expedient measure. They are particularly suitable for TO construction because they can be laid quickly with a mini -
mum of materials and equipment, constructed in multiple layers with little inter - ference to traffic, and used as the first step in stage construction. Surface treatment will not withstand the action of metal wheels on vehicles, tracked vehicles, or nonskid chains on vehicle wheels. Do not at-
30 pounds of aggregate are required to cover an area of 1.0 square yard. Solution:

## Requirements For A Surface Treatment

distributor. The quantity of the bitumen required is based on the average particle size of the cover stone. The bitumen must be sufficient to hold the aggregate in place without leaving a sticky surface. The aggregate must not be completely submerged in the bitumen.

One-quarter-inch aggregate should be submerged approximately 30 percent: 3/8-inch aggregate, 32 percent; 1/2-
inch aggregate, 35 percent; and 3/4-inch aggregate, 43 percent.

Approximately 1 gallon of bitumen is usually used for 100 pounds of aggregate.

The recommended rate of bitumen application is given by the following formula:
Example:
In bituminous surface treatments, the unit quantities of bitumen and aggregate can be determined by a test strip, by the specifications of the job, or by adding approximately
1 gallon of bitumen for every 100 pounds of aggregate or 0.1 gallon of bitumen for every
10 pounds of aggregate. The weight of the aggregate, one stone deep, required to cover
1 square yard is determined by spreading the aggregate to be used a depth of one stone over a measured surface, weighing it, and computing the amount in pounds per square yard.

Compute the recommended rate of bitumen application, in gallons per square yard, if

## Multiple Surface Treatment

The formula used to determine the quantity of binder material required for a surface treatment is
where
L = length of treated surface in feet W = width of treated surface in feet
= application of bitumen in gallons per lb of aggregate (usually 1 gal per 100 lb aggregate or 0.01 gal per lb)
    = application of aggregate in lb per square yard When a tougher, more resistant surface is desired than that obtained with a single surface treatment, a multiple surface treatment may be used. A multiple surface treatment is two or more successive layers of a single surface treatment (as shown in Figure 9-
47). Smaller particles of aggregate and correspondingly less bitumen are used for each successive layer. Although multiple surface treatments are usually more than 1 inch thick, they are still considered surface treatments because each layer is usually less than 1 inch and the total surface treatment does not add to the load-carrying capacity of the base.

LF = handling loss factor for bitumen
   = quantity of binder material required in gallons
9 = square feet per square yard
conversion factor Example:
Compute the required quantity of binder material needed for a single surface treatment. The surface is 1,000 feet long and
12 feet wide. Use a bitumen application rate of 0.01 gal per lb of aggregate and a loss factor of 1.05. The aggregate is 3/8-
inch crushed stone with a unit weight of
100
Solution:
Determine the application rate of the aggregate in pounds per square yard.

The first layer of a multiple surface treatment is laid according to instructions previously given for a single surface treatment.

Loose aggregate remain ing on the first layer must be swept from the surface so that the layers may be bonded together. As stated previously, the size of the aggregate and the amount of the bitumen will decrease for each successive layer. For the second layer, the bitumen will usually be reduced to one-third or one-half the amount of the first application.

The aggregate used in the second application should be approximately one-half the diameter of that used in the first application. The final application of aggregate should be swept clean, if necessary, so that an even layer of aggregate will remain. It should also be rolled with a pneumatic roller so that the aggregate will become embedded in the bitumen. After the surface is rolled and cured, it is ready for traffic. If the multiple surface treatment has been laid on an airfield, loose aggregate must be swept from the surface so that it will not damage the aircraft. Final sweeping is also recommended for roads.

Now determine the binder quantity.

## Construction Of Surface Treatments Using Sprayed Asphalt With Covered Aggregate Weather

Weather conditions are an important factor for success in the construction of sprayed asphalt with covered-aggregate surface treatwhat quantity of the aggregate will be required for a specific job. When placing a surface treatment with an aggregate cover, the quantity of aggregate required can be determined from the following formula:
where

L = length of treated surface in feet
W = width of treated surface in feet
LF = handling loss factor for aggregate (10
percent or 1.10).
    = application rate for aggregate
    = quantity of aggregate in tons
ments and seal coats. For best results in aggregate retention, the pavement temperature should be relatively high during the application of the seal coat and considerably lower before fast traffic is allowed to use the new seal coat. A certain amount of curing, or setting, is required even with the heaviest liquid-asphaltic materials.

This curing takes place best when the air temperature is well above 50 F and the relative humidity is low, A survey of surface treatments rated excellent shows more than 85 percent were placed in the hot summer months. Every effort should be made to plan the work for placement in summer weather. After completion of the surface treatment, traffic should be controlled until the surface has cured.

## Aggregate

Once an aggregate has been selected for use based upon the desirable characteristics, it is then necessary to determine The materials for a multiple surface treatment are determined by the same method as above except that the results are multiplied by the number of treatment passes, The aggregate size (not quantity) must be cut in half for the second layer and each layer thereafter.

cient, self-propelled units are most desirable.

Spreading Aggregate. Before the application of asphalt begins, an adequate aggregate spreader should be available and properly adjusted for the aggregate actually to be used. The spray-bar width of the bituminous distributor should be equal to the width of the aggregate being spread in one pass. Normally, this is the width of one traffic lane.

An adequate supply of aggregate should be on hand to cover the asphalt that has been spread, without interruption, in the shortest practical time after the asphalt hits the surface. In addition, the aggregate spreader should be filled, in place, and ready to spread aggregate before commencing the asphalt spray. A common fault is to operate the distributor too far ahead of the aggregate spreader.

Standard, Hopper-Type Aggregate Spreaders.

The standard aggregate spreader shown in Figure 9-48 can handle aggregate which ranges from sand to 1 1/2-inch gravel. The rate and depth of application depend upon the gate opening.

The width of spread may be varied from 4 to 8 feet in 1-foot increments.

Depending upon the manufacturer, the spreader has either two or four wheels.

It hooks on the rear of a 5-ton dump truck and the truck backs up.  This allows the aggregate to be spread on the bitumen ahead of the truck tires, thus preventing pickup of the bitumen. As a safety precaution, men should not be allowed to stand on the aggregate, either in the truck or in the spreader, at any time.

Aggregate spreaders vary from a simple, controllable gate box attached to the dump truck, to very efficient, self-propelled units which apply the larger-size aggregate on the bottom and the finer on top. The more effi-
Rolling.

Pneumatic-tire rollers should be used for surface-treatment construction.

Steel-wheeled rollers are not recommended for rolling, but if they are all that is available, rollers should not be so heavy as to crush the aggregate particles. Pneumatictire rollers are essential to firmly embed the aggregate into low areas or graded deformities that would normally be bridged over by use of steel-wheel rollers and to produce conformity across the width of the roadway, particularly over the outer quarters of the surface where there is the least traffic. The rollers should be heavy enough to properly imbed the aggregate, but rolling should be stopped as soon as crushing becomes evident. When double or triple surface treatments are used, each course should be rolled before subsequent applications of asphalt. When an asphalt fog seal is used, it should be applied after the rolling is completed.

Traffic Control. It is extremely important that traffic be controlled to prevent loss of aggregate. One method of controlling traffic is to form a single line of traffic behind a pilot vehicle with a red flag between stops at each end of the work area.

thermometer should be installed in the tank to readily ascertain the temperature of the contents. A connection should be available to attach a hose for a single- or doublenozzle outlet to cover areas not reached by the spray bars or as a means of forcing a stream of asphalt to a desired point as in subsealing rigid, slab pavements. Distributors are made in sizes ranging from 800- to 4,000-gallon capacity. Some maintenance distributors as small as 400 gallons are available.

## The Asphalt Distributor

It is essential that the distributor be capable of distributing the asphalt uniformly over the surface to be treated. For best results in surface treatments, observe the following points:

- Maintain uniform pressure and temperature on all spray nozzles. The fan of the
spray from each nozzle must be uniform and set at the proper angle with the spray bar (according to the manufacturer's instructions) so that the spray fans do not interfere with each
other.
- Maintain the spray bar at the proper
height above the road surface (according to the manufacturer's instructions)
10 provide complete and uniform overlap
of the spray fans.
Z Ensure that the distributor road speed
is uniform.
The asphalt distributor is the key piece of equipment in the construction of surface treatments.

It consists of a truck (or a trailer) equipped with a mounted, insulated tank with a heating system, usually oilburning, with direct heat from the flue passing through the tank. It is further supplied with a power-driven pump, suitable to handle products ranging from light, cold-application liquid asphalt to heavy asphalt cements heated to spraying viscosity. Attached to the back end of the tank is a system of spray bars and nozzles through which the asphalt is forced under pressure onto the construction surface.

The construction of the spray bars should be such that there will be full circulation of the asphalt through the bar when not spraying.

These spray bars should have a minimum application width of 8 feet. On larger equipment, the spray bars will cover as much as a 24-foot width in one pass when equipped with a suitable capacity pump. The height of the spray bar determines the type of coverage: single lap, as shown in lap, double lap, or triple Figure 9-49. A suitable

Z Before beginning work, check the
spread of the distributor spray bar.
parallel and perpendicular to the centerline of the traffic area.

## Temporary Repairs

Valve action should be instantaneous, both in opening and closing. The spraying operation should be inspected frequently to ensure that the nozzles are the proper height from the road surface and working fully. An otherwise good job may be spoiled if one or more spray nozzles are clogged.

## Of Maintenance And Repair Bituminous Surfaces Inspection

Any stable material may be used for temporary repairs in combat areas or where suitable material is not available and the traffic area must be patched to keep traffic moving. Good-quality soil and masonry or concrete rubble are suitable for this purpose. All such patches must be thoroughly compacted and constantly maintained with replacement material. More permanent patching should be accomplished as soon as possible.

## Maintenance Of Shoulders

Maintenance patrols frequently inspect bituminous pavements for early detection of failures.

Small defects quickly develop into larger ones under the effects of weather and traffic and may result in pavement failure unless promptly corrected. Minor repairs are quickly made with small crews and hand-tools, with a minimum interruption of traffic. Larger bituminous repairs require more time, personnel, and equipment, and may result in interference with traffic or, in extreme cases, require construction of detours to avoid complete stoppage.

Shoulders are bladed to facilitate drainage of rainwater from the surface. Ruts and washouts are filled. Shoulder material is kept graded flush against pavement edges to restrict seepage of water to the subgrade and to prevent breaking of the pavement edge by traffic driving off the pavement onto the shoulder. Material displaced from shoulders is replaced with new material as required.

## Patches

All patches should be trimmed square or oblong with straight, vertical sides running

## General Road Structural Design

NOTE: As mission requirements change
(a forward-area road becomes a rear-area
road), the road class and design index
will change. The design procedures out -
lined in this section allow for the easy
upgrading of roads as the mission chan-
ges. This ensures the ability to easily
convert an unsurfaced road to an ag-
gregate-surfaced road to a flexible-pave-
ment road without major changes in the
design procedure.

## Classes Of Roads

TO roads will normally be designed as unsurfaced, aggregate, or flexible-pavement systems. The design procedure for each type first involves assigning a class (A - G) designation to the road based upon the number of vehicle passes per day. A design category (I - VII) is then assigned to the traffic based upon the composition of the traffic.

A *design index* (1- 10) is determined from the design category and road class. This design index is used to determine either the CBR strength requirements of the unsurfaced roads or the thickness of the aggregate surface or flexible-pavement system required above a soil with a given CBR
strength.

The classes of roads vary from A to G.

Selection of the proper class depends upon the traffic intensity and is determined from Table 9-8.

having three or more axles (Group 3
vehicles) are permitted in this category.

## Design Index

Z Category III. Traffic containing as
much as 15 percent Group 2 but with
not more than 1 percent of the total traffic composed of trucks having three or more axles (Group 3 vehicles).
The design of roads will be based on a design index representing all traffic expected to use the road during its life. The design index is based on typical magnitudes and compositions of traffic reduced to equivalents in terms of repetitions of an
18,000-pound, single-axle, dual-wheel load.

For designs involving pneumatic-tired vehicles, traffic is classified into three groups, as follows:

- Category IV. Traffic containing as
much as 25 percent Group 2 but with not more than 10 percent of the total
traffic composed of trucks having three
or more axles (Group 3 vehicles).
- Group 1. Passenger cars and panel and
pickup trucks.
- Category IVA. Traffic containing more
than 25 percent Group 2 or more than
10 percent trucks having three or more
axles (Group 3 vehicles).
- Group 2. Two-axle trucks (excluding
pickup trucks).
The design index to be used, if designing a road for the usual pneumatic-tired vehicles, will be selected from Table 9-10 based on

- Group 3. Three-, four-, and five-axle
trucks.
Traffic composition will then be grouped into the following categories (summarized for easy reference in Table 9-9):

Z Category I. Traffic composed primarily
of passenger cars and panel and pickup
trucks (Group 1 vehicles) but containing not more than 1 percent two-axle trucks (Group 2 vehicles).
- Category II. Traffic composed primarily
of passenger cars and panel and pickup
trucks (Group 1 vehicles), and containing as much as 10 percent two-axle
trucks (Group 2 vehicles). No trucks
the road class (A to G) and category (I to IVA) .

Where tracked vehicles or forklift trucks are involved in the traffic composition, the following three considerations apply:
Roads sustaining traffic of tracked vehicles weighing less than 40,000 pounds and forklift trucks weighing less than 10,000 pounds will be designed according to the pertinent class and category from Table 9-
10, page 9-59.

Roads sustaining traffic of tracked vehicles heavier than 40,000 pounds and forklifts heavier than 10,000 pounds will be designed according to the traffic intensity and category from Table 9-
12.

- Tracked vehicles not exceeding 15,000
lb and forklift trucks not exceeding
6,000 lb are treated as two-axle trucks (Group 2 vehicles) in determining the
design index.

NOTE:
       DO NOT include any wheeled
vehicles in the total number of tracked
vehicles and forklifts when using Table
9-12.

## Design Life

Z Tracked vehicles exceeding 15,000
pounds but not 40,000 pounds and forklift trucks exceeding 6,000 pounds but not 10,000 pounds are treated as
three-axle trucks (Group 3 vehicles) in
determining the design index.
The life assumed for design is less than or equal to 5 years. For a design life of more than 5 years, the design indexes in Tables
9-10 and 9-12 must be increased by one.

Design indexes below 3 need not be increased.

- Traffic composed of tracked vehicles exceeding 40,000 pounds and forklift
trucks exceeding 10,000 pounds has
been divided into the three categories
shown in Table 9-11.

## Entrances, Exits, And Segments

Regardless of the design class selected for hardstands, special consideration should be given to the design of approach roads, exit roads, and other heavy-traffic areas.

Failure or poor performance in these channelized traffic areas often has greater impact than localized failure on the hardstand itself.

Since these areas will almost certainly be subjected to more frequent and heavier loads than the hardstand, the design index used for the primary road should be used for entrances and exits to the hard stand.

4. Determine the design index from Table 9-10, page 9-59, or Table 9-12. 5. Read the soil-surface strength required to support the design index from Figure
9-50.

In the case of large hardstands having multiple uses and multiple entrances and exits, consideration should be given to partitioning and using different classes of design.

The immediate benefits that would accrue include economy through elimination of excessive design in some areas and better organization of vehicles and equipment.

## Unsurfaced Roads

6, Check whether the design (compacted)
CBR value of in-place soil exceeds the CBR
value required. If the in-place design CBR value is less than the CBR required, the engineer must decide whether 10 decrease the design life or improve the in-place soil to meet the CBR required by one of the following methods:
soil stabilization, soil treatment, or placing aggregate.

An unsurfaced road is one in which the inplace natural soil or borrow soil is used as the road surface. Typically, the construction effort required includes only clearing and grubbing followed by scarifying grading, and compacting.

Designing unsurfaced roads consists of the following steps:
7. Determine the required unsurfaced-soil thickness. Given the required CBR from step 6 and the design index from step 4, the required unsurfaced-soil thickness or depth of compaction can be obtained from Figure 9-51, page 9-62.

## Example (Unsurfaced-Road Design):

1. Estimate the number of passes of each type of vehicle expected to use a road on a daily basis.

2. Select the proper road class based upon the traffic intensity from Table 9-8, page 9-59.

To illustrate the procedure for determining soil-surface strength requirements, assume that an unsurfaced road is to be used one year. The road will be subjected to the fol -
lowing average daily traffic:
3. Determine the traffic category based upon the traffic composition criteria shown in Table 9-9, page 9-59.

quired.

If not, consider using either soil stabilization or an aggregate road.

7. Determine the required unsurfaced-soil thickness from Figure 9-51. Given a design index of 3 and a required CBR of 10.8, the required thickness from Figure 9-51 is 6 inches.

## Solution: Aggregate-Surfaced Roads

1.  Determine the average daily traffic (given). 2.  Select road class E from Table 9-8, page 9-59, based upon 230 vehicles per day.

The design of aggregate-surfaced roads is similar to the design of unsurfaced roads.

However, in aggregate-surfaced roads.

Layers of high-quality material are placed on the natural subgrade to improve its strength.

3.  Select traffic category IVA, based upon the percentage of Group 3 vehicles.

## Materials

4.  The design index is 3 from Table 9-10, page 9-59. 5.  The soil-surface strength reequirement for a design index of 3 is 10.8 CBR. 6.  Check to ensure the design CBR value of the in-place soil exceeds the 10.8 CBR re-
Materials used in aggregate roads must meet the requirements as stated in Chapter 5 of this manual and in the following paragraphs.

The materials should have greater strength than the subgrade and should be placed so that the higher-quality material is placed on top of the lowerquality material.

aggregate; lime rock; and stabilized aggregate may be used without qualification for design of roads, streets, and parking areas.

Specifications for dry and water-bound macadam base courses may be used for design of heavy-duty roads only when the following two conditions arc satisfied:

- The cost of the dry or water-bound
macadam base does not exceed the cost
of a stabilized, aggregate base course.
Z The construction unit has the equipment and expertise to place a macadam surface (wet or dry) to acceptable standards of smoothness and grade.

NOTES:
1. All lifts in a road design must be at least 4
inches.
2. A cohesive soil is one with a PI above 5.
3. A cohesionless soil is one with a PI of 5 or less.
4. Percent compaction Is compared to the
CE 55 curve according to ASTM D1557.

## Select And Subbase Materials

Select and subbase materials used in aggregate and flexible-pavement roads must meet the requirements of Table 9-13.

Design CBR of Base Course. Where subbase material is used for base-course construction, the base course CBR must be at least 50 and the material must conform to the gradation and Atterberg limit requirement for a 50-CBR subbase as shown in Table 9-14. Otherwise, the design CBR of the base course must meet the requirements of Table 9-15, page 9-64.

## Base Course

Only good-quality materials should be used in base courses of heavy-duty aggregate roads.

Specifications for graded, crushed Gradation Requirements. Gradation requ irements for aggregate-surfaced roads and for macadam base courses are given in Chapter
5.

in its natural state. However, in cases where
the moisture content is out of the specifica-
tion range, it may be necessary to scarify
the soil (thereby aerating the soil to adjust
the moisture content) and then compact.
This process is called scarify and compact
in place (SCIP).

Special Subgrades. The procedures for com-
pacting subgrades of clays that lose
strength when remolded, silts that become
quick when remolded, and soils with expan-
sive characteristics are described in Chap-
ter 5 of this manual.

Subgrade in cuts and fills must have den-
sities equal to or greater than the values
shown in Table 9-13, page 9-63, except
that fills will be placed at no less than 95
percent density for cohesionless soils or 90
percent for cohesive soils.

Thickness Requirements. Thickness requirements for aggregate-surfaced roads are determined from Figure 9-52, page 9-65, for a given soil strength and design index. The minimum thickness requirement will be 4
inches.

Where this is not the case for cuts, the subgrade must (1) be compacted from the surface to meet the densities shown; (2) be removed and replaced, in which case the requirements given above for fills apply; or (3)
be covered with sufficient select material, subbase, and base so that the uncompacted subgrade is at a depth where the in-place densities are satisfactory. Depth of Compaction. Compact the subgrade to the depth specified in Table 9-16, page 9-66, for cohesive soils (PI > 5) and Table 9-17, page 9-66, for cohesionless soils (PI   5).

Figure 9-52 provides the thickness of aggregate based on CBR and design index. The thickness determined from the figure may be constructed of compacted granular fill for the total depth over the compacted subgrade or in a layered system of granular fill with subbases for the same total depth.

The layered section must be checked to ensure that an adequate thickness of material is used to protect the underlying layer based on the CBR of the underlying layer.

The granular fill may consist of base, subbase, and select material, provided the top
4 inches meet the gradation requirement ts

## Compaction Requirements

NOTE: When depth of compaction from
Table 9-16 or 9-17 is not feasible or at-
tainable in cut sections, perform a 6-inch
SCIP and continue design based on the
uncompacted subgrade CBR.

Cornpaction requirements for the subgrade
and granular layers are expressed as a per-
cent of maximum CE 55 density as deter-
mined by using MIL-STD-621 Test Method
100.

Select Materials. The procedure is the same
as for the subgrade.

Subbase.
          Compact the subbase to not less
than 100-percent CE 55 density.

Normal Subgrades.
                  Compact the subgrade
to 90-percent CE 55 density for cohesive
soils (PI>5; LL>25) and 95-percent for
cohesionless soils

Base Course.
             Compact the base course to
the maximum degree practicable but not
less than 100-percent CE 55 density.

NOTE: It may be possible to compact the
subgrade material to the required density

Design Steps for Aggregate-Surfaced Roads
6. Determine the depth of compaction for the subgrade soil from Table 9-16 or 9-17,
7. Determine the total road-structure thickness and cover requirements.

1. Estimate the number of passes of each type of vehicle expected to use the road on a daily basis.

2. Select the proper road class based upon the traffic intensity from Table 9-8, page 9-59.

a. Enter Figure 9-52, page 9-65, for each layer of soil or aggregate with the following information:
Design index.

Design CBR values for subgrade, select, and subbase materials.

3. Determine the traffic category based upon the traffic-composition criteria given in Table 9-9, page 9-59.

4. Determine the design index from Table 9-10, page 9-59, or Table 9-12, page 9-60.

b. Determine the minimum cover thickness, in inches, for each layer of the aggregate road structure.

5. Check soils and construction aggregates using standard criteria in Tables 5-4, page 5-12; 9-14, page 9-63; and 9-15, page 9-64.

8. Determine the required percent compaction in terms of CE 55 for each layer from Table 9-13, page 9-63.

9. Draw the section of the aggregate road structure, as shown following.

Available material CBR:
Natural subgrade = 5 (clay, PI = 15)
Design (compacted) subgrade = 8
Clean sand subbase = 30
Lime rock = 80; meets gradation requirement
for maximum size aggregate of 1".

## Solution:

1. Number of daily passes = 70 (given).

2. Select road class F from Table 9-8, page 9-59, based upon average daily traffic of 70.

3. Select traffic category VII from information previously given, based upon the presence of the 60-ton tracked vehicle.

4. Select design index of 9 from Table
9-12, page 9-60. NOTE: You must round the average daily tracked-traffic value of 35 to the next higher value (40) in Table 9-12.

5. Clean sand CBR 30. (Suitable for subbase CBR 30.) Crushed rock CBR 80. (Suitable for base course.)
6. Depth of compaction based on CBR 5 for compacted subgrade is 15 inches. (See Table
9-17. 7. Determine the road-structure thickness required to support a design index of 9.

Example (Aggregate-Road Design):
a. First, look at the required road thickness if the subgrade was not compacted to the design CBR. In this case, the natural subgrade CBR 5 is used in Figure 9-52. This results in a required total thickness of 16 inches, as shown.

An aggregate-surfaced road is to be used for two years. The road will be subjected to

Average
Vehicle
Daily Traffic
M998 HMMWV
10
M929 5-ton
25
dump truck
(dual axle)

b. Now, look at the required thickness when the subgrade is compacted, In this case, the design subgrade CBR = 8 is used in Figure 9-52, resulting in a required total thickness of 12 inches, as shown.

| M729 combat      |
|------------------|
| engineer vehicle |
| (CEV) (60-ton    |
| tracked vehicle) |

8. The required percent compaction of each layer is determined from Table 9-13, page
9-63, as follows:

Crushed rock base course: 100-105 percent
Clean sand subbase course: 100-105 percent
Compacted subgrade-since the PI = 15, it is a
cohesive soil: 90-95 percent

9. Draw the section of the aggregate road
structure. Since two sections were
designed, one with a subbase and one
without, both should be drawn.

Notice how compacting the subgrade greatly reduces the required thickness of the cover material. This is why the subgrade is always compacted.

a. First, design the section without the subbase layer.

c.

Finally, look at the total thickness and required cover for each layer when the subgrade is compacted and a clean sand subbase with CBR 30 is used. First, the design subgrade CBR 8 is used in Figure 9-52, page 9-65, to determine the 12-inch total thickness required above the compacted subgrade. Next, the clean sand CBR 30 is used in Figure 9-52
to determine the required cover of 4 inches above the subbase. This results in the section, as shown.

Notice how the addition of the clean sand subbase reduces the required thickness of the mom expensive lime rock.

vehicles or more per day. Where conditions warrant, use these mixtures to pave roads having traffic volumes of less than 3,000 vehicles per day.

Select exact percentages of bituminous materials on the basis of design tests described in TM 5-337.

be Given that the base-course material is more expensive than the clean sand subbase, section b would be the most economical design.

Note, however, that all possible design sections for the available materials must be evaluated economically. There may be rare instances where the subbase material may be more expensive than the base course. In that case, only the base course would used.

Cold-Laid, Bituminous-Concrete Plant Mix.

Where hot-mix, bituminous-concrete mixtures are not available, use cold-plant, bituminous concrete to pave areas subject to pneumatic-tired traffic only.

## Bituminous Pavements

Bituminous-, or flexible-, pavement designs permit the maximum use of readily available local construction materials. They are easier to construct and upgrade than rigid pavement designs.

Thus, they permit greater flexibility in responding to changes in the tactical situation.

Sheet Asphalt, Stone-Filled Sheet Asphalt, Sand Asphalt, or Sand-Tar Mixes. Fine-aggregate mixes may be used for binder and surface courses of roads with traffic volumes of 2,000 or fewer vehicles per day when sand or other suitable fine aggregates are the only aggregates available. These mixes should not be used as surface or binder courses for roads or industrial-use pavements designed for solid, rubber-tired or steel wheels. In all cases, mixtures made with these aggregates should conform to the criteria for low-pressure tires (100
psi or less), based on laboratory tests.

Flexible-pavement design procedures are different from airfield design procedures. This chapter is limited to flexible-pavement designs for roads.

Chapter 12 of FM 5-430-
00-2/AFPAM 32-8013, Vol 2 covers airfield flexible-pavement designs. TM 5-822-6 covers rigid-pavement designs.

## Pavement Types And Uses

Penetration Macadams. Do not use penetration macadam for paving any areas subject to traffic from tracked vehicles.

The descriptions, uses, advantages, and disadvantages of bituminous pavements and surfacing presented in TM 5-337 are applicable to TO construction except as modified in the following paragraphs. However, when surfacing for steel treads is necessary, use an asphalt cement with a penetration grade of 50-60 or 60-70, depending on the climate or season.

Bituminous Road Mix. Use road mix as a wearing course for TO roads or as the first step in stage construction for more permanent roads.

When the existing subgrade soil is suitable or satisfactory aggregates are nearby, road mixing saves time in handling and transporting aggregates as compared with plant mixing. When properly designed and constructed, the quality of road mix approaches that of cold-laid plant mix. Road mix is used for binder and surface courses. It is generally considered inferior to plantmix pavements manufactured in standard plants because of the less accurate control.

Special consideration must also be given to the design and construction of bituminous pavements that will be subjected to traffic of tanks and solid, rubber-tired vehicles. Most often the number of passes of tanks and solid, rubber-tired vehicles governs the bituminous-pavement design.

## Flexible-Pavement Structure

A typical flexible-pavement structure is shown in Figure 9-53, page 9-70, and illustrates the terms used to refer to the various layers.

Hot-Mix, Bituminous-Concrete Pavements.

Dense-graded, hot-mix. bituminous-concrete mixtures are well-suited for paving heavyduty traffic roads with volumes of 3,000

## Materials

Materials used in flexible pavements must meet the requirements as stated in Chapter
5 and in the following paragraphs:

## Select Materials And Subbase

Select materials and subbases used in bituminous pavements must meet the same requirements as for aggregate-surfaced roads as indicated in Table 9-14, page 9-63.

## Base Course

The base course used in bituminous pavements must meet the same requirements as for aggregate-surfaced roads as indicated previously. except as noted below.

NOTE: Not all layers and coats are present In every
flexible-pavement structure. Intermediate courses may be
placed In one or more lifts. Tack coats maybe required on
the surface of each intermediate course.

Design CBR of Base Course. Where sub-
base material is used for base construction,
the base course CBR must be at least 50
and the material must conform to the Atter-
berg limit requirement for a 50-CBR sub-
base as shown in Table 9-14. Otherwise,
the design CBR of the base course must
meet the requirements of Table 9-18.

Base Course Gradation Requirements. The gradation requirements of the base course are as indicated in Chapter 5 of this manual.

The base course for a flexible pavement must meet the same gradation requirements of Table 5-4, page 5-12, since the flexible pavement will transfer most of the shear stress caused by the load directly to the base course.

A bituminous pavement may consist of one or more courses depending on stage construction features, job conditions, and the economical use of materials. The pavement should consist of a surface course, an intermediate (binder) course, and a leveling course, when needed. These should be thick enough to prevent displacement of the base course because of shear deformation, to provide long life by resisting the effects of wear and traffic abrasion, to be waterproof, and to minimize differential settlements.

## Sources Of Supply

If time and conditions permit, investigate subgrade conditions: borrow areas; and all sources of select materials, subbase, base, and paving aggregates before designing the pavement. In determining subgrade conditions in cut sections of roads, conduct test borings deeper than the frost penetration depth. The minimum boring should never be less than 4 feet below the final grade.

underlying layer based on the CBR of the underlying layer.

## Compaction Requirements

Minimum Base-Course Thickness. The minimum allowable thickness of the base course will be as shown in Table 9-19; except that in no case will the total thickness of pavement plus base for classes A
through D roads be less than 6 inches.

Compaction of the subgrade, subbase, and base course must meet the same requirements as for aggregate-surfaced roads. In addition, an asphalt base course and pavement must be compacted to CE-55 density of 98-100 percent.

The compaction criteria and CBR requirements for a bituminous pavement are summarized in Table 9-20, page 9-73.

Bituminous-Pavement Mix. Bituminous-pavement-mix design consists of selecting the bitumen and aggregate gradation, blending aggregates to conform to the selected gradation, determining the optimum bitumen (asphalt cement) content, and calculating the job mix formula.

Bituminous-mix design is beyond the scope of this manual and is de-
Bituminous-Pavement Design Design Requirements. Flexible-pavement described in detail in Chapter 4 of TM
5-337.

sign must provide the following:
Bitumininous-Pavement Thickness Require-


Sufficient compaction and testing of the
subgrade and each layer during construction to prevent objectionable settlement under traffic.
ment.  Thickness design requirements are given in Figure 9-54, page 9-72, in terms of CBR and the design index determined. Minimum thickness requirements are shown in Table 9-19.

Z
Note that each layered section must be checked to ensure that an adequate thickness of material is used to protect the

Adequate drainage of the base course,
when frost conditions are a factor, to
provide for drainage of the base course
during spring thaw.
7. Determine the total road-structure thickness and cover requirements.

a. Enter Figure 9-54 for each layer of soil or aggregate with the following information:

- Design index.
Z Design CBR values for subgrade, select,
and subbase materials.
b. Determine the minimum cover thickness, in inches, for each layer of the road structure through Figure 9-54 and Table 9-19, page 9-71.

8. Determine the required percent compaction in terms of CE 55 for each layer from Table 9-20. 9. Draw the section of the bituminouspavement road structure. (See below.)


Adequate thickness above the subgrade
and above each layer together with adequate quality of the select material, subbase, and base courses to prevent detrimental shear deformation under traffic
and, when frost conditions are a factor,
to control or reduce the effects of frost
heave or permafrost degradation.

A stable, weather-resistant, wear-resistant, waterproof, nonslippery pavement.

## Design Steps.

1. Estimate the number of passes of each type of vehicle expected to use the road on a daily basis. 2. Select the proper road class based upon the traffic intensity from Table 9-8, page 9-59. 3. Determine the traffic category based upon the traffic-composition criteria given previously.

4. Determine the design index from Table
9-10, page 9-59, or 9-12, page 9-60.

5. Check soils and construction aggregates using standard criteria in Tables 5-9, page
5-12; 9-14, page 9-63; and 9-18, page 9-70. 6. Use Table 9-16 or 9-17, page 9-66, to determine compaction depth of the subgrade.

Example (Bituminous-Pavement Design):
5. Check soils and construction aggregate.

Design the most economical bituminous pavement for a 3-year design life capable of sustaining the following traffic:
a. Where can the CBR 30 material be used? Table 9-14, page 9-63, indicates this material can be used only as a select material (CBR 20) because the PI exceeds 5.

| Vehicle                                         |
|-------------------------------------------------|
| M998  HMMWV                               1,000 |

b. Where can the CBR 35 material be used? Table 9-14 indicates that this material can be used as a subbase with a CBR 30 design because of the percent passing the No. 10 sieve.

M35A2  2 1/2-ton  truck                                500 (dual axle) M113A3  (13  tons)                                            40 M1A1                                                               20

6. The required depth of subgrade compaction = 15 inches.

The soils data are
7. Determine the total thickness and cover requirements.

Subgrade:
CL material, PI = 12, W = 14 percent
Natural CBR = 5
Compaction at 90- to 95-percent CE 55, CBR = 7

a. From Figure 9-54, page 9-72, the required cover for each layer is determined for design index of 9.

Required     After Cover             Rounding
Layer
Compacted subgrade, CBR 7
B o r r o w :
CBR 30 at 90- to 95-percent CE 55
W = 8 percent, LL = 15, PI = 5
40 percent passing No. 10 sieve, 12
percent passing No. 20 sieve
18"                          18"
CBR 35 at 100- to 105-percent CE 55 W = 8 PERCENT, LL - 15, PI = 5
40 percent passing No. 10 sieve, 10 percent passing No. 20 sieve

Base:  GP material at CBR 50 (meets gradation)
b. From Table 9-19, page 9-71, the required minimum thickness for the base course and surface asphalt is determined for design index of 9.

## Solution:

1.  Total average daily traffic = 1,560 (given).

2.  Select road class E from Table 9-8, page 9-59, based upon average daily traffic of 1,560. 3.  Select traffic category VII based upon the presence of the M1A1 tank.

8. From Table 9-20, page 9-73, the required compaction is determined for each layer.

4.  Select design index 9 from Table 9-12, page 9-60.  Notice that the number of vehicles per day (20) in this table refers to the M1A1 only, since the M113A3 is considered as a Group 3 vehicle because of its weight.

9. Draw the section of the bituminouspavement road structure.

Special Considerations for Open Storage Areas.

In the design of open storage areas, consideration will be given to any special requirements necessary because of the use of a particular area.

In repair yards, for instance, the final-surface texture will be one that will promote quick drying and will not contribute to the easy loss of nuts, bolts, and tiny parts.

Mixtures in such areas will contain approximately 50 percent coarse aggregate. Areas subject to an appreciable amount of foot traffic will be designed to avoid the occurrence of free bituminous material on the surface.

## Special Design Considerations

Special design considerations include frost design, stabilized-base design, and geotextile design.

## Frost Design

Normally, frost effects are not considered as part of the design in TO road construction.

However, in the event that extremely severe host conditions exist or that frost design is directed, an outline of the frost-design procedure is included in Appendix G of this manual.

## Stabilized-Soil Design

The use of stabilized-soil layers (as described in Chapter 5 of this manual and in FM 5-410) within a road structure provides the opportunity to reduce the overall thickness required to support a given load. To design a road containing stabilized-soil layers requires the application of equivalency factors to a layer or layers of a conventionally designed pavement. To qualify for application of equivalency factors, the stabilized layer must meet appropriate strength and durability requirements.

An equivalency factor represents the number of inches of a conventional base or subbase which can be replaced by
1 inch of stabilized material. Equivalency factors are determined as shown on Table 9-21, page 9-76, for bituminous-stabilized materials and from Figures 9-55 and 9-56, page 9-76, for materials stabilized with Shoulders and Similar Areas. These areas are provided only for the purpose of minimizing damage to vehicles using them accidentally or in emergencies; therefore, they are not considered normal, vehicular traffic areas. Normally only shoulders for class A
roads will be paved. Others will be surfaced with soils selected for their stability in wet weather and will be compacted as required.

Dust and erosion control will be provided by means of vegetative cover, anchored mulch, coarse-graded aggregate, or liquid palliative. Shoulders will not block base-course drainage, particularly where frost conditions are a factor. Where paving of shoulders is deemed necessary, the shoulders will be designed as a class F
road or street.

known. The equivalency factors from Figure 9-55 are for subbase materials, and those from Figure 9-56 are for base materials.

Equivalency Factors
Material
Base
Subbase
All-bituminous concrete
1.15
2.30
GW, GP, GM, GC
1.00
2.00
SW, SP, SM, SC
--
1.50

Minimum Thickness. The minimum thickness requirement for a stabilized base or subbase is 4.0 inches. The minimum thickness requirements for an asphalt pavement are the same as shown for convention pavements in Table 9-19, page 9-71.

Application of Equivalency Factors. The use of equivalency factors requires that a road be designed to support the design-load conditions.

If using a stabilized base or subbase course, the thickness of a conventional base or subbase is divided by the equivalency factor for the applicable stabilized soil. The following are examples for the application of the equivalency factors:
cement, lime, or a combination of fly ash mixed with cement or lime. The selection of an equivalency factor from the tabulation is dependent upon the classification of the soil to be stabilized. The selection of an equivalency factor from Figures 9-55 and 9-
56 requires that the unconfined compressive strength (as determined according to the American Society of Testing and Materials Standatd (ASTM) D1633) be Example 1:
course is 4 inches/1.0 = 4.0 inches. The final section would be 2 inches of asphalt concrete and 9 inches of cement-stabilized, gravelly soil. The base-course thickness of
4.0 inches would also have been required due to the minimum thickness of the stabilized base. The subgrade still has an equivalent cover of 16 inches within the newly designed 2 inches of asphalt concrete and 9 inches of cement-stabilized, gravelly soil.

Assume an aggregate-surfaced road has been designed which requires a total thickness of 14 inches above the CBR 6 subgrade.

The minimum thickness of the 80
CBR base is 7 inches and the 15 CBR subbase is 7 inches. It is desired to replace the base and subbase with a lime-stabilized gravelly soil having an unconfined compression strength of 950 psi.

Example 3:
Solution:
Assume a conventional flexible pavement has been designed which requires 2 inches of asphalt-concrete surface, 4 inches of crushed stone base, and 6 inches of subbase. It is desired to construct an all-bituminous pavement.

Solution:
From Figure 9-55 the equivalency factor for the subbase is 2.20. From Figure 9-56, the equivalency factor for the base is 1.10.

Therefore, the thickness of the stabilized subbase is 7.0 inches/2.20 = 3.18 inches, and the thickness of the stabilized base is
7.0 inches/1.10 = 6.36 inches. However, since the minimum lift thickness is 4
inches, the stabilized subbase must be 4.0 inches instead of 3.18 inches. In addition, the stabilized base lift must be rounded up to the nearest full inch, so 6.36 inches is rounded up to 7 inches. Therefore, the final thickness is 7.0 inches of base + 4.0
inches of subbase = 11.0 inches of lime-stabilized gravel.

Example 2:
The equivalency factor from data in Table
9-21, for a base course is 1.15 and for a subbase is 2.30. The thickness of asphalt concrete required to replace the base is 4
inches/ 1.15 = 3.5 inches and the thickness of asphalt concrete required to replace the subbase is 6 inches/2.30 = 2.6 inches.

Therefore, the total thickness of the all-bituminous pavement is 2 + 3.5 + 2.6 or 8.1
inches, which would be reduced to 8.0 inches.

## Geotextiles

Assume a conventional flexible pavement has been designed which requires a total thickness of 16 inches above the subgrade.

The minimum thicknesses of the asphalt concrete and the base are 2 and 4 inches, respectively, and the thickness of the subbase is 10 inches.

It is desired to replace the base and subbase with a cement-stabilized, gravelly soil having an unconfined compressive strength of 890 psi.

The term geotextile refers to any permeable textile used with foundation, soil. rock, earth, or any other geotechnical, engineering-related material as an integral part of a human-made project, structure, or system. Geotextiles are commonly referred to as geofabrics, engineering fabrics, or just fabrics.

They serve four prlmary functions:
Solution:

Z Reinforcement. - Separation.
- Drainage. - Filtration.
From Figure 9-55, the equivalency factor for a subbase having an unconfined compressive strength of 890 is 2.0: and from Figure
9-56, the equivalency factor for the base is
1.0. Therefore, the thickness of the stabilized subbase is 10 inches/2.0 = 5.0 inches, and the thickness of the stabilized base In many situations, the use of these fabrics can replace soil, saving time, materials, and equipment costs.

In TO construction, the primary concern is with separating and reinforcing low load-bearing soils to reduce construction time.

established in previous sections has yet to be established. Nonetheless, Appendix H of this manual outlines a typical geotextile design procedure.

Note that Appendix H
describes only one design procedure, and the particular geotextile used in construction may require alterations to this procedure. Additional details on geotextiles and their use are in Chapter 11 of FM 5-410.

Geotextile design is an emerging technology.

As such, each geotextile manufacturer uses its own design procedure, and a general design procedure using the design criteria

## Appendix A - Metric Conversions

MULTIPLY
BY
TO OBTAIN
BY
TO OBTAIN
MULTIPLY
acre feet
acres
acres acres acres
acres
atmospheres
atmospheres
atmospheres atmospheres
43,560
43,560
4,047
1.562 x 10
5,645.38 4,840
76.0
29.92
33.90
14.70
cubic feet
square feet
square meters square miles square varas square yards
cm of mercury inches of mercury
feet of water
pounds per sq in
barrels
board feet
BTU BTU BTU
BTU per min BTU per min BTU per min
bushels
31.5
144 sq in x 1 in
0.2520
778.2 2.928 x 10 0.02356 0.01757
17.57 1.244
gallons cubic inches
kilogram calories
foot pounds
kilowatt hours horsepower
kilowatts
watts
cubic feet
1
0.01 0.01 0.3937 0.01
393.7
10 1 x 10
7.233 x 10
0.01316
0.4461 136.0
27.85
0.1934 0.6 0.7854 4 ft x 4 ft x 1 ft 8 ft x 4 ft x 4 ft
6.102 x 10
1 x 10
2.642 x 10
10
centares
centigrams centiliters centimeters centimeters centimeters
centimeters
centimeter grams centimeter grams cm of mercury
cm of mercury cm of mercury cm of mercury
cm of mercury cm per second circular mils
cord feet
cords cubic cm
cubic cm
cubic cm cubic cm cubic feet
cubic feet cubic feet cubic feet cubic feet cubic feet cubic feet per min cubic feet per min cubic feet per min cubic feet per min cubic inches
cubic inches
cubic inches
cubic meters
cubic meters cubic meters cubic meters cubic yards
2.832 x 10 1,728
0.02832 0.03704
7.481 28.32
472.0
0.1247 0.4720 62.4
16.39
5.787 x 10 0.01732 1 x 10
35.31
1.308
264.2 27
square meters grams
liters inches meters mils millimeters
meter kilograms pound feet
atmospheres
feet of water
kg of sq meters pounds per sq ft pounds per sq in meters per mm square mils cubic feet cubic feet cubic inches
cubic meters
gallons
liters cubic cm
cubic inches cubic meters cubic yards gallons
liters cubic cm per sec gallons per sec liters per sec lb of water per min cubic cm cubic feet quarts (liquid)
cubic cm cubic feet cubic yards gallons
cubic feet
cubic yards
cubic yards
cubic yards per min cubic yards per min
0.7646
202.0
0.45
3.367
cubic meters
gallons
cubic feet per sec gallons per sec
decigrams deciliters
decimeters
degrees (angle) degrees (angle)
degrees (angle) dekagrams dekaliters dekameters
drams drams
0.1 0.1
0.1
60 0.01745 3,600
10
10 10
1.772
0.0625
grams
liters meters
minutes radians seconds grams
liters
meters
grams ounces
9.486 x 10
BTU
ergs
6 03048 0.36 0333 04335 0.5080 0.01667
0.01136
1.097
0.5921
18.29
0.6818
1 1.286 x 10
1.356 x 10 5.050 x 10
3.241 x 10
3.766 x 10
1.286 x 10
3.030 x 10 3.241 x 10
2.260 x 10
40
fathoms feet feet feet feet of water
feet per min feet per min feet per min feet per sec feet per sec feet per sec feet per sec feet per 100 feet foot pounds foot pounds foot pounds foot pounds
foot pounds
foot pounds per min foot pounds per min foot pounds per min
foot pounds per min
furlongs
feet
meters varas yards lb per sq in cm per sq in feet per sec
miles per hour
km per hour
knots per hour
meters per min miles per hour percent grade BTU
ergs
horsepower hours kilogram calories kilowatt hours
BTU per min horsepower kg calories per min
kilowatts
rods
3,785
0.1337
231
3.785 x 10 4,951 x 10
2.228 x 10
0.1183
1
0.06480 0.04167 980.7
15.43
10
gallons gallons gallons gallons gallons
gallons per min gills grains (troy) grains (troy) grains (troy) grams grams grams
grams
grams grams grams gram calories
cubic cm
cubic feet
cubic inches cubic meters cubic yards cubic feet per sec
liters grains (av) grams penny weights (troy) dynes grains (troy)
kilograms milligrams
ounces
ounces (troy)
pounds
BTU
10
0.03527 0.03215
2.205 x 10
3.968 x 10

## Metric Conversions (Continued)

TO OBTAIN
MULTIPLY
BY
TO OBTAIN
MULTIPLY
BY
10
2.344 x 10
kilogram calories kilogram meters
pounds per inch
pounds per cu ft
5.600 x 10
62.43
gram centimeters gram centimeters
grams per cm
grams per cu cm
kilometers per hour kilowatts
kilowatts
kilowatts
kilowatt hours kilowatt hours
knots
knots
links (engineer's) links (surveyor's) liters liters
liters
liters per minute liters per minute
acres
square feet grams
liters meters watts
BTU per min
ft pounds per min ft pounds per sec
horsepower (metric) kg calories per min kilowatts
watts
2.471
1.076 X 10 100
100
100
100
42.44 33,000
550
1.014
10.70
0.7457 745.7
hectares
hectares hectograms
hectoliters
hectometers hectowatts
horsepwer horsepower horsepower
horsepower horsepower horsepower horsepower
2.540
10
0.03
0.03342
1.133
70.73 0.002458
0.07355
centimeters
mils
varas
atmospheres feet of water pounds per sq ft atmospheres inches of mercury
ounces per sq in pounds per sq ft
pounds per sq in
0.5781
5.204
0.03613
inches inches inches inches
inches of mercury inches of mercury inches of water
inches of water
inches of water inches of water inches of water
9.486 x 10 10 0.7376
BTU
ergs
foot pounds kilogram calories
kilogram meters watt hours
2.390 x 10
0.1020 2.778 x 10
joules joules joules
joules
joules
joules
meters meters meters
meters meters meters microns miles miles
miles
miles per hour miles per hour
miles per hour
milliers milligrams
milliliters millimeters millimeters millimeters mils mils minutes (angle)
minutes (angle)
myriagrams myriameters
myriawatts
nautical miles nautical miles
ounces
ounces ounces
ounces
ounces (fluid) ounces (troy) ounces (troy)
ounces (troy)
ounces (troy)
980,665
1 x 10
2.2046
1.102 x 10
3.968
3,088
1.588 x 10 1.162 x 10
0.06972
9.302 x 10 9.807 x 10
1 x 10
0.06243 9.678 x 10
3.281 x 10
2.886 x 10 0.2048
1.422 x 10
10
perches (masonry)
pints (dry)
pints (liquid) pounds
dynes
grams
pounds
tons (short)
BTU
foot pounds horsepower hours kilowatt hours kilowatts
BTU
ergs
grams per cu cm pounds per cu ft
atmospheres
feet of water
inches of mercury pounds per sq ft
pounds per sq in
liters
centimeters
feet
meters miles
10
3,281
10
0.6214

kilograms
kilograms
kilograms
kilograms
kilogram calories
kilogram calories
kilogram calories
kilogram calories
kilogram calories per min
kilogram meters
kilogram meters
kilograms per cubic meter
kilograms per cubic meter
kilograms per sq meter
kilograms per sq meter
kilograms per sq meter
kilograms per sq meter
kilograms per sq meter
kiloliters
kilometers
kilometers
kilometers
kilometers

0.5396
56.92
4.425 x 10
1.341
3,415
2.655 x 10
1.853 1.152
knots per hour
BTU per min
ft pounds per min
horsepower
BTU
foot pounds
kilometers per hour miles per hour
12 7.92 10
0.2642
1.057
5.885 x 10
4.403 x 10
inches
inches
cubic centimeters gallons
quarts (liquid)
cubic feet per sec gallons per sec
100
3.2808
39.37
10
10
1.0936
10
5,280
1.6093
1,760 1.467
1.6093
0.8684
0.1 0.03937 39.37 0.002540
10
2.909 x 10
60
10 10
10
centimeters feet
inches
kilometers
millimeters yards meters feet kilometers
yards
feet per second kilometers per hour knots per hour
kilograms
grams liters centimeters inches
mils
centimeters inches radians
seconds (angle) kilograms
kilometers
kilowatts
1.152
2.027
miles
yards
8
437.5 28.35 0.0625
1.805
480
31.10
20
0.08333
drams grains
grams
pounds cubic inches grams (troy) grams pennyweights (troy)
pounds (troy)
24.75
33.60
28.87
444,823
cubic feet cubic inches
cubic inches
dynes

## Metric Conversions (Continued)

MULTIPLY
BY
TO OBTAIN
MULTIPLY
BY
TO OBTAIN
453.6
16
32.17
1.356 x 10
13,825
0.1383 0.01602
27.68 0.1198
16.02
27.68
1.488
0.01602 4.882
0.06804 2.307 2.038
703.1
144
pounds
pounds
pounds pound feet
pound feet
pounds feet pounds of water pounds of water pounds of water
pounds per cubic foot pounds per cubic inch
pounds per foot pounds per square foot
pounds per square foot pounds per square inch pounds per square inch pounds per square inch pounds per square inch pounds per square inch
grams
ounces
poundals
centimeter dynes centimeter grams
meter kilograms
cubic feet cubic inches
gallons
kg per cubic meter
grams per cu cm
kilograms per meter
feet of water
kilograms per sq meter atmospheres
feet of water
inches of mercury kg per square meter pounds per sq ft
quadrants (angle) quadrants (angle) quadrants (angle) quarts (dry) quarts (liquid)
degrees
minutes radians
cubic inches cubic inches
90
5,400
1.571
67.20
57.75
radians radians radians
reams revolutions revolutions revolutions revolutions per minute
revolutions per minute revolutions per minute
revolutions per min per min
revolutions per min per min revolutions per min per min
revolutions per second
revolutions per second
rods
degrees
minutes
quadrants sheets
degrees
quadrants
radians
degrees per second
radians per sec
rev per second radians per sec per sec
rev per min per sec rev per sec per sec
degrees per second
radians per second
feet
57.30
3,438
0.0637
500
360 4
6,283
6 0.1047 0.01667
1.745 x 10 0.01667
2.778 x 10
360
6.283
16.5
radians square inches square millimeters
acres square meters square miles
square varas square yards square centimeters square feet acres square feet
square meters square miles square yards acres square feet
square miles
seconds (angle) square centimeters
square centimeters square feet square feel square feet
square feet square feet square inches square inches square kilometers square kilometers square kilometers square kilometers square kilometers square meters square meters square meters
4.848 x 10 0.1550
100
2.296 x 10 0.09290 3.587 x 10
0.1296
0.111 6.452 6,944 x 10 247.1
10.76 x 10 1 x 10
0.3861
1.196 x 10
2.47 x 10
10.764
3.861 x 10
square yards
acres
square feet square kilometers square varas square yards acres
square feet square meters
square miles
square varas hemispheres liters
1.196
640
27.88 x 10 2.590 3,613,040.45 3.098 x 10
2.066 x 10
9
0.8361 3.228 x 10
1.1664
0.1592
10
square meters
square miles
square miles square miles square miles square miles
square yards square yards
square yards square yards
square yards steradians steres
1 1.8 1
0.555
1,016
2,240
1 0
absolute temp (deg C temperature (deg F)
absolute temp (deg F)
temperature (deg C)
kilograms
pounds kilograms pounds kilograms pounds kg per sq meter
pounds per sq in kg per sq meter
pounds per sq in
2,205 907.2
2,000
9,765
13.89 1.406 x 10
2,000
temperture (deg C) + 273 temperature (deg C) + 17.8
temperature (deg F) + 460
temperature (deg F) - 32 tons (long) tons (long)
tons (metric) tons (metric)
term (short) tons (short) tons (short) per sq ft
tons (short) per sq ft tons (short) per sq ft
tons (short) per sq in
2.7777
feet
varas
BTU per min ergs per second
foot pounds per min
horsepower kilowatts
BTU
hours
0.05692
10
44.26
1.341 x 10
10
3.415
168
watts
watts watts watts watts
watt hours
weeks
centimeters feet
inches meters
91.44 3
36
0.9144
yards
yards yards yards

## Metric Conversions (Continued) Appendix B - Geometric Formulas

(6) Regular polygons. The area of any regular polygon (all sides equal, all angles equal) is equal to the product of the square of the lengths of one side and the factors. Example problem: Area of a regular octagon having 6-inch sides is 6 x 6 x 4.828, or 173.81 square inches. See factors in table.

## Geometric Formulas (Continued) Geometric Formulas (Continued) Geometric Formulas (Continued) Appendix C Hydrologic And Hydraulic Tables And Curves Precipitation  Tables

These curves are computed from Horton's equation given in Chapter 6, using a retardance coefficient in n = 0.04 and hydraulic gradient S = 1 percent.

Table C-1, page C-2, provides local data for use in designing drainage systems as discussed in Chapter 6.

## Hydraulic Characteristics Of Selected Drainage Channels Hydrologic Supply Curves For Overland Flow

Tables C-2 through C-10, pages C-14
through C-22, present commonly used ditch sections, with cross-section areas and hydraulic radius, to facilitate selection of ditch size and shape.

Figures C-1 through C-7, pages C-7 through C-13, represent the peak runoff rates from individual storm events of various durations, all of which have the same average frequency of occurrence.

Note: L = effective length of overland or channel flow, in feet.
      tc = critical duration of supply, in minutes, assuming surface
           storage as negligible.
          = rate of supply, in inches per hour.

## Appendix D Cone Index Requirements Fine-Grained Soils

Tracked Vehicles
Vehicle
Weight
Vehicle Description
(kips)
Amphibious vehicles
18
7
20
49
19
45
Carrier, cargo, amphibious,
10.9
tracked, M116
Landing vehicle, tracked,
97.5
command, M5(LVTP5A1(CMD))
Landing vehicle, tracked,
87.8
personnel, M5 (LVTP5A1)
Armored bulldozers
Bulldozer, earthmoving tank,
116.0
23
53
tank-mtd, M9 (tank, combat,
105-mm gun, M60, and M60A1)
Tractor, armored, combat
35.6
18
41
earthmover (ACE), M9

## Notes:

1. Items listed include selected self-propelled vehicles as of January 1993. Certain items in final development or undergoing field testing have been included where the type of classification is pending. 2. The VCIs have been calculated from the formulas, curves, and tables in NRMM. The vehicle weight was based on normal design loads or combat weights, equipment, crosscountry tire pressures, and crews as the conditions would be under full operational deployment in typical off-road movements.

Trucks which could operate at lower tire pressures would generate slightly lower VCI values with increased tire deflection.

3. Amphibious vehicles and engineer tractors have grousers greater than 1 1/2 inches;
all other tracked vehicles have grousers less than 1 1/2 inches.

4. One kip equals 1,000 pounds (US customary).

## Tracked Vehicles (Continued)

Vehicle
Weight
Vehicle Description
(kips)
Combat vehicles
35.8
98.0
58.5 53.2 46.0 53.0 53.0 46.9
27.7 47.1
99.0 99.0
104.0
105.0 105.0 104.0 106.0
Armored reconnaissance
airborne assault vehicle
(General Sheridan), M551
Howitzer, heavy, selfpropelled, full- tracked, 8-in, M55 (T108)
Howitzer, heavy, selfpropelled, 8-in, M110 (T236E1)
Howitzer, medium, selfpropelled, 155-mm, M109 (T196E1)
Howitzer, light, self-propelled,
full-tracked, 105-mm, M37
Howitzer, light, self-propelled,
full-tracked, 105-mm,
M52 M52A1
Howitzer, light, self-propelled,
105-mm, M108
LAV-25, 8x8, light, armored
vehicle
Mortar, infantry, selfpropelled,
full-tracked,
107-mm (4.2-in), M84
Tank, combat, full-tracked,
90-mm gun,
M48 M48C
M48A1 M48A2
M48A2C M48A3 (M48A1E2) M48A5
Tank, combat, full-tracked,
105-mm gun,
M60
M60A1 M60A3
110.0 116.0
110.0

## D-2 Cone Index Requirements

35
15
47
20
47
20
57
25
58
N/A
46
46 54
N/A N/A
N/A
72
32
46
N/A
47 47 49
49 49 49
50
20
20 21 21 21 21 22 21 22 20
48
51 46

## Tracked Vehicles (Continued)

Vehicle
Weight
Vehicle Description
(kips)
Combat vehicles continued
115.0
23
125.0
25
Tank, combat, full-tracked,
120-mm gun,
M l
M1A1 M 1A2
140.0
28
115.0
N/A
54
58 64
54
Vehicle, combat engineer,
full-tracked, 165-mm gun, M729 (basic M60A1 tank)
A r m o r e d  v e h i c l e  b r i d g e s
N/A
49
96.0
N/A
128.0
65
86.3
36
15
115.9
51
22
Launcher, M48 tank chassis,
transporting
Launcher, M48 tank chassis,
transporting, with bridge,
armored vehicle launched,
scissoring type, class 60,
60-ft
Launcher, M60A1 chassis,
transporting
Launcher, M60A1 chassis,
transporting with bridge,
armored vehicle launched,
scissoring type, class 60, 60-ft
Carriers
37
28.0
N/A
40 40
17 17
23.9 24.4
Carrier, cargo, tracked,
6-on, M548
Carrier, command post, light,
tracked,
M577
M577A1
Carrier, personnel, fulltracked, armored,
M113
M113A1
M113A2 M113A3
48
49
49
49
N/A
N/A N/A N/A
22.6 23.4 23.4
23.6

## Tracked Vehicles (Continued)

Vehicle
Weight
Vehicle Description
(kips)
Carriers (continued)
vehicle,
Infantry fighting
50.2 66.0 54,2
M2A1 M2A2
Multiple Launch
Rocket System
Recovery vehicles
112.0
Recovery vehicle,
full-
54.0
tracked, medium, M88
Recovery vehicle, fulltracked, light, armored, M578
Wheeled Vehicles
Trucks
3.1
7.5 9.6 9.3
utility
17.2 19.2
Truck, utility, 1/4-ton,
4x4, M151
Truck, utility, 1 1/4-ton,
4x4 M998 (HMMWV)
Truck, cargo, 1 1/4-ton,
6x6, M561
Truck, cargo, 1 3/4-ton,
4x4, M 1028 commercial
cargo vehicle (CUCV)
Truck, cargo, 2 1/2-ton,
6x6, M34
Truck, cargo, 2 1/2-ton,
6x6, M35A 1
32.5
43.4
Truck, cargo, 5-ton, 6x6
M923
Truck, cargo, 8-ton, 4x4
M520
Truck, cargo, 10-ton, 6x6
M125
M125A1
49.5
49.5
60.4
35.8
Truck, cargo, 10-ton, 8x8
M977
Truck, cargo, 5-ton, 6x6
M 1084

## D-4 Cone Index Requirements

35 37 35
15 16 15
50
21
49
21
44
19
47
20
44
19 31
70
27
61
59
26
68
30
97
43
84 84 79
37 37
36
57
25

## Wheeled Vehicles (Continued)

Vehicle
Weigh t
Vehicle Description
(kips)
Trucks (continued)
l/2-ton,
21.8
25
57
1 /2-ton,
19.2
28
64
Truck, cargo, 2
4x4, M1078
Truck, dump, 2
6x6, M47
Truck, dump, 5-ton, 6x6,
72 72
68
32
32 30
32.7 32.7 32.7
48 48
21 21
17.8
17.8
21 22
22
48 50 50 76
28.9 30.2 30.2 25.1
N/A
65
21.0
N/A
62
20.4
N/A
63
N/A
19.8
73
44.8
32
76
N/A
34.4
77
34
86.6
M51
M51A2 M929
Truck, tractor, 5-ton, 6x6
M52 (w/o payload) M52A1 (w/o payload)
Truck, tractor, 10-ton, 6x6
M123 (w/o payload) M123C (w/o payload)
M123D (w/o payload)
Truck, van, expansible,
2 1/2-ton, 6x6, M292
Truck, van, shop, 2 1/2-
ton, 6x6, M109A1
Truck, van, shop, 2 1/2-
ton, 6x6, M220
Truck, wrecker, crane,
2 1/2-ton, 6x6, M108
Truck, tractor, wrecker,
medium, 5-ton, 6x6, M246
(w/ payload)
Truck, wrecker, medium,
5-ton, 6x6, M543
Palletized Loading System,
10 x 10

## Appendix E Soil-Trafficability Test Set

proper places in the carrying case in Figure E-1, SC-6635-98-CL-E02-HR gives component listings and stock numbers.

## Cone Penetrometer

The cone penetrometer is shown in Figure E-2, page E-2.

It consists of a 30-degree cone with a 1/2-inch-square base area, a steel shaft 19 inches long and 3/8 inch in diameter, a proving ring, a micrometer dial, and a handle.

Use of the Cone Penetrometer Inspect and adjust the cone penetrometer prior to use. Using an operator's assistant Trafficability measurements are made with the soil-trafficability test set. This set consists of one canvas carrying case, one cone penetrometer with 3/8-inch steel and 5/8- inch aluminum shafts and a 0.5-squareinch cone, one soil sampler, remolding equipment (which includes a 3/8-inch steel shaft and a 0.2-square-inch cone, a 5/8- inch steel shaft with foot and handle, a 2
1/2-pound hammer, and a cylinder and base with pin), and a bag of hand tools
(which includes one combination spanner wrench and 1 /4-inch screwdriver; two openend wrenches, 1/2 by 9/16; one 6-inch Stillson wrench; one 3/16-inch Allen wrench; and one 2-inch screwdriver with a
1/8-inch bit). The items are shown in their Operation. Operate the penetrometer as follows:
1. Place one hand over the other on the handle, palms down, and approximately at right angles as shown in Figure E-3. This minimizes eccentric loading of the proving ring and helps keep the shaft vertical.

2. Apply force until slow, steady downward movement occurs.
3. Take a dial reading just as the base of the cone becomes flush with the ground surface. To do this, watch the cone descend until an instant before the cone base is expected to be flush with the ground surface, then immediately shift the vision to the dial face. Continue the slow, steady, downward movement and take successive dial readings which measurements can be made and recorded and usually diminishes the likelihood of errors.

Inspection. Inspect the penetrometer before using it to make sure that all nuts, bolts, and joints are tight and that the dial-gage stem contacts the proving-ring bearing block.

Zeroing. Allow the penetrometer to hang vertically from its handle, and rotate the dial face until 0 is under the needle. When the instrutment is kept vertical between the fingertips and allowed to rest on its cone, the dial will register about 2 to 4 pounds the total weight of the instrumentor 4 to
8 on the dial.

## E-2 Soil Trafficability Test Set

ques of operation.

He should practice penetration, observed by a qualified instructor, until he becomes familiar with the techniques of operation. The trainee should then make 50 sets of readings, using an assistant to record them. The average CIs obtained by a trainee should be compared to the standard. If the trainee's readings deviate widely, the causes for the deviations should be sought and corrected.

at appropriate 6-inch intervals to a depth of
18 inches, If it is necessary to stop the downward progression of the cone penetrometer for any reason, progress may be resumed with no adverse effects on the cone penetrometer readings. Progression should be stopped between depths so that the next reading is taken only after downward progression has resumed. For example, when only one person is on the trafficability reconnaissance, it may be convenient to make two cone penetrometer readings, stop the penetration to record the readings, resume the penetration to obtain two additional readings, then stop to record.

Precautions.

Observe the following precautions when operating a penetrometer:

- Keep the instrument vertical.
- Do not attempt to take readings higher
than the capacity of the dial (300). This may overstress the proving ring.
- If dial capacity is exceeded at less than
18 inches of penetration, make another
penetration nearby. The cone may be striking an isolated rock fragment or
other object.
- Withdraw the instrument by the shaft,
never by the ring or the handle. Pulling
the handle may stretch the proving ring.
In a uniform area, a 5-percent deviation is wide. The most probable cause of error is carelessness in determining the proper depth.

The rate of progression recommended is such that four readings (surface,
6, 12, and 18 inches) can be measured in
15 seconds during a continuous penetration in soft soil. Slower or faster penetration rates will reflect lower or higher values, respectively, but the discrepancies will not be large. The CI is also insignificantly affected by the variation in the rate of penetration for the same operator or between experienced operators. However, if deviations persist, check the possibility of cone-penetrometer mechanical imperfections, Inspect the dial face to ensure that its position has not shifted around the dial's shaft and that the needle is not sticking or has not slipped on its shaft. Any of these conditions could cause an improper zero setting. Secondly, inspect the proving ring. A damaged or overstressed ring might require recalibration. Finally, check to ensure the Instrument was properly zeroed.

The micrometer dial stem may not have been in good contact with the proving-ring bearing block when the instrument was zeroed.

## Care And Adjustment Of The Penetrometer

- Read the CI only at the proper depth. If
readings are made as little as 1/4 inch
from the proper depth and recorded as
being at the proper depth, an average of
such readings will not accurately reflect
the average strength. Carelessness in
making proper depth determinations is
probably the greatest source of error in using the penetrometer.

## Training Penetrometer Operators

Keep the penetrometer free from dirt and rust and keep all parts tight. Frequently check the instrument and rezero, if necessary. Ensure no grit is caught between the stem of the dial and the lower mounting block.

Train operators in areas that have uniform soil conditions. The instructor should take approximately 50 sets of readings equally spaced over the area. The average CI for 6- inch layers should be computed and used as standards or references. The trainee should be instructed in all proper techni-
Dial Care. The micrometer dial is a sensitive instrument that should be protected against water and rough use. Never immerse it in water, and wipe it dry as soon

5. Zero the dial by rotating its face so that
0 is under the needle.
as possible after use in rainy weather. When the dial is transported by truck, wrap it in paper or cloth.

6. Add the load in 10-pound increments
up to 150 pounds. Mark or note the
needle's position on the dial after the addition of each load increment. Any of the following loading methods may be used:
- Add deadweights to the top of the ring
assembly. If a plate is used to hold the
weights, its weight should be considered in the first 10-pound load.
Bearing-Block Adjustment. If either or both bearing blocks become loosened and moved, adjust them so that they lie on the same diameter of the ring. Retighten them and recalibrate the proving ring. Do not calibrate while on reconnaissance. Instead, note all readings made in the field after bearing blocks have been removed and correct them according to the calibration made later.

Z Use any of the load machines commonly
used in laboratory work to apply the
load.
Cone Replacement.

Considerable use of the same cone may result in a rounding of its point, but it will not affect the accuracy of the instrument, However, if the base of the cone has had excessive wear or is deformed by hard use, replace the cone.

Z Place the ring assembly on a set of platform scales. Apply the load increments with a jack and measure them with the
platform scales.
7. Remove the load in 10-pound increments, noting the position of the needle
after the removal of each increment.
8. Make the load run at least twice, using
the average of the needle position for each
increment as the final point.
Proving-Ring Recalibration. The calibration will remain true for the life of the instrument unless the bearing blocks are moved or the ring is overstressed (deformed by a hard knock or subjected to extreme changes in temperature or other unusual strains).

If the ring needs recalibration, complete the following steps:

1. Remove the handle and shaft,
9. Expect some variation in needle position; it will not be significant.
2. Place the lower mounting block of the
ring assembly on a smooth, horizontal surface.
10. Establish 10-pound intervals on the
dial face and mark them 20, 30, 40, so on,
to 300. Each interval should be subdivided separately because the arcs for various 10-
pound intervals are not necessarily the
same.
3. Check the bearing-block alignment and tightness.

Both blocks should be on the same diameter of the ring. Use a drafting triangle or a carpenter's square for this operation. The bolts should be snug.

NOTE: If the instrument cannot be
calibrated or the proving ring is severely
damaged, the instrument will need to be
turned in for repair.

## Soil Sampler

A piston-type soil sampler, as shown in Figure E-4, is used to extract soil samples for remolding tests.

4. Ensure that the stem of the dial bears firmly on the lower bearing block. Ensure that the dial arm has sufficient travel available for the full range of motion (approximately 1/10-inch deflection) of the proving ring. The dial can be moved up or down by adjusting the two nuts on the threaded stud that holds the gage in position. Both nuts should be tight when in final position.

## Operation

The soil sampler is used in the following way:

## Care

It is essential to keep the inside of the sampling tube, the piston ring, and the leather washer clean.

After 5 to 25 samplings,
1. Loosen the knurled handle of the soil sampler so the piston rod will move freely.

Hold the sampler firmly in both hands and force it into the soil vertically (Figure E-5). Do not twist the sampler while pushing it into the soil. Sometimes two people are needed to force the sampler into firm soils.

depending upon the type of soil, complete the following cleaning procedures:
2. After locking the piston rod by turning the knurled handle, twist the sampler slightly and withdraw.

1. Immerse the tube first in water and then in fuel oil. Work the piston up and down five or six times in each liquid.

3. Deposit the sample directly into the remolding cylinder.

2. Wipe off the excess fuel oil, and squirt light machine oil into the tube.

Figure E-6, page E-6, for using the sampler shows the technique in a prone position.

3. If the sampler becomes stiff and hard to work, remove the tube, disassemble and thoroughly clean the piston, and oil the leather washer.

Tube walls and cutting edges are soft and should be handled with care. The cutting edges will require sharpening from time to time.

Z A steel cylinder approximately 2 inches
in diameter and 8 inches long, mounted
on an aluminum base.

## Adjustment

- A 2 1/2-pound steel drop hammer sliding on an 18-inch steel shaft with a handle.
Z A cone penetrometer
Adjust the piston-rod length to keep the face of the piston flush with the cutting edge of the tube when the piston-rod handle (disk) is fully depressed. To do this, loosen the setscrew on the handle, screw the handle up or down to the correct position, and retighten the setscrew.

## Remolding Test

The equipment for the remolding test, shown in detail in Figure E-7 and in use in Figures E-8 through E-11, pages E-7 through E-9, consists of the following:
A cone penetrometer may be equipped with an aluminum shaft (5/8-inch in diameter) or a steel shaft (3/8-inch in diameter) with a 0.5-square-inch cone (for fine-grained soils) or a more slender steel shaft with a
0.2-square-inch cone (for remoldable sands). The penetrometer is used to measure soil strength in the cylinder before and after remolding. The sampler (Figure

## E-6 Soil Trafficability Test Set

cylinder with shaft.

push it to the bottom of the the foot of the drop-hammer
2. Measure the strength with the penetrometer (steel shaft) by taking CI readings as the base of the cone enters the surface of the soil sample and at each successive inch, to a depth of 4 inches, as shown in Figure E-10, page E-9,
3. Apply 100 blows with the drop hammer falling 12 inches as shown in Figure E-11, page E-9.

4. Measure the remolded strength from the surface to the 4-inch depth at 1 -inch increments, as was done before remolding as shown in Figure E-10.

NOTE: Some samples are so hard they
cannot be penetrated the full 4 inches.
In such cases, the full dial capacity (300)
is recorded for each inch below the last
reading obtained.

To find the remolding index, take the sum
of the five CI readings after remolding and
divide by the sum of the five readings
before remolding.

## Test Procedure For Remoldable Sands

E-4, page E-5) is used to obtain the soil sample from the critical layer and place it in the remolding cylinder.

Test Procedure for Fine-Grained Soils The following remolding test is performed for fine-grained soils:
1. Take a sample from the critical layer with the sampler as shown in Figure E-8, eject it directly into the remolding cylinder as shown in Figure E-9, page E-8, and The test procedure for remoldable sands is generally the same as that for fine-grained soils. However, the CI measurements are made with the slender shaft and 0.2-squareinch cone, and the sample is remolded by placing a rubber stopper in the top of the remolding tube and dropping it (along with the cylinder and base) 25 times from a height of 6 inches onto a firm surface, such as a piece of timber. Some remoldable sands with a large amount of fines (more than 12 but less than 50 percent) react very much like fine-grained soil, When testing a remoldable sand with a large amount of fines, run both the fine grains and remoldable sands tests, and use the lower remolding index.

Continue to use the more critical test throughout the area.

## Appendix F Curve Tables Functions Of A1-Degree Curve Corrections For Tangents And Distances

Complete the following steps to determine the degree of curvature for all curves other than the 1-degree curve:
1. Determine the value corresponding to the given intersection angle from Table F-1.

The long chords (C), middle ordinates (M), externals (E), and tangent distances (T) in Table F-1, pages F-2 through F-30, are for a 1-degree curve, based on the arc definition (5,729.578-foot radius). To find the corresponding functions of any other curve, divide the tabular values by the degree of curvature.

2. Divide this value by the given degree of curvature.

3. Add the correction derived from Table F-2, pages F-30 and F-31.

## Appendix G Frost Design For Roads Frost-Area Considerations

grade soils. Soils are listed in approximate order of decreasing bearing capability during periods of thaw.

## Required Thickness

Where frost-susceptible subgrades are encountered, the section thickness required will be determined according to the reducedsubgrade-strength method. The reducedsubgrade-strength method requires the use of frost-area soil-support indexes listed in Table G-2, page G-2, and strength curves shown in Figure G-1, page G-2. The In areas where frost effects have an impact on the design of roads, additional considerations concerning thicknesses and required layers in the road structure must be addressed. The specific areas where frost has an impact on the design are discussed in the following paragraphs: however, a more detailed discussion of frost effects is presented in Special Report 83-27. For frostdesign purposes, soils have been divided into seven groups as shown in Table G-1. Only the NFS group is suitable for a base course. NFS, S1, S2, F1, or F2 soils may be used for a subbase course, and any of the six groups may be encountered as subcurve, and then moving vertically downward to determine the design thickness in inches.

## Required Layers In A Road Section

When frost is a consideration, the road section should consist of a series of layers that will ensure the stability of the system, particularly during thaw periods. The layered system in the aggregate fill may consist of a wearing surface of fine-crushed stone, a coarse-graded base course, and a wellgraded subbase of sand or gravelly sand as shown in the following example:
required thickness is determined by comparing the natural subgrade CBR to the frostarea soil-support index associated to the relevant first group. If the natural subgrade CBR is less than the frost-area soilsupport index then the CBR value governs the design, and the thickness is determined from Figure G-2.

If the natural subgrade CBR is greater than the soil-support index, then Figure G-1 is used. The required thickness is determined by entering Figure G-1 at the zontally to correct design index moving horiintersect the relevant frost-group

## Compaction

To ensure the stability of the wearing surface, the width of the base course and subbase should exceed the final desired surface width by a minimum of 1 foot on each side.

## Wearing Surface

The subgrade should be compacted to provide uniformity of conditions and a firm working platform for placement and compaction of the subbase. However, compaction of the subgrade will not change its frostarea soil-support index because frost action will cause the subgrade to revert to a weaker state.

The wearing surface contains fines to provide stability in the aggregate surface. The presence of fines helps the layer's compaction characteristics and helps to provide a relatively smooth riding surface. Its thickness will vary between 4 and 6 inches.

## Thickness Of Base Course And Filter Layer Base Course

The relative thicknesses of the base course and filter layer are variable and should be based on the required cover (minimum of 4
inches] and economic considerations.

## Frost-Area Design Steps

The coarse-graded base course is important in providing drainage of the granular fill. It is also important that this material be NFS so that it retains its strength during spring thaw.

## Subbase

Steps 1 through 5 are the same as for regular aggregate-surfaced roads. (Refer to Chapter 9, page 9-66.)
6. Determine the applicable frost group for the subgrade type from Table G-1, page G-1.

7. Determine the frost-area soil-support index from Table G-2, page G-4, based on the applicable frost group.

The well-graded sand subbase is used for additional bearing capacity over the frostsusceptible subgrade and as a filter layer between the coarse-graded base course and the subgrade.

This process prevents the migration of the subgrade into the voids in the coarser material during periods of reduced subgrade strength. The material must therefore meet standard filter criteria.

8. Determine the required road-structure thickness. First, compare the natural subgrade CBR to the frost-area soil-support index.

a, If the natural subgrade CBR is less than the frost-area soil-support index, then the CBR value governs the design, and the thickness is determined from Figure G-2, page G-4, as in nonfrost design.

b. If the natural subgrade CBR is greater than the frost-area soil-support index, then Figure G-1, page G-2, is used.

The required thickness is determined by entering Figure G-1 at the design index, moving horizontally to intersect the frost-group curve, and then moving vertically downward to determine the thickness in inches.

The sand subbase must be either NFS, S1, or S2. The filter layer may or may not be necesary depending upon the type of subgrade material.

If the subgrade consists principally of gravel or sand, the filter layer may not be necessary and may be replaced by additional base course material, if the gradation of the base course is such that it meets filter criteria. However, for finergrained soils, the filter layer will be necessary. If a geotextile is used, the sand subbase or filter layer may be omitted because the fabric will be placed directly on the subgrade and will act as a filter. If select materials are used, they must be either NFS, S1, S2, F1, or F2 from Table G-1, page G-1.

9. Determine the required compaction densities for each layer from Table 9-12, page 9-
63.

10. Draw the section of the aggregate road
2. The material should meet gradation restructure.

quirements.

NOTES:
                                       3. After all possible design sections are
                                       determined, the final section used should
1. All layer depths should be rounded up
                                       be determined on the basis of economic
to the next full inch for construction pur-
                                       analysis.
poses.

## Example (Frost-Area Design):

6. From Table G-1, page G-1, the subgrade frost group is F3 based on it being a clay (CL) material.

An aggregate-surfaced road in a frost area is to be used for one year. The road will be subject to
7. Select frost-area support-index of 3.5 from Table G-1, based on frost group F3.

Vehicles
Average Daily Traffic

8. Determine the acquired road-structure thickness.

| M998 HMMWV         |
|--------------------|
| M929 5-ton dump    |
| 600                |
| (2 average trucks) |

a. First, look at the required road thickness if it was not designed for frost. In this case, the compact subgrade CBR = 8 is used in Figure G-2, page G-3. This results in a required total thickness of 6.25 inches, rounding up to 7 inches as shown below.

Available material CBR:
Natural subgrade = 4 (Clay PI = 14)
Compacted subgrade = 8
Fine-graded, crushed rock = 80
Coarse-graded, crushed rock = 80
Clean sand subbase = 15

## Solution:

1. Number of daily passes = 2,400 (given).
2. Select road class D from Table 9-8, page
9-59, based on average daily traffic of 2,400. 3. Select traffic category IV from page 9-
59, based upon the presence of the 25-percent truck traffic.

4. Select design index of 4 from Table 9-9, page 9-59.

5.
Natural subgrade CBR = 4.
Compacted subgrade CBR = 8
b. Now, design the road for frost. In this case, the natural subgrade CBR = 4, and the frost-area soil-support index = 3.5.

Since the natural subgrade CBR is greater than the frost-area soil-support Index, Figure G-1 is used. A design index of 4 is entered into Figure G-1 resulting in a

## Notes:

design thickness of 24.5 inches, rounding up to 25 inches. Notice the rather large difference in design thicknesses between frost design and non frost design.

9. Compaction densities for each layer are determined from Table 9-12, page 9-60.

1. The function of the subbase as a filter
layer is not always required, depending
upon the subgrade material. In this case,
the subgrade is a CL; therefore, it is re-
quired.

   Wearing course:
                    at least 100 percent.
   Base course:
                 at least 100 percent.
   Subbase course:
                    100 to 105 percent.
   Subgrade: 90 to 95 percent for cohesion
soil (PI>5).

2. For economy, the thicknesses of the
base and subbase courses can be ad-
justed, so long as the minimum thickness
above the CBR=15 subbase is maintained
at 4 inches, as determined from Figure G-
2, page G-3.

10. Draw the section of the frost-area, ag-
gregate road structure.

3. An overall minimal thickness layer of
4 inches should be maintained.

When using a geotextile as a filter layer, the
design above could be used by deducting 6
inches of the clean sand subbase and
replacing it with a geotextile. The total
thickness above the geotextile must be a
minimum of 25 inches. Two alternate
designs using geotextile are shown in the
example at the bottom of the page.

## Appendix H Geotextile Design Design Guidelines

The widespread acceptance of geotextiles for use in engineering designs has led to a proliferation of geotextile manufacturers and a multitude of geofabrics, each with different engineering characteristics from which to choose. The design guidelines and methodology that follow help you select the right geofabric to meet your construction requirements.

## Unpaved-Aggregate Design Site Reconnaissance

As with any construction project, a site reconnaissance provides insight on construction requirements and potential problems.

## Determine Subgrade Soil Type And Strength

Identify the subgrade soil and determine its strength as outlined in Chapter 9, FM 5-
410. If possible, determine the soil's shear strength, C, in psi.

If you are unable to determine C, use the nomograph in Figure H-1 to convert CBR value or CI to C.

## Determine Permissible Load On The Subgrade Soil

The amount of loading that can be applied without causing the subgrade soil to fail is referred to as the permissible stress, S.

Z Permissible subgrade stress without a
geotextile:
- Permissible subgrade stress with a
geotextile:

## Determine Wheel Loads, Contact Pres- - Estimate The Area Being Loaded Sure, And Contact Area

Estimate wheel loads, contact pressure, and contact-area dimensions from Table H-2. For geotextile design, single and dual where
= length of one side of the square wheels are represented as single-wheel contact area loads (L) equal to one-half the axle load, The wheel load exerted by a single wheel is Determine Aggregate-Base Thickness applied at a surface contact pressure (P)
Assuming that wheel loads will be applied equal to the tire inflation pressure. Dualover a square area, we can use the Bouswheel loads apply a P equal to 75 percent sinesq theory of load distribution to deterof the tire inflation pressure. Tandem axles mine the aggregate-section thickness reexert 20 percent more than their actual quired to support the design load. Bousweight to the subgrade soil due to overlapsinesq theory coefficients are found in Table ping stress from the adjacent axle in the H-2.

tandem set,

## H-2 Geotextile Design Adjust Aggregate-Section Thickness For Aggregate Quality

The design method is based on the assumption that good-quality aggregate (minimum CBR value of 80) is used. If lower-quality aggregate is used, the aggregate-section thickness must be adjusted.

Table H-3, page H-4, contains typical compacted strength properties of common structural materials. These values are approximations: use more specific data if it is available. Extract the appropriate thickness equivalent factor from Table H-3, then divide H by that factor to determine the adjusted aggregate-section thickness.

Adjust Aggregate-Base Thickness for Service Life If the trafincrease H
The design method assumes that the pavement will be subjected to 1,000 passes of the maximum design axle load.

fic is greater than 1,000 passes, by the following percentages:

2,000 passes
8%
5,000 passes
19%
10,000 passes
27%

Z First, solve for X.
If you anticipate more than 10,000 passes, you need to increase the design thickness by 30 percent and monitor the performance of the road.

Without a geotextile: With a geotextile:

Z Using the calculated values of X and
             find the corresponding value
of M and                from Table H-2.
Z Then solve for aggregate-base thickness
H and H geotextile.
Without a geotextile:
With a geotextile:
The difference between H and H geotextile is the aggregate savings due to the geotextile.

A second method of determining minimum required cover above a subgrade for wheeled vehicles with and without a geotextile requires fewer input parameters. Again, use Figure H-1 to correct CBR or CI values to a C value. Determine the permissible stress on the subgrade soil (S) by multiplying C by
2.8 without a geotextile and by 5.0 with a geotextile. Select the heaviest vehicle using the road and the design vehicle for each wheel-load configuration: single, dual, or tandem. Enter the appropriate graph (see Figures H-2, H-3, or H-4, pages H-5
through H-7) at S (with and without a geotextile). Round design-vehicle wheel loads to the next higher 5,000-pound increment. Determine the intersection between the appropriate wheel-load curve and S
(with and without a geotextile), then read the minimum required thickness on the left axis. Use the greatest thickness values as and size are irregular in nonwoven fabrics.

the design thickness with and without a ments.

The pattern and opening spacing geotextile. Compare the cost of the material saved with the cost of the geotextile to determine if the use of the geotextile is cost effective.

Woven fabrics are generally stronger than nonwoven fabrics of the same fabric weight.

Woven geotextiles typically reach peak tensile strength at between 5 and 25 percent strain. Nonwoven fabrics have a high elongation of 50 percent or more at maximum strength.

Up to this point in the geotextile-design process, you have been concerned with general design properties for designing unpaved aggregate roads. Now you must decide which geotextile fabric best meets your project requirements.

## Types Of Geotextiles

Table H-4, page H-8, provides information on important criteria and principal properties useful when selecting or specifying a geotextile for a specific application. The type of equipment used to construct a road or airfield pavement structure on top of the geotextile must be considered. Equipment ground pressure (in psi) is an important factor in determining the geotextile fabric thickness; a thicker fabric is necessary to stand up to high equipment ground pressure (see Table H-5, page H-9).

There are two major types of geotextiles:
woven and nonwoven. Woven fabrics have filaments woven into a regular, usually rectangular, pattern with fairly even opening spacing and size.

Nonwoven fabrics have filaments connected in a method other than weaving, typically needle punching or head bonding at intersection points of the fila-

## H-4 Geotextile Design

Once the required degree of geotextile survivtesting standards, the geotextile will be reability is determined, minimum speification quired to withstand to meet use and conrequirements can be established based on struction requirements, you are ready to ASTM standards (see Table H-6, page H-
either specify a geotextile for ordering or
10). When you have determined the set of evaluate on-hand stocks.

## Roadway Construction

There is no singular way to construct maddeeper than 3 or 4 inches (see Figure H-5, ways with geofabrics. However, there are page H-11). Compact the subgrade if the several applications and general guidelines soil CBR is greater than 1. The compaction that can be used.

aids in locating unsuitable materials that may damage the fabric. Remove unsuitable SITE PREPARATION
materials where practical.

Clear, grub, and excavate the site to design grade: fill in ruts and surface irregularities When constructing over extremely soft soils
(such as peat bogs), surface materials (such as the root mat) may be advantageous and should be disturbed as little as possible.

grade. The fabric is commonly, but not always, laid in the direction of the roadway. Where the subgrade cross section has large areas and leveling is not practical, the Use sand or sawdust to cover roots, stumps, fabric may be cut and laid transverse to the or stalks. This cushions the fabric and roadway. Large wrinkles should be avoided.

reduces the potential for fabric puncture.

In the case of wide roads, multiple widths of Nonwoven geotextiles are preferred when the fabric are laid and overlapped. Lap length soil surface is uneven.

normally depends on subgrade strength.

Table H-7, page H-12, provides general guidelines for lap lengths.

## Laying Of Fabric

The fabric should be rolled out by hand, ahead of backfilling, directly on the soil sub-

## H-6 Geotextile Design

puncture it.

Small, tracked bulldozers
(with a maximum ground pressure of 2 psi)
are commonly used for spreading. The blade is also kept high to avoid driving rock down into the fabric. After spreading, compaction and grading can be carried out with standard compaction equipment. If the roadway has side drains, they are constructed after the pavement.

If angular rock is to form the base, it is common to first place a protective layer of 6
to 8 inches of finer material, Base material is then end-dumped directly onto the previously spread load, pushed out over the fabric, and spread from the center using a bulldozer. Vehicles must not be driven directly on the fabric because they might

## Glossary

advanced airborne control platform
AABNCP
AASHO
American Association of State Highway Officials
American Association of State Highway and Transportation Officials
AASHTO
acrylonitrile-butadiene-styrene
(plastic)
ABS
asphalt cement
AC
armored combat earthmover
ACE
adjusted
adj
air base damage repair
ADR
Army Facilities Component System
AFCS
AFM
Air Force manual
Air Force pamphlet
AFP
Air Force regulation
AFR
aggregate
a g g
AHD
average haul distance
AML
airfield marking and lighting
ammo
ammunition
APC
armored personnel carrier
approx
approximately
April
Apr AR
Army regulation
American Society of Civil Engineers
ASCE
ASTM
American Society of Testing and Materials

Atterberg Limits Soil plasticity test used to measure soil cohesiveness: that is, cohesive or cohesionless,

| ATTN   | attention   |
|--------|-------------|
| Aug    | August      |

av
absolute volume
average daily traffic (ADT) The anticipated average number of vehicles per day that will
use a completed facility.
banked cubic yardage (BCY) Soil measured in its natural state.

average running speed
The speed expected to be maintained by most vehicles. It is equal
to the total traveled distance divided by total time consumed.
base course or base
Base course consists of well-graded, granular materials that have a
liquid limit less than 25 percent and a plastic limit less than 5 percent,
The base course is the most important element in a road structure. It
functions as the primary load-bearing component of the road, ultimately
providing the pavement (or surface) strength. Therefore, it is made of higher
quality material than subbase material.
bearing capacity
The ability of a soil to support a vehicle without undue sinkage of the
vehicle.
benching
Terracing on a slope.
berm
A raised lip, usually of earth, placed at the top edge of a channel to prevent
flow into the channel at places not protected against erosion.
bitumen or bituminous
The most common type of asphalt surface placed in the theater of
operations.

| Bn         | battalion                                                                |
|------------|--------------------------------------------------------------------------|
| borrow pit | An excavated area where material has been dug for use as fill at another |
| location.  |                                                                          |
| BTU        | British thermal unit                                                     |
| BVM        | Bays Village of Maryland                                                 |
| C          | Celsius                                                                  |
| C          | cut                                                                      |
| CAD        | computer-aided design                                                    |
| CAMMS      | Condensed Army Mobility Modeling System                                  |

California Bearing Ratio (CBR) A measure of the shearing resistance of a soil under
carefully controlled conditions of density and moisture.

| CDR                                                                       |
|---------------------------------------------------------------------------|
| CE                                                                        |
| 55                                                                        |
| Laboratory compactive effort (CE) accomplished by the impact of 55 hammer |
| blows per layer.                                                          |
CES
civil engineering squadron
CEV
combat engineer vehicle
cf
cubic feet
cfs
cubic feet per second
CH
clays, high compressibility (LL>50)
CI
cone index centerline
CL
clays, low compressibility (LL<50)
cm
centimeter
cm/sec
centimeters per second
CMD
command
CMP
corrugated metal pipe
co
company

coarse-grained soil A free-draining soil of which more than 50 percent by weight of the grains will be retained on a No. 200 sieve.

For traffic ability purposes, these are dry beach and desert soils usually containing less than 7 percent of material passing the No. 200 sieve.

Gravels are not considered to pose a trafficability problem.

compacted cubic yards (CCY) A measurement of compacted soil.

compaction
Process of mechanically densifying a soil, normally by the application of a
moving (or dynamic) load.
compactive effort (CE) Method used to compact the soil.

cone index (CI) An index of the shearing resistance of soil. The CI is obtained with a
cone penetrometer. The number represents resistance to penetration into the
soil of the 30-degree cone with a 1/2-square-inch base area (actual load in
pounds on cone base area in square inches), using a dial calibrated to produce an index of 300 when 150 lb of pressure are exerted on the handle.
The CI reading is normally taken at the 0-inch (base of the cone) and at
every 3-inch interval down to 18 inches or until the dial reaches the maximum of 300. A number of tests will be taken and each specified interval reading will be averaged.
That average becomes the CI for the inch
level.

CONUS
continental United States
CPT
captain

critical layer
The soil layer that determines the rating cone index (for fine-grained soil) or
cone index (for coarse-grained soil) of the area considered. Its depth varies with the soil profile and the weight and type of vehicle. Generally, the
critical layer for fine-grained soils is 6 to 12 inches below the surface when
subjected to passes of a vehicle.
For coarse-grained soils, the critical layer is
usually from the surface to a 6-inch depth for all vehicular passes.
crown
The difference in elevation between the centerline and the surface edge. The
crown expedites surface-water runoff on the road. The amount of crown depends on the surface used.
Surfaces such as concrete or bituminous
materials require little crown because of their impermeability, but permeable surfaces such as earth or gravel require a large crown.

The outside top of the culvert.
crown
CSS
cationic slow setting
cu cm
cubic centimeter
cu ft
cubic foot
CUCV
commercial utility cargo vehicle
culvert
An enclosed waterway used to pass water through a structure consisting of
an embankment or fill.

cut or cutting
That portion of through construction produced by the removal of the natural
formation of earth or rock, whether sloped or level. The terms sidehill cut
and *through-hill* cut describe the resulting cross sections commonly encountered.

cut slope

The slope from the top of a cut to the ditch line (bottom of ditch). Sometimes
it is called the back slope.

cy
cubic yard
Department of the Army
DA
DBH
diameter at breast height
Department of Defense
DD Dec
December degree
deg
department
dept

design hourly volume (DHV) The number of vehicles that a road may typically be expected
to accommodate in an hour. The DHV is 15 percent of the ADT.
design speed
The speed for which a facility is designed. Pertinent geometric features, such
as horizontal curves and grades, may be based on design speed.
design storm
The storm of greatest intensity for a given period. For example, a "2-year
design storm" is a storm expected to be equalled once in 2 years.

The storage of water in depressions in the earths surface.
detention
diameter
dia
dip
A paved ford used for crossing dry, wide, shallow arroyos or washes in semiarid regions subject to flash floods.
ditch slope

The slope of the ditch extending from the outside edge of the shoulder to the
bottom of the ditch. This slope should be relatively flat to avoid damage to vehicles driven into the ditch and to permit easy recovery.

A ditch used to transport water away from roadways or airfields.
diversion ditch
demilitarized zone
DMZ
drop
A structure that absorbs the impact energy of water as it falls vertically to a
lower level waterway. ditch time
DT
east
E elev
elevation
EM
engineer manual
EM
enlisted member
Engr
engineer
explosive ordnance disposal
EOD
erosion
The transportation of weathered materials by wind or water.
east-west
EW
F
fill
F
Fahrenheit
Feb
February
fill or filling
Material used to fill a receptacle, cavity, passage, or low place, Using
material to fill a cavity or low place.
fill slope
The incline extending from the outside edge of the shoulder to the toe (bottom)
of a fill.

fine-grained soil A silt or clay soil of which more than 50 percent by weight of the grains
will pass a No. 200 sieve (smaller than 0.074 millimeter in diameter).

FM
field manual
ford
A shallow place in a waterway where the bottom permits the passage of
personnel and vehicles.
fpm
feet per minute
fps
feet per second
natural
frost action
Processes which affect the ability of soil to support a structure when accumulated water in the form of ice lenses in the soil is subjected to
freezing conditions.
frost-susceptible soil
Soil in which significant ice segregation will occur when the
necessary moisture and freezing conditions are present.
ft
feet
FT
Fort
ft/ft
feet per foot
ft/in
feet per inch
square feet per square yard
G
gravel
gabion
Large, steel wire-mesh baskets filled with stones, usually rectangular in shape and variable in size.
They are designed to solve the problem of erosion.
gal
gallon
gal/lb
gallons per pound
gallons per square yard
GC
clayey gravel
geometric design (geometry or geometric features)
Refers to all visible features of the
road such as lane width, shoulder width, and alignment.
grade-line elevation
GLE
silty gravel
GM
gram
gm
poorly graded gravel
GP
To level off to a smooth horizontal or sloping surface.
grade
An icing whose source of water is from groundwater flow above permafrost.
ground icing

groundwater table The upper limit of the saturated zone of free water.

| gunite                                      | A mixture of cement, sand, and water sprayed from a high pressure nozzle   |
|---------------------------------------------|----------------------------------------------------------------------------|
| onto a surface to protect it.               |                                                                            |
| GW                                          | well-graded gravel                                                         |
| HMMWV                                       |                                                                            |
| high mobility, multipurpose wheeled vehicle |                                                                            |
| HP                                          | high point                                                                 |
| HW                                          |                                                                            |
| high water                                  |                                                                            |

hydraulic gradient
The slope in feet per foot of a drainage structure.

hydrologic cycle The continuous process in which water is transported from the oceans to

the atmosphere to the land and back to the sea.

An irregular sheet or field of ice.
icing
inch
in
The absorption of rainwater by the ground on which it falls.
infiltration
inches per hour
in/hr
Soil in its natural (undisturbed] state.
in situ
The holding of rainfall in the leaf canopy of trees and plants.
interception
January
Jan
July
Jul
June
Jun
kilogram
kg
kilopound (1,000 pounds)
kip
km
kilometer
kilometers per hour
kph
laminar flow
The type of flow that occurs when viscosity forces predominate and the
particles of the fluid move in smooth, parallel paths.
latitude
lat
pound
lb
LIP
length in place
liq
liquid
LL
liquid limit
LOC
lines of communication
LP
low point
M
silt
m
meter
Mar
March
mass diagram
Earthwork volume plotted on graph paper, showing cut and fill operations.
max
maximum
maximum towing force (T1) The maximum continuous towing force in pounds a vehicle
can exert.
It is expressed as a ratio or percentage of vehicle weight.
MD
Maryland
MH
silt, high compressibility (LL>50)
mi
mile
min
minimum
min
minute
ML
silt, low compressibility (LL<50)
mm
millimeter
MO
maximum offset
MO
Missouri
mobility index (MI) A number that results from a consideration of certain vehicle
characteristics. mission-oriented protective posture
MOPP
miles per hour
mph
medium setting
MS
Slipperiness symbol meaning not slippery under any conditions.
N
north
N
not applicable
N/A
North Atlantic Treaty Organization
NATO
nuclear, biological, chemical
NBC
noncommissioned officer
NCO
northeast
NE
nonfrost susceptible
NFS
number
No.
November
Nov
number of pipes
NP
NRMM
NATO Reference Mobility Model
naval radio station
NRS
north-south
NS
national stock number
NSN

offset
October
Ott
order length
OL
Slipperiness symbol meaning slippery when wet.
P
point of curvature
PC
permanent
perm
Constantly frozen ground.
permafrost
possibly frost susceptible
PFS PI
plasticity index point of intersection
PI
petroleum, oils, and lubricants
POL
The accumulation of water at the upstream end of a culvert.
pending
population
pop
probability
R
prime base engineer emergency forces
Prime BEEF

psi
pounds per square inch
PT
point of tangency
PVC
polyvinyl chloride
PVC
point of vertical curvature
PVI
point of vertical intersection
PVT
point of vertical tangency

QSTAG
Quadripartite Standardization Agreement

rating cone index (RCI) The measured cone index multiplied by the remolding index (RCI =
CI x RI). The RCI expresses the soil-strength rating of a soil area subjected to sustained traffic.

RC
rapid curing

RED HORSE
rapid engineering deployable heavy operational repair squadrons, engineering
remoldable sand A poorly drained, coarse-grained soil, usually containing 7 percent or
more material passing a No. 200 sieve.
Poor internal drainage increases the
water content greatly influencing the trafficability characteristics and
permitting the remolding test to be performed. When wet, these soils react
to traffic in a manner similar to fine-grained soils and are more sensitive to remolding.
remolding
The changing or working of a soil by traffic or a remolding test. The beneficial, neutral, or detrimental effects of remolding may change soil strength.
remolding index (RI) The ratio of remolded soil strength to original strength. Soil conditions that permit the remolding test to be performed with ease will usually result in a loss of strength.

Reqd
required

required towing force (T2) The force in pounds required to tow an operable, powered
vehicle on level terrain.

RI
remolding index

riprap
Rocks or rubble placed in the bottom and on the sides of a ditch to prevent
soil erosions.
river icing
An icing formed along rivers or streams and adjacent areas having a source
of water above or below the riverbed.
roadbed
The entire width of surface on which a vehicle may stand or move. The
roadbed consists of both the traveled way and the shoulders.
road classification system An organized list of four road types based on the number of
vehicles each is designed to accommodate in a 24-hour period, Road
characteristics are based on average daily traffic.
roadway
The entire width within the limits of earthwork construction and is measured
between the outside edges of cut or fill slopes. Roadway width does not
include interceptor ditches if they fall outside the slopes, The roadway width
varies from section to section depending on the height of cut or fill, depth of
ditches, and slope ratios.

RR
railroad
rapid runway repair
RRR
rapid setting
RS
road tar
RT
road tar cutback
RTCB
radiotelephone operator
RTO
Slipperiness symbol meaning slippery at all times,
S
sand
S
Intelligence Officer (US Army)
S2
S3
Operations and Training Officer (US Army)

sand grid
A honeycomb shaped geotextile measuring 20 feet by 8 feet by 8 inches deep
when fully expanded.
It is used to develop a beachhead for logistics-over-theshore operations.
It is also useful in expedient revetment construction.

SC
supply catalog
SC
slow curing
SCIP
scarify and compact in place
SEATO
Southeast Asia Treaty Organization
sec
second
Sept
September
SFC
sergeant first class

shoulder
That part of the top surface of an approach embankment, causeway, or cut
immediately adjoining the roadway that accommodates stopped vehicles in
emergencies and laterally supports base and surface courses.
shoulder slopes These may be the same as the traveled way, but usually they are greater
because shoulders are more previous than the surface course.
sight distance restriction factor The percent of the total length of the road on which the
sight distance is less than 1,500 feet.
slipperiness
The low traction capacity of a thin soil surface owing to its lubrication by water or mud without the occurrence of significant vehicle sinkage.

The inclined surface of an excavated cut or an embankment.
slope slope ratio

The relative steepness of the slope expressed as a ratio of horizontal distance
to vertical distance. Thus, a 2:1 slope ratio signifies that for every 2 feet horizontally there is a rise or fall of 1 foot.
The value of the slope ratio used
in construction depends on the properties of the soil and the vertical height of the slope. Ditch slopes may also be governed by the amount of water to be drained and the possibility of erosion.

silty sands and poorly graded sand-silt mixture
SM
standing operating procedure
SOP
poorly graded sand
SP
An icing whose source of water is from subpermanent levels.
spring icing
square
sq
square feet
sq ft
sq in
square inch
senior
Sr
slow setting
SS
staff sergeant
SSG
station
sta
Standardization
Agreement
STANAG
stickiness
The ability of a soil to adhere to the vehicle undercarriage or running gear.
A structure used to protect the culvert outlet against erosion.
stilling basin

subbase or subgrade Describes the in situ soil on which a road, airfield, or heliport is
built. The subgrade includes soil to the depth that may affect the structural
design of the project or the depth at which climate affects the soil.
subsurface water Water beneath the surface of the land.

superelevation The transverse downward slope from the outside to the inside of the
traveled way on a curve.
It is usually expressed in inches of drop per
horizontal foot or foot-drop per horizontal foot.
surface course The surface course provides a smooth, hard surface on which the traffic
moves.
It may be constructed from asphalt or tar products, concrete, gravel,
or compacted earth with certain types of binders. The surface course should be all-weather and should provide for the rapid runoff of water. The use of
treated surfaces is limited to roads that have a long design life. A divisional road with a life expectancy of 6 months or less will receive only an earth or
gravel surface.

| SUSV                  | small-unit support vehicle   |
|-----------------------|------------------------------|
| SW                    |                              |
| southwest             |                              |
| SW                    |                              |
| well-graded sand      |                              |
| T1                    | maximum towing force         |
| T2                    |                              |
| required towing force |                              |
| TBM                   |                              |
| temporary bench mark  |                              |
| TC                    | training circular            |

temp
temperature
time of concentration (TOC) The time it takes for an entire drainage basin to begin
contributing runoff to a drainage structure.
TM
technical manual

TN
air transport
TO
theater of operations
TOE
table(s) of organization and equipment

TP
transition point
traction capacity The ability of soil to resist the vehicle tread thrust required for steering
and propulsion.
traffic lane
The traffic lane consists of the road surface over which a single lane of traffic
will pass,
transpiration
The process by which water that has traveled from the ground through the
plant's system is returned to the air through the leaf system.
traveled way
The road surface upon which all vehicles move or travel. For a single-lane
road, the traveled way is the same as one traffic lane. For a multilane road,
the traveled way is the sum of the traffic lanes, If a surface course is
provided, it normally extends only across the traveled way.
turbulent flow The type of flow that occurs when viscosity forces are relatively weak and
the individual water particles move in random patterns within the aggregate
forward-flow pattern.

US
United States
USAES
US Army Engineer School
U s e s
Unified Soil Classification System
UXO
unexploded ordnance
VC
vitrified clay

vehicle cone index (VCI) The index assigned to a given vehicle that indicates the minimum
soil strength in terms of rating cone index (or cone index for coarse-grained soil) required for one pass        or other passes (VCI) of the vehicle.
Usually one and fifty passes are used as extremes.

visual meteorological conditions
VMC
volume
Vol
weight of a towing vehicle
W1
weight of a towed vehicle
W2
with
w/
without
w/o
WF
waste factor wetted perimeter
wp
wire rope cable
W.R.C.
weight
wt
weight type
WT
yd
yard
year
yr
<
less than
less than or equal to
>
greater than greater than or equal to
change of grade

## References Sources Used These Are The Sources Quoted Or Paraphrased In This Publication. Standardization Agreements (Stanags And Qstags)

QSTAG 306, *Fortification for Parked Aircraft* 14 June 1978.
STANAG 2929.
Airfield Damage Repair. 11 January 1989.
STANAG 3346 AML (Edition 4). Marking and Lighting of Airfield Obstructions.
17 October 1988.
STANAG 3601 TN (Edition 3). Criteria for Selection and Marking of Landing Zones for Fixed
Wing Transport Aircraft. 2 July 1985.
STANAG 3619 AML (Edition 2, Amendment 2). *Helipad Marking.* 7 October 1980.
STANAG 3652 AML (Amendment 3). Helipad *fighting, Visual* Meteorological Conditions.
1 March 1979.
STANAG 3685 AML. *Airfield Portable Marking.* 26 April 1988.

## Joint And Multiservice Publications

AR 415-30/AFR 93-10.
Troop Construction and Engineering Support of the Air Force
Overseas.
15 May 1979.
FM 5-430-00-2/AFPAM 32-8013, Vol 2. Planning and Design of Roads, Airfields, and Heliports in the Theater of Operations:
Volume 2, Airfield and Heliport Design. To be published
within six months.
FM 5-530. *Materials Testing.* (NAVFAC MO-330; AFM 89-3.) 17 August 1987.
TM 5-624. Maintenance and Repair of Surface Areas.
(NAVFAC MO-102: AFR 85-8.)
31 March 1977.
TM 5-822-2. General Provisions and Geometic Design for Roads, Streets, Walks, and
Open Storage Areas.
(NAVFAC DM-5.5; AFM 88-7, Chap 5,) 14 July 1987.
TM 5-822-5, *Pavement Design for Roads, Streets, Walks, and Open* Storage Areas.
(AFM 88-7, Chap 1.) 12 June 1992,
TM 5-825-2. *Flexible Pavement Designs for Airfields.* (NAVFAC DM-21.3; AFM 88-6.)
1 August 1978.
TM 5-852-7. Surface Drainage Design for Airfields and Heliports in Arctic and Subarctic
Regions (AFM 88-19, Chap 7.) 15 April 1981,

## Air Force Publications

AFR 93-2. *Contingency Response Planning. 19* January 1990.

## Army Publications

FM 5-34. *Engineer Field Data.* 14 September 1987,
FM 5-36. *Route Reconnaissance and Classification.* 10 May 1985.
FM 5-233. *Construction Surverying.* 4 January 1985.
FM 5-250. *Explosives and Demolitions.* 15 June 1992.
FM 5-410. *Military Soils Engineering.* 23 December 1992.
FM 5-434. *Earthmoving Operations.* 30 September 1992.
FM 5-446. *Military Nonstandard Fixed Bridging.* 3 June 1991.
MIL-STD-621. Test Methods for Pavement Subgrade, Subbase, and Base Course Material.
22 December 1964.
SC-6635 -98-CL-E02-HR. Hand Receipt Catalog Covering Content of Test Set, Soil.
19 April 1982.
Special Report 83-27. Revised Procedures for Pavement Design Under Seasonal Frost
Conditions, US Army Corps of Engineers.
Office of the Chief of Engineers, Washington,
DC 20314. September 1983.
TM 5-232. *Elements of Surveying.* 1 June 1971.
TM 5-302-Series. *Army Facilities Components System: Design. 28* September 1973.
TM 5-332. *Pits and Quarries.* 15 December 1967.
TM 5-337. *Paving and Surfacing Operations.* 21 February 1966.
TC 5-340. *Air Base Damage Repair (Pavement Repair]. 27* December 1988.

## Nonmilitary Publications

ASTM D1557. Soil and Soil Aggregate Mixture Using 10 Pounds 4.54KJ Rammer and 18-Inch
457 mm Drop, Moisture Density Relation of 27 Apr 78. 1989.
ASTM D1633. *Compression Strength of Molded Soils Cementing Cylinders.* 1990.
ASTM D3786. Test Method for Hydraulic Bursting Strength of Knitted Goods and Nonwoven
Fabrics: Diaphragm Bursting Strength Tester Method. 1987.
ASTM D4533. *Test Method for Trapezoid Tearing Strength of Geotextiles.* 1991.
ASTM D4632. Test Method for Breaking Load and Elongation of Geotextiles (Grab Method).
1991.
ASTM D4833. Test Method for Index Puncture Resistance of Geotextiles Geomembranes,
and Related Products. 1988.

## Documents Needed These Documents Must Be Available To The Intended Users Of This Publication.

DA Form 1248. *Road Reconnaissance Report.* July 1960.
DA Form 1711-R. *Engineer Reconnaissance Report (LRA).* May 1985.
DA Form 2028. *Recommended Changes to Publications and Blank* Forms. February 1974.
DD Form 2641. *Trafficability Test Data.* August 1993

## Index A

AASHTO. *See* American Association of State Highway and Transportation Officials
(AASHTO) method T96.

abnormal strength profile, 7-8 ADR. *See* airfield and heliport maintenance, air base damage repair (ADR).

ADT. *See* average daily traffic (ADT).

aerial photo, 7-28

aggregate, 9-55
bituminous construction, 9-47
desirable characteristics, 9-47
identification, 9-47
rolling, 9-56
spreading, 9-56
traffic control, 9-57. *See also* road maintenance, with traffic and baton method.
AHD. *See* average haul distance (AHD).

airfield and heliport maintenance, 8-17
air base damage repair (ADR). 8-17
Air Force responsibilities, 8-17 Army responsibilities, 8-17
ice control, 8-20. *See also* ice control.
maintenance during flying operations, 8-21
mud control, 8-18 rehabilitation of captured airfields, 8-21
snow removal, 8-20
turf surfaces, 8-18
alignment, 2-3, 9-6 alluvial terraces, 2-2
American Association of State Highway and Transportation Officials (AASHTO) method T96,
9-48
Army track. *See* roads, Army track.

asphalt distributor, 9-57
asphalt pavement, minimum thickness, 9-71 asphalts and tars, 9-45 average daily traffic (ADT), 9-4 average haul distance (AHD), 3-23

## B

balance lines, 3-22
baton method, 8-11. *See also* road maintenance, with traffic

base course, 5-10
compaction, 5-11 gradation, 5-11
liquid limit, 5-11
materials, 5-11, 5-12 natural materials, 5-13
other materials, 5-14 plasticity index, 5-11
processed materials, 5-13
requirements, 5-11
base flow, 6-9 berm, 6-51
bituminous base, 5-15
materials, 9-41 pavements, 9-69
cold-laid, bituminous-concrete plant mix, 9-69
design, 9-71 design steps, 9-73
hot-mix, bituminous-concrete, 9-69
penetration macadam, 9-69
road mix, 9-69
sand asphalt mix, 9-69 sand-tar mix, 9-69
sheet asphalt mix, 9-69
stone-filled sheet asphalt mix, 9-69
types and uses, 9-69
bituminous surfaces. *See* maintenance, bituminous surfaces.

blind drain. *See* subsurface drainage, techniques, blind drains.

box-culvert flow, 6-77 bridge approaches, 2-3
bridges, 6-113.

See also road maintenance, fords and bridges.

Bureau of Reclamation, 6-125 burning pits, *See* forest clearing considerations, waste areas, burning pits,

## C

C variable, *See* rational method of estimating runoff, formula variables, C variable.

CAD, *See* end-area-determination method, computer -aided design (CAD).

calcium chloride, 8-7, See *also* ice control, calcium chloride and maintenance, gravel surfaces, use of calcium chloride, CAMMS. *See* Condensed Army Mobility Modeling System, camouflage. *See* forest clearing considerations, camouflage and tactical considerations, camouflage.

causeways, 6-112
CBR, 5-1. *See also* design CBR, values and roads, CBR requirements.

cement grades, 9-45 channel flow. *See* ditches, types of flow, channel.

channels construction and maintenance, 6-53 special, 6-51
gutters, 6-51
median, 6-51
characteristics of grasses, 8-19
check dams, 8-3
chespaling. *See* roads, chespaling. chord-length calculations, 9-14
CI. *See* cone index (CI). clearing equipment.

See clearing, stripping, and grubbing; clearing with equipment, clearing, stripping, and grubbing, 4-1
clearing with equipment, 4-6
extreme slopes, 4-12 grader, 4-15
large trees, 4-9 medium trees, 4-8
ripper, 4-15
Rome plow, 4-10
small trees, 4-8 tractor-mounted winches, 4-13 tree dozer, 4-10
truck-mounted winches, 4-14 winches, 4-13
windrowing. 4-11
clearing with explosives, 4-15
boulders, 4-15 trees and stumps, 4-15
felling equipment, 4-14 limitations of engineer equipment, 4-7, 4-8
performance techniques, 4-6
proper application of engineer equipment, 4-6 removing buried explosives, 4-17
unexploded ordnance (UXO), 4-17
removing structures, 4-17
removing surface rocks, 4-15
stripping, 4-17
unsuitable soil, 4-17
climate classifications of forests, 4-1
dry forests, 4-2
monsoon forests, 4-2
rain forests, 4-2
temperate forests, 4-1
CMP, *See* culverts, corrugated metal pipe (CMP).

coarse-grained soils, 7-37, See also strength profile, coarse-grained soils.

operations, 7-26
cold climates, hydraulic criteria, 6-102
compaction, 5-4
clays that lose strength, 5-6 select materials, 5-9
silts, 5-6
subbase materials, 5-9 swelling soils, 5-7
Condensed Army Mobility Modeling System (CAMMS), 7-1
cone index (CI), 7-2
range, 7-5
requirements, equipment, D-1
cone penetrometer, 7-4 construction airfield, 1-2
Air Force responsibilities 1-2 Army responsibilities, 1-2
drainage, 6-1
methods, 9-49
operations, 5-15
blending and mixing, 5-16
compacting, 5-16
fine grading, 5-15 finishing, 5-17 hauling: placing, and spreading, 5-16
watering base materials, 5-16
road, 1-2
construction stakes, 3-3
alignment, 3-3 centerline, 3-3 culvert, 3-6
finish-grade, 3-5
hub, 3-3
offset, 3-5 reference, 3-6
slope, 3-4
construction surveys, 3-1
bench marks, 3-6 earthwork estimation, 3-6
final location, 3-2
horizontal control, 3-2
vertical control, 3-2
layout, 3-2
preliminary, 3-2
reconnaissance, 3-2
coral, *See* maintenance, coral surfaces.

corduroy. *See* roads, corduroy-surfaced. corrugations, 8-6 cutbacks, 9-45 covered-aggregate surface treatment.

See surface treatments, covered aggregate, critical layer, 7-3
depth variations, 7-3
critical slope, 6-77
crowned section, 9-25
culverts, 6-59
alignment, 6-60
assembling nestable CMP, 6-59 backfill, 6-70 bedding (foundations), 6-68 concrete box, 6-60
concrete pipe, 6-59
corrugated metal pipe (CMP), 6-59
cover, 6-63 depth of fill, 6-63
design, 6-73
with submerged inlets, 6-77 with unsubmerged inlets, 6-78
erosion control, 6-72
headwalls, wing walls, and aprons, 6-71 hydraulics, 6-73 maximum permissible cover for CMP, 6-68 maximum permissible cover for corrugated alumin urn-alloy pipe, 6-69 slope, 6-62 types and designs, 6-59
construction, 6-60
design, 6-73 expedient, 6-60
permanent, 6-59
curves
1-degree method, 9-8, F-1
compound, 9-7
horizontal, 9-7
design, 9-10 point of curvature (PC), 9-7 point of intersection (PI), 9-7 point of tangent (PT), 9-7
reverse, 9-6
simple, 9-6
spiral, 9-7
vertical, 9-19
allowable rate of change of grade (r), 9-20
change of grade (AG), 9-20
design, 9-20
elements, 9-19
frequency of placing survey stakes, 9-20
length determination, 9-20
length factor (k), 9-20
sight distance (S), 9-20
types, 9-19 using metric units, 9-25
curve tables, F-1 cut operation, 3-20

## D

DBH. *See* tree diameters at breast height (DBH)
design index, 9-59
pneumatic-tired vehicles, 9-59
life, 9-60
special considerations, 9-75
frost, 9-75
stabilized soil, 9-75
design CBR
base course, aggregate surfaces, 9-63
base course, flexible pavement, 9-70 values selection, 5-10 subsoil, 5-7
subgrade, 5-7
design considerations, 5-1
pavement structures, 5-1
design hourly volume (DHV), 9-4 detention.

See drainage, hydrology, detention.

DHV. *See* design hourly volume (DHV).

dips, 6-111
dissipators, 6-125 ditches design considerations, 6-45
location, 6-45
proposed lining, 6-45
quantity of runoff (Q), 6-45 slope (S), 6-45
design techniques, 6-46
steps, 6-46
diversion, 6-38
interceptor, 6-38
longitudinal slope or grade (S), 6-43
nonsymmetrical, 6-39
side, 6-38
side-slope back, 6-39
ditch, 6-39
front, 6-39 nonsymmetrical, 6-39
ratio, 6-39 symmetrical, 6-39
trapezoidal, 6-39 triangular, 6-39
types of flow, 6-40
continuous, 6-40 laminar, 6-40
open channel, 6-40 steady, 6-40
turbulent, 6-40
uniform, 6-40
V-type, 6-39
velocity of flow (V), 6-42
ditching, 6-3
interception, 6-3
drags, 8-4 drainage. *See* also construction, drainage.

base, 6-92
design in arctic and subarctic regions, 6-102
hydrology, 6-4
detention, 6-4
infiltration, 6-4
intercepting, 6-92
interception, 6-4 precipitation, 6-4
runoff, 6-4, 6-8
storms, 6-4
subgrade, 6-92 transpiration, 6-4
weather data, 6-6

drainage-system design, 6-11
available resources, 6-11
design data requirements, 6-11 meteorological data, 6-11 procedures, 6-11
delineating watersheds, 6-13 designing for maximum runoff, 6-19
determining area contributing runoff, 6-12
determining size, 6-17
establishing drainage-structure locations, 6-12
estimating quantity of runoff, 6-19
soil characteristics, 6-11
topographical information, 6-11
drop inlets and gratings, 6-89
construction, 6-89
maintenance, 6-91
dry season, 7-27 dust control, 8-5
dustproofing, 9-51

## E

earthwork, 2-3
operations, 2-3
earthwork volume sheet, 3-18 edge raveling, 8-8
emulsions, 9-47

end-area-determination methods, 3-7
computer -aided design (CAD), 3-13 double-meridian triangle, 3-10
planimeter, 3-12 stripper, 3-9 trapezoidal, 3-7
engineering fabrics, 9-77.

engineering study, 1-3
entrances.

See entrances, exits, and segments.

entrances, exits, and segments, 9-60.

environmental conditions, 4-1
EOD, *See* explosive ordnance disposal (EOD).

equivalency factors, application, 9-75 erosion control, 6-54, 6-114. *See also* culverts, erosion control, culvert outlets, 6-124 culvert transitions, 6-124 plain outlets, 6-124 stilling basins, 6-125
estimating runoff. *See* rational method of estimating runoff.

exits. *See* entrances, exits, and segments. explosive ordnance disposal (EOD), 4-17 external distance, 9-9

## F

fabrics, 9-77 field identification, 9-41 fill operation, 3-20
fine-grained soils, 7-36.

See also strength profile, fine-grained soils.

flexible-pavement structure, 9-69
bituminous-pavement mix, 9-71 bituminous-pavement thickness requirement, 9-71
compaction requirements, 9-71
materials, 9-70 minimum base-course thickness, 9-71
select materials and subbase, 9-70 supply sources, 9-70
typical flexible-pavement section, 5-1
flight-way obstructions, 2-4
glide angle, 2-4
flow. *See* ditches, types of flow. fords, 6-107, *See also* road maintenance, fords and bridges.

approaches, 6-110 bottom material, 6-108 channel condition, 6-110
construction, 6-110
cross section, 6-110 flood flow 6-110
high-water determination, 6-109 maintenance, 6-111
marking. 6-111
reconnaissance, 6-108 requirements, 6-108
stream velocity, 6-110
forest clearing considerations, 4-4
airfield approach zones, 4-6 camouflage, 4-4
disposal, 4-5
permafrost, 4-4
safety, 4-4 temporary drainage, 4-4 timber salvage, 4-4
waste areas, 4-5
burning, 4-5
burning pits, 4-5
clearing and piling stumps, 4-6
dumps, 4-5
fire control, 4-5
log piles, 4-6
off-site areas, 4-5
revetments, 4-5
forest types, 4-1.

See also climate classifications of forests.

French drain. *See* subsurface drainage, techniques, French drains.

frost boils, 8-16
heaves, 8-16
special considerations, 5-15
frost action potential, 5-10
frost design for roads, G-1
frost susceptibility of subgrade, 5-8 future expansion, 2-5

## G

gabions, 6-119
installation, 6-120
uses, 6-122
geofabrics, 9-77 geologic and permafrost conditions, 4-2
hardpan or rock, 4-2 inundated, marshy, and boggy areas, 4-2
permafrost, 4-2
geology, 2-2
rock outcropping, 2-2
sedimentary rocks, 2-2
geometric design process, 9-1
geometric formulas, B-1
geotextiles, 9-77 glide angle. See flight-way obstructions, glide angle, grade determination, 9-19
grade line, 5-4 grader. *See* clearing, stripping, and grubbing; clearing with equipment, gradation requirements, 9-29
grasses. *See* characteristics of gasses.

grating, 6-89 ground cover, 2-4 gunite lining, 6-115

## H

horizontal-curve elements. See curves, horizontal. hydrophobic, 9-48
hydraulic criteria for cold climates.

See cold climates, hydraulic criteria.

hydraulic gradient, 6-74 hydraulic radius (R), 6-45
calculating, 6-46
hydraulics of culverts. See culverts, hydraulics. hydraulic tables and curves, C-l hydrography construction, 6-10 hydrologic tables and curves, C-1 hydrology. *See* drainage, hydrology.

## I

I variable. *See* rational method of estimating runoff, formula variables, I variable.

ice control.

See also airfield and heliport maintenance, ice control and road maintenance, winter, surface ice control, abrasives, 8-15
calcium chloride, 8-15
mechanical removal, 8-15 salts, 8-15
ice road. See roads, snow and ice.

icing, 6-105
ground, 6-106, 6-107 measures against, 6-107
river, 6-106, 6-107
spring, 6-107
types, 6-105
infiltration.

See drainage, hydrology, infiltration.

intensity-duration curves. *See* standard rainfall intensity-duration curves.

interception. *See* drainage, hydrology, interception and drainage, interception.

## L

lag time, 6-9
laminar flow. *See* ditches, types of flow, laminar.

land clearing, 4-1
landing mats.

See roads, landing mats.

layout techniques, 9-15
length of curve (L), 9-9
level terrain all-wheeI drive vehicles, 7-12, 7-25
self-propelled vehicles, 7-12 tracked vehicles, 7-12, 7-24
vehicles towing inoperable, powered vehicles, 7-17, 7-18 vehicles towing other vehicles, 7-14
load distribution, 5-2
LOC. *See* preconstruction phase, location factors, lines of communication (LOC).

## M

macadam, 5-14
applying screenings, 5-17
compacting, 5-17 preparing subgrade, 5-17 special procedures for base, 5-17
spreading, 5-17
maintenance bituminous surfaces, 8-7
inspection, 8-7 patches, 8-7 maintenance of shoulders, 8-7
temporary repairs, 8-7
coral surfaces, 8-8 crater repair, 8-8
drainage, 8-2
culverts, 8-3 ditches, 8-3 shoulders, 8-3
surface, 8-3
gravel surfaces, 8-5
repair of potholes, 8-6
treatment of corrugations, 8-6 use of calcium chloride, 8-7
inspections, 8-2
drainage, 8-2
surface, 8-2
materials, 8-2 nonpaved surfaces, 8-3
oiled surfaces, 8-5
processed material surfaces, 8-7
rigid pavements, 8-8

stabilized soil surfaces, 8-8
potholes, 8-8
ravels, 8-8
maintenance and repair of surfaces, 8-1, 9-58
activities, 8-1
bituminous inspection, 9-58 guidelines, 8-1 operations, 8-2
patches, 9-58
shoulders, 9-58 temporary repairs, 9-58
Manning's velocity of flow, 6-42
maps geologic, 7-29 soils, 7-29 topographic, 7-29
marginal material, 2-4
mass diagram, 3-19
construction, 3-20
limitations, 3-28
properties, 3-20, 3-21
maximum haul distance, 3-22 metric conversions, A-1
MI. *See* mobility index (MI). middle ordinate, 9-9 mobility index (MI), 7-19
calculating, 7-20
limitations, 7-23
mud con trol. *See* airfield and heliport maintenance, mud control.

multiple surface treatment. *See* surface treatment, multiple.

N

NATO Reference Mobility Model (NRMM), 7-1, 7-26
NRMM. *See* NATO Reference Mobility Model (NRMM).

node, 3-20

0

obstacle crossings, 2-3
obstacles, 7-10, 7-11 off-road speed map, 7-31 Office of the Chief of Engineers, 2-7
one-pass performance, 7-12 open channels. *See also* ditches, types of flow, open channel.

design equations, 6-42
continuity, 6-42
Manning's velocity of flow, 6-42 roughness coefficient (n), 6-42
design factors, 6-38
cross section, 6-38
location, 6-38
open storage area, special considerations, 9-75
organic-soil areas, 7-10

## P

paving, 6-115 peak flow, 6-10
performance categories, 7-19
permafrost, special considerations, 5-15.

See also forest clearing considerations, permafrost and geologic and permafrost conditions.

plank-tread road.

See roads, plank-tread.

planning considerations, 1-1
plastic grid. See sand grid, plastic grids. pending, 6-84
advantages, 6-89
analysis, 6-87
areas, 6-84
potential landing zone, 7-32 precipitation. *See* drainage, hydrology, precipitation, preconstruction phase, 2-1
location factors, 2-1
existing facilities, 2-1 lines of communication (LOC), 2-1 location and design, 2-1
minimum rehabilitation, 2-1 soil characteristics, 2-2
soil investigation prior to construction, 2-2
preswelling, 5-7
prime coat, 9-49
base preparation, 9-49
materials, 9-49

## R

radius of curvature, 9-9
rating cone index (RCI), 7-2, 7-9
rational method of estimating runoff, 6-22
application, 6-28 assumptions, 6-22 estimating flow time for multiple cover, 6-28
estimating flow time for single cover, 6-26
formula, 6-22 formula variables, 6-22
C variable, 6-22
determining TOC, 6-24
I variable, 6-24
time of concentration, 6-24
RCI. See rating cone index (RCI).

reconnaissance, 2-5
air, 2-8 airfield, 2-14, 2-15
air, 2-15 ground, 2-17
airfield-siting template, 2-15, 2-16 briefing, 2-6
engineer, 2-14
existing roads, 2-11 glide-angle requirements, 2-15 ground, 2-8
ground reconnaissance report, 2-19
undeveloped airfield site, 2-19
captured enemy airfield, 2-21
location, 2-11 map and air studies, 2-9 new airfields, 2-15
party, 2-5 personnel suitable, 2-9 planning, 2-6 preliminary study, 2-7 preparation, 4-2
reporting, 2-8
route and road, 2-11
selecting runway location, 2-15 steps, 2-6
referencing point, 3-6
remolding index (RI), 7-1
repair of runways, 8-19
required areas, 2-4
revetments.

See forest clearing considerations, waste areas, revetments, RI, See remolding index (RI).

ripper. See clearing, stripping, and grubbing; clearing with equipment; ripper.

riprap design, 6-118
placement, 6-116 protection, 6-116 size selection, 6-116
road design, 9-1
geometric process, 9-1
grade and alignment, 9-6
road maintenance, 8-9
fords and bridges, 8-16.

See also fords and bridges, patrols, 8-10
repair crews, 8-10 winter, 8-12
snow-removal equipment, 8-13, 8-14
surface ice control, 8-15
with traffic, 8-11.

See also baton method.

road tars, 9-47
roads aggregate-surfaced,
9-62
base course, 9-63 CBR requirements, 9-63
compaction criteria, 9-63
compaction requirements, 9-64
design curves, 9-65 design steps, 9-66
materials, 9-62 select and subbase materials, 9-63
Army track, 9-32
chespaling, 9-31 classes, 9-59
corduroy-surfaced, 9-30
heavy, 9-30
standard, 9-30 types, 9-30
with stringers, 9-30
expedient -surfaced, 9-30 landing mats, 9-32
plank-tread, 9-32 snow and ice, 9-35 unsurfaced, 9-61
wire-mesh, 9-35
Rome plow. *See* clearing, stripping, and grubbing, clearing with equipment; Rome plow.

roughness, 6-77
rubble, 5-15
runoff. See drainage, hydrology, runoff.

## S

safe-slope ratios, 2-2
salts. *See* ice control, salts.

sand grid, 9-36
installation, 9-37 plastic grids, 9-36
scour, types of, 6-73 sediment control, 6-54
segments. *See* entrances, exits, and segments.

select materials, 5-8, 5-9 shoulders and similar areas, 9-75 shrinkage, 3-17
single surface treatment.

See surface treatments, single.

site selection and reconnaissance, 2-1
drainage, 2-2 location factors, 2-1
slipperiness, 7-2, 7-10
slope, 7-10 slope negotiations, 7-11, 7-12
all-wheel-drive vehicles, 7-11
self-propelled vehicles, 7-11 tracked vehicles, 7-11
vehicles towing inoperable, powered vehicles, 7-18 vehicles towing other vehicles, 7-15 vehicles towing trailers, 7-14
snow and ice road. *See* roads, snow and ice.

snow removal.

See airfield and heliport maintenance, snow removal and road maintenance, winter, snow-removal equipment.

soil characteristics.

See drainage-system design, soil characteristics.

soil classification, 5-1, 7-29 soil conditions, mapping manually, 7-30 soil strength, 7-2 soil topography, 7-29 soil trafficability test set, 7-3, E-1
classification, 7-36, 7-37
species of trees and root systems, 4-3 sprayed asphalt with covered-aggregate.

See surface treatments, sprayed aggregate with.

sprayed asphalt with single and multiple surface treatments. *See* surface treatments, sprayed aggregate with.

sprayed treatments, 9-41 St. Anthony Falls Hydraulic Laboratory, 6-125
stabilized chemically, 5-7
mechanically, 5-7
station adjustments, 9-13 stationing equations, 9-13 stakes. *See* construction stakes.

standard rainfall intensity-duration curves, 6-9 standards of trafficability, 2-11 stickiness, 7-2, 7-10
stilling basins.

See erosion control, stilling basins.

storms.

See drainage, hydrology, storms.

strength profile, 7-8
coarse-grained soils, 7-9 fine-grained soils, 7-8 remoldable sands, 7-8
stripping, 9-48 stripping test, 9-48
structural design, 9-27
earth, 9-28
gravel, 9-29
processed materials, 9-30
sand clay, 9-29 stabilized soil, 9-28 treated surface, 9-28
subbase compaction normal cases, 5-6
special cases, 5-6
subbase course, 5-8 subbase materials, 5-9
subgrades, 5-4 subgrade stabilization, 5-7
submerged inlets.

See culverts, design, with submerged inlets, subsurface drainage, 6-92
filter design steps, 6-100
filter material, 6-98
selection, 6-100
pipe-laying criteria, 6-96 system installation, 6-101 techniques, 6-92
blind drabs, 6-94 combination drainage systems, 6-95 deep ditches, 6-92
French drains, 6-94
natural drainage channels, 6-93
subsurface pipe, 6-94
successive areas, 6-33
estimating runoff, 6-34
sunlit slopes, 2-4
superelevation, 9-25 surface treatments, 9-41
covered aggregate, 9-54
multiple, 9-54
requirements, 9-53 single, 9-52 sprayed asphalt with, 9-51
surveys. *See* construction surveys. swell test, 9-48
swelling, 5-7.

See also compaction, swelling soils,

## T

tack coat, 9-50 tactical considerations, 2-5
camouflage, 2-5.

See also forest clearing considerations, camouflage.

defense, 2-5 defilade, 2-5
tangents, 9-6
distance, 9-9
terracing, 6-115
thickness requirements. *See* flexible-pavement structure, bituminous-pavement thickness requirements; unsurfaced soil thickness requirements; and flexible-pavement structure, minimum base-course thickness.

timber cruising, 4-4
lime of concentration (TOC), 6-10. *See also* rational method of estimating runoff, formula variables, time of concentration.

TOC. *See* time of concentration (TOC) and rational method of estimating runoff, formula variables, time of concentration, topography, 2-2.

See also drainage-system design, topographical information and soils topography.

map, 7-29
traffic categories, 9-59
tracked vehicles and forklifts, 9-60
trafficability basic factors, 7-2 characteristics of fine-grained soils and remoldable sand in wet weather, 7-35
classifications of dry-to-moist, coarse-grained soils, 7-38 estimating, 7-27
evaluation factors, 7-10 instruments and tests, 7-3
mapping manually, 7-30
measurements, 7-3, 7-5 photomap, 7-28 procedures in fine-grained soils and remoldable sands, 7-11
standards, 2-11
test data form, 7-7
with weather, 7-2
transition point, 3-20 transpiration, *See* drainage, hydrology, transpiration, tree diameters at breast height (DBH), 4-4
tuff, 5-15
turbulent flow.

See ditches, types of flow, turbulent.

turfing, 6-115

## U

Unified Soil Classification System (USCS), 5-4, unsubmerged inlets.

See culverts, design, with unsubmerged inlets.

unsurfaced roads. *See* roads, unsurfaced.

unsurfaced-soil thickness requirements, 9-62
USCS. *See* Unified Soil Classification System (USCS).

USCS soil-type description, 7-35 utilities, 2-4
UXO. *See* clearing, stripping, and grubbing; removing buried explosives; unexploded ordnance (UXO).

## V

VCI. *See* vehicle cone index (VCI).

VCI determination for new or unlisted vehicles, 7-19 vegetation, 7-10
vehicle classes, 7-19
vehicle cone index (VCI), 7-2
calculating, 7-20, 7-26
limitations, 7-23
velocity relationships, 6-45 vertical alignment, 9-18
volume compacted, 3-17
in-place, 3-17
loose, 3-17 of flow 6-10
volume-determination methods, 3-13
average end area, 3-13 average depth of cut or fill, 3-13
grid, 3-15 prismoldal formula, 3-13
V-type ditch. *See* ditches, V-type.

## W

washboarding, 8-4 watersheds.

See drainage-system design, procedures, delineating watersheds, weather conditions, 7-27
wet season, 7-29
wet-weather trafficability characteristics, 7-35 wier notch, 8-3 windrowing. *See* clearing, stripping, and grubbing; clearing with equipment, windrowing.

wire-mesh road. *See* roads, wire-mesh. witnessing point, 3-6
work, 3-23 world isohyetal map, 6-7
By Order of the Secretary of the Army:
GORDON R. SULLIVAN
Official:
General, United States Army Chief of Staff MILTON H. HAMILTON
Administrative Assistant to the Secretary of the Army
06955
By Order of the Secretary Air Force:
MERRILL A. McPEAK
General United States Air Force Chief of Staff Official:

## Distribution:

Active Army, USAR, and ARNG: To be distributed in accordance with DA Form
12-11E, requirements for FM 5-430-00-1, Vol I, Planning and Design of Roads, Airfields, and Heliports in the Theater of Operations - Road Design (Qty rqr. block no. 0759).