**Subject:** AIRPORT PAVEMENT DESIGN AND **Date:** June 23, 2006 **AC
No:** 150/5320-6D

EVALUATION **Initiated by:** AAS-100 **Change:** 4

**1. PURPOSE.** Advisory Circular (AC) 150/5320-6D, Airport Pavement
Design and Evaluation, has been revised to provide design guidance for
paved airfield shoulders.

**2. PRINCIPAL CHANGES.** Change 4 includes the following:

a.  A new Chapter 8, Pavement Design for Airfield Shoulders, provides
    design guidance for paved runway, taxiway, and apron shoulders.
    Guidance is intended for application on airports accommodating
    Design Group III or larger aircraft.

b.  Revised guidance on required design flexural strength for rigid
    pavement design.

c.  New guidance for rubblization of existing Portland Cement Concrete
    (PCC) pavements prior to asphalt overlay.

d.  Minor corrections to various text and figures.

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DAVID L. BENNETT

Director of Airport Safety and Standards

605\. APPLICATION OF RIGID PAVEMENT EVALUATION PROCEDURES 139

606\. USE OF RESULTS 139

607\. REPORTING PAVEMENT STRENGTH 139

**CHAPTER 7. Layered Elastic Pavement Design**

**Section 1. Design Considerations 141**

701\. Purpose 141

702\. Application 141

703\. Background 141

704\. Computer program 141

705\. pavement design considerations 142

706\. FLEXIBLE PAVEMENT dESIGN 142

707\. RIGID PAVEMENT DESIGN 143

708\. Layered Elastic oVERLAY DESIGN 144

TABLE 7-1. RIGID PAVEMENT DISTRESS TYPES USED TO CALCULATE

THE STRUCTURAL CONDITION INDEX, SCI 145

**CHAPTER 8. Pavement Design For Airfield Shoulders**

801\. Purpose 147

802\. Application 147

803\. Background 147

804\. Purpose of Design Procedure 147

805\. Design procedure 147

806\. PAVEMENT LAYER THICKNESS AND MATERIAL REQUIREMENTS 148

807\. EMERGENCY AND MAINTENANCE VEHICLE CONSIDERATIONS. 148

808\. AREAS SUSCEPTIBLE TO FROST HEAVE 149

**APPENDIX 1. ECONOMIC ANALYSIS 1**

1\. BACKGROUND 1

2\. ANALYSIS METHOD 1

3\. STEP BY STEP PROCEDURE 1

4\. EXAMPLE PROBLEM - LIGHT-LOAD GENERAL AVIATION AIRPORT 2

TABLE 1. COSTS OF REHABILITATION ACTIVITIES 4

TABLE 3. SUMMARY OF ALTERNATIVES 5

TABLE 4. COMPARATIVE RANKING OF ALTERNATIVES 5

5\. SUMMARY 5

**APPENDIX 2. DEVELOPMENT OF PAVEMENT DESIGN CURVES 1**

1\. BACKGROUND 1

TABLE 1. SINGLE WHEEL ASSEMBLY 1

TABLE 2. DUAL WHEEL ASSEMBLY 1

TABLE 3. DUAL TANDEM ASSEMBLY 1

2\. RIGID PAVEMENTS 1

TABLE 4. PASS-TO-COVERAGE RATIOS FOR RIGID PAVEMENTS 2

FIGURE 1. ASSEMBLY POSITIONS FOR RIGID PAVEMENT ANALYSIS 3

FIGURE 2. PERCENT THICKNESS VS. COVERAGES 4

3\. FLEXIBLE PAVEMENTS 5

TABLE 5. PASS-TO-COVERAGE RATIOS FOR FLEXIBLE PAVEMENTS 5

FIGURE 3. LOAD REPETITION FACTOR VS. COVERAGES 6

**APPENDIX 3. DESIGN OF STRUCTURES FOR HEAVY AIRCRAFT 1**

1\. BACKGROUND 1

2\. RECOMMENDED DESIGN PARAMETERS 1

FIGURE 1. TYPICAL GEAR CONFIGURATIONS FOR DESIGN OF

STRUCTURES 2

**APPENDIX 4. RELATED READING MATERIAL 1**

**APPENDIX 5. AIRFIELD PAVEMENT DESIGN SOFTWARE 1**

\(1\) Total Pavement Thickness Unstabilized. Enter Figure 3-4 with the
subgrade CBR value of 7 and read a total pavement thickness of 37.5
inches (953 mm). This thickness includes surfacing, granular base
(P-209) and granular subbase (P-154)

\(2\) Thickness of Base and Surface Unstabilized. Re-enter Figure 3-4
with the assumed subbase CBR (P-154) of 20 (see paragraph 321 b.) and
read a thickness of 17.0 inches (432 mm). This thickness includes
surfacing and granular base (P-209). The note on Figure 3-4 states that
the thickness of surfacing for critical areas is 4 inches (100 mm).

\(3\) Unstabilized Section. The unstabilized section would thus consist
of 4 inches (100 mm) of surfacing, 13 inches (330 mm) of granular base
(P-209) and 20 l/2 inches (520 mm) of granular subbase (P-154). (4)
Stabilized Base Thickness. Assume the equivalency factor for P-401 base
material to be 1.4. The required thickness of stabilized base is
determined by dividing the thickness of granular base calculated in step
(3) above by the equivalency factor. In this example 13 inches (330 mm)
would be divided by 1.4 yielding 9 inches (230 mm).

\(5\) Stabilized Subbase Thickness. Referring to Table 3-7, assume the
equivalency factor for P-401 used as subbase is 2.0. Divide the
thickness of granular subbase 20 l/2 inches (520 mm) by 2.0 which yields
10 inches (255 mm) of P-401 subbase.

\(6\) Stabilized Section. The stabilized section would be 4 inches (100
mm) of surfacing, 9 inches (230 mm) of stabilized base (P-401) and 10
inches (255 mm) of stabilized subbase (P-401).

\(7\) Check Minimum Thickness. The total pavement thickness given above
4 + 9 + 10 = 23 inches (585 mm) is then compared to the total pavement
thickness required for a CBR of 20. This was done in step (2) above and
gave a thickness of 17.0 inches (430 mm). Since the calculated thickness
of 23 inches (585 mm) is larger than the CBR=20 minimum thickness of 17
inches (430 mm), the design is adequate. Had the CBR=20 thickness
exceeded the calculated thickness, the subbase thickness would have been
increased to make up the difference.

322\. FULL-DEPTH ASPHALT PAVEMENTS. Full-depth asphalt pavements contain
asphaltic cement in all components above the prepared subgrade. The
design of full-depth asphalt pavements can be accomplished using the
equivalency factors presented in paragraph 321 and illustrated in
paragraph 321f. Manual Series No. 11 prepared by the Asphalt Institute,
dated January 1973, can also be used to design full-depth asphalt
pavements when approved by the FAA.

323\. FROST EFFECTS. Frost protection should be provided in areas where
conditions conductive to detrimental frost action exist. Levels of frost
protection are given in paragraph 308b of this document. Frost
considerations may result in thicker subbase courses than the
thicknesses needed for structural support.

a\. Example. An example of pavement design for seasonal frost follows.
Assume the same design conditions as in paragraph 321f above.

\(1\) Structural Requirements. The structural requirements for the
example are: 4 inches (100 mm) of surfacing, 9 inches (230 mm) of
stabilized base, and 10 inches (255 mm) of stabilized subbase. This
section provides a total pavement thickness of 23 inches (585 mm).

\(2\) Determine Soil Frost Group. Assume the subgrade soil is a clayey
sand SC with 10% of the material finer than 0.02 mm. The unit dry weight
of the subgrade soil is 115 pcf (184 kg/cu m). The soil frost group is
found in Table 2-4 and in this example is FG-2.

\(3\) Determine the Depth of Frost Penetration. The design air freezing
index for the area is 350 degree days. Referring to figure 2-6 the depth
of frost penetration is found to be 28 inches.

\(4\) Types of Frost protection. Several levels of frost protection are
possible as follows:

\(i\) Complete Frost Protection. Complete frost protection would require
the pavement section be increased from 23 inches (585 mm) to 28 inches
(710 mm). This would require placing 5 inches (125 mm) of nonfrost
susceptible material beneath the structural section.

\(ii\) Limited Frost Protection. Limited subgrade frost penetration
provides nonfrost susceptible material to a depth of 65% of the depth of
frost penetration. In this example, 65% of 28 inches (710 mm) equals 18
inches (460 mm). Since the structural design section provides a total
pavement thickness of 23 inches (585 mm), no further protection is
required. The structural section provides more than enough protection to
satisfy the limited subgrade frost penetration requirements.

\(iii\) Reduced Subgrade Strength. The reduced subgrade strength rating
for an FG-2 soil is found in paragraph 308a.(3) and is a CBR of 7. Since
the design CBR used in the example was 7, the structural design is
adequate for the reduced subgrade strength method of frost protection.
As has been previously mentioned, this method is intended to provide
adequate structural support when the frost is melting.

\(5\) Summary. In summary, for areas sensitive to pavement heave due to
frost action the complete protection method should be used. This would
add 4 inches (100 mm) of nonfrost susceptible material to the structural
section. In areas where some degree of pavement heave due to frost
action can be tolerated, the structural section will be adequate. The
same is true for providing structural support during periods of frost
melting, i.e. the structural section is adequate.

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FIGURE 3-16 EFFECT OF STABILIZED SUBBASE ON SUBGRADE MODULUS

# 331. DETERMINATION OF CONCRETE SLAB THICKNESS. Design curves have been prepared for rigid pavements similar to those for flexible pavements; i.e., separate curves for a variety of landing gear types and aircraft. See Figures 3-17 through 3-29. These curves are based on a jointed edge loading assumption where the load is located either tangent or perpendicular to the joint. Use of the design curves requires four design input parameters: concrete flexural strength, subgrade modulus, gross weight of the design aircraft, and annual departure of the design aircraft. The rigid pavement design curves indicate the thickness of concrete only. Thicknesses of other components of the rigid pavement structure must be determined separately.

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a\. Concrete Flexural Strength. The required thickness of concrete
pavement is related to the strength of the concrete used in the
pavement. Concrete strength is assessed by the flexural strength, as the
primary action of a concrete pavement slab is flexure. Concrete flexural
strength should be determined by ASTM C 78 test method. The design
flexural strength of the concrete should be based on the age and
strength the concrete will be required to have when it is scheduled to
be opened to traffic. Thickness design strength of 600 to 650 psi is
recommended for most airfield applications. Unless expedited
construction is required, the strength specified for material acceptance
during construction should be specified as a 28 day strength and be 5
percent less than the strength used for thickness design.

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#  b. k Value. The k value is in effect, a spring constant for the material supporting the rigid pavement and is indicative of the bearing capacity of the supporting material.

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#  c. Gross Weight of Design Aircraft. The gross weight of the design aircraft is shown on each design curve. The design curves are grouped in accordance with either main landing gear assembly type or as separate curves for individual aircraft. A wide range of gross weights is shown on all curves to assist in any interpolations which may be required. In all cases, the range of gross weights shown is adequate to cover weights of the aircraft represented.

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#  d. Annual Departures of Design Aircraft. The fourth input parameter is annual departures of the design aircraft. The departures should be computed using the procedure explained in paragraph 305.

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# 332. USE OF DESIGN CURVES.

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#  a. Rigid Pavement Design Curves. The rigid pavement design curves are constructed such that the design inputs are entered in the same order as they are discussed in paragraph 331. Dashed "chase around lines" are shown on the curves to indicate the order of progression through the curves. Concrete flexural strength is the first input. The left ordinate of the design curve is entered with concrete flexural strength. A horizontal projection is made until it intersects with the appropriate foundation modulus line. A vertical projection is made from the intersection point to the appropriate gross weight of the design aircraft. A horizontal projection is made to the right ordinate showing annual departures. The pavement thickness is read from the appropriate annual departure line. The pavement thickness shown refers to the thickness of the concrete pavement only, exclusive of the subbase. This thickness is that shown as "T" in Figure 3-1, referred to as the critical thickness.

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#  b. Optional Design Curves. When aircraft loadings are applied to a jointed edge, the angle of the landing gear relative to the jointed edge influences the magnitude of the stress in the slab. Single wheel and dual wheel landing gear assemblies produce the maximum stress when the gear is located parallel or perpendicular to the joint. Dual tandem assemblies often produce the maximum stress when positioned at an acute angle to the jointed edge. Figures 3-30 through 3-41, have been prepared for dual tandem gears located tangent to the jointed edge but rotated to the angle causing the maximum stress. These design curves can be used to design pavement in areas where aircraft are likely to cross the pavement joints at acute angles such as runway holding aprons, runway ends, runway-taxiway intersections, aprons, etc. Use of Figures 3-30 through 3-41 is optional and should only be applied in areas where aircraft are likely to cross pavement joints at an acute angle and at low speeds.

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# 333. CRITICAL AND NONCRITICAL AREAS. The design curves, Figures 3-17 through 3-41, are used to determine the concrete slab thickness for the critical pavement areas shown as "T" in Figure 3-l. The 0.9T thickness for noncritical areas applies to the concrete slab thickness. For the variable thickness section of the thinned edge and transition section, the reduction applies to the concrete slab thickness. The change in thickness for the transitions should be accomplished over an entire slab length or width. In areas of variable slab thickness, the subbase thickness must be adjusted as necessary to provide surface drainage from the entire subgrade surface. For fractions of an inch of 0.5 or more, use the next higher whole number; for less than 0.5, use the next lower number.

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height="7.926388888888889in"}

FIGURE 3-44 JOINTING OF REINFORCED RIGID PAVEMENTS

**348. CONTINUOUSLY REINFORCED CONCRETE PAVEMENT**. A continuously
reinforce concrete pavement (CRCP) is a Portland cement concrete
pavement with continuous longitudinal steel reinforcement and no
intermediate transverse expansion or contraction joints. Continuously
reinforced concrete pavements normally contain from 0.5 to 1.0 percent
longitudinal steel reinforcement. The main advantage of continuously
reinforced concrete pavement is the elimination of transverse joints
which are costly to construct, require periodic resealing, and are often
a source of maintenance problems. Continuously reinforced concrete
pavements usually provide a very smooth riding surface. A properly
designed CRCP will develop random transverse cracks at 2 to 10 feet (0.6
to 3 m) intervals. The resultant pavement is composed of a series of
articulated short slabs held tightly together by the longitudinal
reinforcing steel. A high degree of shear transfer across the cracks can
be achieved because the cracks are held tightly closed.

**a. Foundation Support.** The reinforcing steel in a CRCP provides
continuity of load transfer however good uniform foundation support must
still be provided for satisfactory performance. The embankment and
subbase requirements given earlier in this Chapter for plain concrete
pavements also apply to CRCP.

**b. Thickness Design.** The thickness requirements for CRCP are the
same as plain concrete and are determined from the appropriate design
curves, Figures 3-17 through 3-41. Design inputs are the same for
concrete strength, foundation strength, aircraft weight and departure
level.

**c. Longitudinal Steel Design.** The design of steel reinforcement for
CRCP is critical to providing a satisfactory pavement. The steel
percentage must be properly selected to provide optimum crack spacing
and crack width. Crack widths must be small to provide a high degree of
shear transfer across the crack and to prevent the ingress of water
through the crack. The design of longitudinal steel reinforcement must
satisfy three conditions. The maximum steel percentage determined by any
of the three following requirements should be selected as the design
value. In no case should the longitudinal steel percentage be less than
0.5 percent.

**(1) Steel to Resist Subgrade Restraint.** The longitudinal steel
reinforcement required to resist the forces generated by the frictional
restraint between the CRCP and the subbase should be determined by using
the nomograph shown on Figure 3-45. Use of the nomograph requires three
parameters: allowable working stress for steel, tensile strength of
concrete and a friction factor for the subbase. The recommended working
stress for steel is 75 percent of the specified minimum yield strength.
The tensile strength of concrete may be estimated as 67 percent of the
flexural strength. The recommended friction factor for stabilized
subbase is 1.8. While not recommended as subbase for CRCP, friction
factors for unbound fine-grained soils and coarse-grained soils are
usually assumed to be 1.0 and 1.5 respectively.

**(2) Steel to Resist Temperature Effects.** The longitudinal steel
reinforcement must be capable of withstanding the forces generated by
the expansion and contraction of the pavement due to temperature
changes. The following formula is used to compute the temperature
reinforcement requirements.

$P_{S} = \frac{\text{50f}_{S}}{f_{S} - \text{195}T}$

where:

P~s~ = steel reinforcement in percent

f ~t~ = tensile strength of concrete

f ~s~ = working stress for steel usually taken as 75% of specified
minimum yield strength

T = maximum seasonal temperature differential for pavement in degrees
Fahrenheit

Reinforcing steel should be specified on the basis of minimum yield
strength. All deformed reinforcing steel bars should conform to ASTM A
615, A 616 or A 617. Deformed welded wire fabric should conform to ASTM
A 497.

**(2) Increasing C~b~ Factor.** A value of C~b~ lower than 0.75
represents a severely cracked base slab, which would not be advisable to
overlay without modification due to the likelihood of severe reflection
cracking. See paragraph 406 f. In some instances it may be advantageous
to replace several slabs and restore load transfer along inadequate
joints to raise the C~b~ value. Increasing the C~b~ value will decrease
the required overlay thickness. A detailed condition survey of the
existing pavement which examines the subsurface drainage conditions,
structural capacity of the slabs, foundation strength, flexural strength
of the concrete, load transfer along joints and thickness of the
component layers is strongly encouraged to properly design a hot mix
asphalt overlay.

**c. Example.** An example of the hot mix asphalt overlay design method
is given below:

**(1) Assumptions**. Assume an existing rigid pavement 12 inches (305
mm) thick is to be strengthened to accommodate 3000 departures of a dual
wheel aircraft weighing 180,000 pounds (81,800 kg). The flexural
strength of the existing concrete is 725 psi (5.00 MN/m') and the
foundation modulus is 300 pci (81.6 MN/m'). The condition factor of the
existing pavement is 0.95.

**(2) Single Slab Thickness.** Compute the single slab thickness
required to satisfy the design conditions given in (1) above. Using
Figure 3-17 the slab thickness is found to be 13.9 inches (353 mm). The
F factor is determined from Figure 4-3 and equals 0.93. Applying the
overlay formula given in paragraph 406 yields:

t =2.5 (0.93 x13.9 - 0.95 x12)

t = 3.82 inches (97 mm)

This thickness would be rounded up to 4 inches (100 mm) for practicality
of construction.

**d. Previously Overlaid Rigid Pavement.** The design of a hot mix
asphalt overlay for a rigid pavement which already has an existing hot
mix asphalt overlay is slightly different. The designer should treat the
problem as if the existing hot mix asphalt overlay were not present,
calculate the overlay thickness required, and then adjust the calculated
thickness to compensate for the existing overlay. If this procedure is
not used, inconsistent results will often be produced.

**e.** **Example.** An example of a hot mix asphalt overlay design for a
rigid pavement which already has an existing hot mix asphalt overlay is
given below:

**(1) Assumptions.** An example of the procedure follows. Assume an
existing pavement consists of a 10-inch (255 mm) rigid pavement with a
3-inch (75 mm) hot mix asphalt overlay. The existing pavement is to be
strengthened to be equivalent to a single rigid pavement thickness of 14
inches (355 mm). Assume an "F" factor of 0.9 and "C~b~" of 0.9 are
appropriate for the existing conditions.

**(2) Ignore Existing Overlay.** Calculate the required thickness of hot
mix asphalt overlay as if the existing 3-inch (75 mm) overlay were not
present.

t = 2.5 (0.9 xl4 - 0.9 x10)

t = 9 inches (230 mm)

**(3) Thickness Allowance For Existing Overlay**. An allowance is then
made for the existing hot mix asphalt overlay. In this example assume
the existing overlay is in such a condition that its effective thickness
is only 2.5 inches (64 mm). The required overlay thickness would then be
9 - 2.5 = 6.5 inches (165 mm). The determination of the effective
thickness of the existing overlay is a matter of engineering judgment.

**f. Limitations.** The formula for hot mix asphalt overlay thickness
assumes the existing rigid pavement will support load through flexural
action. As the overlay thickness becomes greater, at some point the
existing rigid pavement will tend to act more like a high quality base
material. When this condition is reached, the overlay should be designed
as a flexible pavement with the existing pavement treated as a high
quality base course.

**407. NONSTRUCTURAL HOT MIX ASPHALT OVERLAYS.** In some instances
overlays are required to correct nonstructural problems such as
restoration of crown, improve rideability, etc. Thickness calculations
are not required in these situations, as thickness is controlled by
other design considerations or minimum practical overlay thickness.
Information concerning runway roughness correction can be found in FAA
Report No. FAA-RD-75-110, Methodology for Determining, Isolating and
Correcting Runway Roughness. See Appendix 4.

**408. REFLECTION CRACKING IN HOT MIX ASPHALT OVERLAYS.** Reflection
cracking is often a problem in hot mix asphalt overlays particularly
overlays of rigid pavement. Numerous materials and techniques have been
tried attempting to solve the problem with varying degrees of success.
The following methods have met with some success:

**a. Coarse Aggregate Binders.** The use of coarse aggregate binder
course is recommended where economically feasible. Use of the largest
practical size coarse aggregate in the hot mix asphalt layer immediately
above the existing pavement is recommended. This practice provides some
measure of protection against reflection cracking.

**b. Rubblization of Existing PCC Pavement.** If the condition of the
existing rigid pavement is very poor (i.e., extensive structural
cracking, joint faulting, "D" cracking, etc.), consideration may be
given to using the "rubblization" technique. Subgrade support conditions
must be considered, as weak subgrade support can cause difficulties in
rubblizing the existing pavement and cause premature failures in the
completed pavement. Rubblization involves purposely breaking the
existing rigid pavement into small pieces and then rolling the broken
pieces to firmly seat them in the foundation. A hot mix asphalt layer is
then placed over the pavement. This type of section is designed as a
flexible pavement, treating the broken rigid pavement as base course.
Reflective cracking is reduced or eliminated with this type of
construction.

**c. Engineering Fabrics.** Research studies and field performance have
shown that fabric membranes are effective in retarding reflection
cracking. While fabrics will not eliminate reflection cracking all
together, they do provide some degree of water-proofing beneath
reflection cracks thus protecting the existing pavement and foundation.
At present, the water-proofing capability of fabrics, assuming the
capacity of the asphalt impregnated fabric to resist rupture is not
lost, appears to be the most significant contribution fabrics provide in
a hot mix asphalt overlay system. Existing pavements, whether flexible
or rigid, that show evidence of excessive deflections, substantial
thermal stresses, and/or poor drainage, probably will exhibit no
improvement by including a fabric in a structural overlay. The following
conditions are recommended for fabric usage:

**(1) Fabric Properties**. The fabric should have a minimum tensile
strength of 90 lbs (41 kg) when tested in accordance with ASTM D 4632
and a density in the range of 3 to 5.5 ounces per square yard (70 to 130
grams per square meter).

**(2) Application.** Fabric membranes should not be used where the
horizontal displacements exceed 0.05 inch (1.3 mm) or where vertical
displacements will exceed 0.02 inch (0.5 mm). Fabric should not be used
when the overlay thickness is less than 3 inches (75 mm) or more than 7
inches (178 mm).

**(3) Tack Coat**. The proper amount of tack coat applied to the fabric
is critical. Emulsified asphalt applied at a rate of from 0.15 to 0.30
gallons per square yard (0.7 to 1.4 liters per square meter) is
recommended. The optimum amount of tack coat will depend on the type of
fabric and the surface on which the fabric is placed.

**d. Asphalt Reinforcement.** Destructive tensile stresses in asphalt
pavements may be reduced by incorporating a reinforcement material.
Reinforcement materials are similar to fabric membranes except the
reinforcement is either a woven fabric or a grid- shaped material. These
materials have very high tensile strength and very low strain capacity.
Products with a combination of fabric materials and reinforcement grids
have been developed and appear to be successful in retarding reflective
cracking. Depending upon the material type and the intended purpose,
reinforcing materials may be applied across the full width of the
pavement or may be limited to the immediate area around joints and
cracks.

**409. DESIGN OF CONCRETE OVERLAYS.** Concrete overlays can be
constructed on existing rigid or flexible pavements. The minimum
allowable thickness for concrete overlays is 5 inches (127 mm) when
placed on a flexible pavement, directly on a rigid pavement, or on a
leveling course. The minimum thickness of concrete overlay which is
bonded to an existing rigid pavement is 3 inches (75 mm). The design of
concrete overlays is based on a thickness deficiency approach. The
existing base pavement and overlay section are equated to a single slab
thickness. The empirical formulas presented were developed from research
on test track pavements and observations of in-service pavements.

# 

# CHAPTER 8. PAvement Design For Airfield Shoulders

**801. PURPOSE.** This chapter provides a design procedure for paved
airfield shoulders.

**802. APPLICATION.** The design procedure for paved or surfaced
shoulders applies to all airports that accommodate Design Group III or
higher aircraft.

**803. BACKGROUND.** The need for paved or surfaced shoulders is created
due to erosion and generation of debris from jet blast. As aircraft grew
in size, so did the size of the aircraft engines and their respective
increase in jet thrust or jet blast. Jet blast can cause problems with
erosion of unprotected soil immediately adjacent to airfield pavements.
To mitigate this problem, FAA recommends paved shoulders for runways,
taxiway, and aprons that will accommodate Group III and higher aircraft.
In addition to providing protection from jet blast, the shoulder must be
capable of safely supporting "occasional" passage of the most demanding
aircraft as well as emergency and maintenance vehicles.

**804. Purpose of Design Procedure.** The procedure for shoulder
pavement thickness design is intended to provide a minimum pavement
structure to support limited operations of aircraft. The design is
intended to provide sufficient support for unintentional or emergency
operations of an aircraft on the shoulder pavement. Use standard
airfield pavement design requirements to design all areas of pavement
where aircraft regularly operate.

The minimum section provided by the shoulder pavement design procedure
will not perform in the same fashion as full strength airfield
pavements. The shoulder pavement is intended to allow safe operation of
the aircraft across the paved area without damage to the aircraft.
Flexible shoulder pavement sections may experience noticeable vertical
movements with each passage of an aircraft and may require inspection
and/or limited repair after each operation. Rigid shoulder pavement
sections may experience cracking with each operation.

**805. DESIGN PROCEDURE.** The design procedure is based upon the FAA
Layered Elastic pavement design software (LEDFAA) and utilizes a
modified design procedure to determine the most demanding aircraft (MDA)
for shoulder pavement design purposes. Several of the procedural
assumptions in the standard pavement design (traffic distribution,
pass-to-coverage ratios, etc,) are not valid and are not used for the
shoulder pavement design procedure. The procedure determines the minimum
pavement section required for the MDA, assuming a total of 10
departures. A composite traffic mixture is not considered for the
shoulder design.

The shoulder pavement design procedure determines the MDA by calculating
pavement thickness requirements for all aircraft utilizing or expected
to utilize the airport. The aircraft requiring the thickest pavement
section is considered the MDA. The following steps are used to complete
the design procedure:

> 1 Use the LEDFAA software to create a new job file and proposed
> pavement section for the shoulder design. Include all desired pavement
> layers, e.g. surface course, base course, stabilized course, subbase
> course, etc. Adjust layer thickness to observe minimum thickness
> requirements for shoulder design.
>
> NOTE: Due to minimum pavement layer requirements in the formal
> airfield pavement design procedure, it may be necessary to use the
> "undefined" pavement layer to represent the proposed shoulder pavement
> cross-section.
>
> 2 Input one aircraft from the traffic mixture for analysis.
>
> a\. Adjust aircraft operating weights as appropriate.
>
> b\. Change annual departures to 1.0 departure.
>
> 3 Return to the Structure screen and confirm that the design period is
> 10 years.
>
> NOTE: The intent of this design procedure is to design a pavement for
> 10 total departures of the most demanding aircraft. By setting annual
> departures to 1 and the design period to 10, the total departures is
> 10.
>
> 4 Confirm the composition and thickness of pavement layers and that
> the correct layer is designated for thickness iteration. The iteration
> layer will be shown with a small arrow along the left side.
>
> 5 Click on the "Design Structure" button to establish the minimum
> pavement section for the individual aircraft.
>
> 6 Repeat steps 1 through 5 for all aircraft in the traffic mixture.
> The pavement section with the greatest thickness requirement is the
> design for the shoulder pavement.
>
> EVALUATION AID: To reduce the list of individual aircraft requiring
> evaluation, include all aircraft from the airport traffic mixture and
> set annual departures of all aircraft to 1,200 annual departures.
> Create the proposed shoulder pavement section in the structure screen,
> then click the "Life" button instead of the "Design Structure" button.
> Return to the aircraft mixture, and scroll over to the column labeled
> "CDF Max for Aircraft". The aircraft with the highest CDF Max value
> will be the most demanding aircraft in most instances and will control
> the shoulder design. However, the top few aircraft with the highest
> CDF Max values should be evaluated because the thickness of the
> pavement section being evaluated will influence which aircraft is the
> most demanding.

**806. Pavement Layer Thickness and Material Requirements.**

**a. Asphalt Surface Course Materials.** The minimum recommended
thickness for asphalt surfacing material is 3 inches. The material
should be of high quality, similar to FAA Item P-401, and compacted to
an average target density of 94 percent of maximum theoretical density.
Material produced for use with high traffic volume highway pavement is
acceptable provided the compaction specified for the highway application
is obtained.

**b. Portland Cement Concrete Surface Course Materials.** The minimum
recommended thickness for rigid pavement design is 6 inches. Portland
Cement Concrete (PCC) must be a high quality, durable material capable
of resisting deterioration due to environmental factors. The PCC should
be similar to FAA Item P-501, with a minimum design flexural strength of
600 psi. Material produced for use with high traffic volume highway
pavement is acceptable provided that environmental durability is
addressed.

**b. Base Course Materials.** Base course materials must be high quality
crushed stone or stabilized materials similar to FAA Items P-208, P-209,
P-301, or P-304. Materials produced for use with high traffic volume
highway pavement may be acceptable provided they possess qualities
similar to the FAA specification items. Crushed stone material must
possess a minimum CBR value of 80. The recommended minimum thickness of
the base course material is 6 inches. The minimum base course thickness
may be reduced to 4 inches by increasing the minimum asphalt thickness
by 1.0 inch. Place base course material in accordance with the
appropriate standard from AC 150/5370-10 or in accordance with the
applicable State Highway standard. Additional consideration should be
given to frost heave susceptibility of the material when used in
frost-susceptible zones.

**c. Subbase Course Materials.** Subbase course material must provide a
minimum CBR value of 20. Materials produced by State Highway standards
are acceptable provided the minimum CBR value is obtained. Place subbase
course material in accordance with AC 150/5370-10, Item P-154 or in
accordance with the applicable State Highway standard. Additional
consideration should be given to frost heave susceptibility of the
material when used in frost susceptible zones. The minimum recommended
thickness is 4 inches. See paragraph 808 below.

**d. Subgrade Materials.** Preparation of subgrade materials should be
in accordance with AC 150/5370-10, Item P-152.

**807. EMERGENCY AND MAINTENANCE VEHICLE CONSIDERATIONS.** In most
cases, the pavement design selected by the shoulder design procedure
should provide sufficient strength for unlimited operations of
maintenance and emergency vehicles. If high operations of these vehicles
are anticipated, the shoulder design should be verified for the
anticipated service.

**808. AREAS SUSCEPTIBLE TO FROST HEAVE.** In areas prone to frost
heave, it may be necessary to increase the thickness of the shoulder
pavement to avoid differential frost heave. Additional thickness of the
pavement beyond that necessary for structural design may be achieved
with any material suitable for pavement construction. The material
should possess a CBR value higher than the subgrade and have non-frost
susceptible properties. Place the additional layer immediately on the
subgrade surface below all base and subbase layers.

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