### **ITEM P-154 SUBBASE COURSE**

DESCRIPTION

**154-1.1**  This item shall consist of a subbase course composed of
granular materials constructed on a prepared subgrade or underlying
course in accordance with these specifications, and in conformity with
the dimensions and typical cross section shown on the plans.

MATERIALS

**154-2.1 MATERIALS.**  The subbase material shall consist of hard
durable particles or fragments of granular aggregates.  This material
will be mixed or blended with fine sand, clay, stone dust, or other
similar binding or filler materials produced from approved sources. 
This mixture must be uniform and shall comply with the requirements of
these specifications as to gradation, soil constants, and shall be
capable of being compacted into a dense and stable subbase.  The
material shall be free from vegetable matter, lumps or excessive amounts
of clay, and other objectionable or foreign substances.  Pit‑run
material may be used, provided the material meets the requirements
specified.

**TABLE 1. GRADATION REQUIREMENTS**

+-------------------------------+--------------------------------------+
| **Sieve designation (square   | **Percentage by weight passing       |
| openings)**                   | sieves**                             |
+-------------------------------+--------------------------------------+
| **as per ASTM C 136 and ASTM  |                                      |
| D 422**                       |                                      |
+-------------------------------+--------------------------------------+
|                               |                                      |
+-------------------------------+--------------------------------------+
| > 3 inch (75.0 mm)            | 100                                  |
+-------------------------------+--------------------------------------+
| > No. 10 (2.0 mm)             | 20‑100                               |
+-------------------------------+--------------------------------------+
| > No. 40 (0.450 mm)           | 5‑60                                 |
+-------------------------------+--------------------------------------+
| > No. 200 (0.075 mm)          | 0‑8                                  |
+-------------------------------+--------------------------------------+

The portion of the material passing the No. 40 (0.450 mm) sieve shall
have a liquid limit of not more than 25 and a plasticity index of not
more than 6 when tested in accordance with ASTM D 4318.

The maximum amount of material finer than 0.02 mm in diameter shall be
less than 3%.

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> **Include testing frequencies for the particle size distribution for
> preliminary and minimum of one per day during construction.**

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CONSTRUCTION METHODS

**154-3.1 GENERAL.**  The subbase course shall be placed where
designated on the plans or as directed by the Engineer.  The material
shall be shaped and thoroughly compacted within the tolerances
specified.

Granular subbases which, due to grain sizes or shapes, are not
sufficiently stable to support without movement the construction
equipment, shall be mechanically stabilized to the depth necessary to
provide such stability as directed by the Engineer.  The mechanical
stabilization shall principally include the addition of a fine‑grained
medium to bind the particles of the subbase material sufficiently to
furnish a bearing strength, so that the course will not deform under the
traffic of the construction equipment.  The addition of the binding
medium to the subbase material shall not increase the soil constants of
that material above the limits specified.

**154-3.2 OPERATION IN PITS.**  All work involved in clearing and
stripping pits and handling unsuitable material encountered shall be
performed by the Contractor at his/her own expense.  The subbase
material shall be obtained from pits or sources that have been
approved.  The material in the pits shall be excavated and handled in
such manner that a uniform and satisfactory product can be secured.

**154-3.3 PREPARING UNDERLYING COURSE.**  Before any subbase material is
placed, the underlying course shall be prepared and conditioned as
specified.  The course shall be checked and accepted by the Engineer
before placing and spreading operations are started.

To protect the subgrade and to ensure proper drainage, the spreading of
the subbase shall begin along the centerline of the pavement on a
crowned section or on the high side of pavements with a one‑way slope.

**154-3.4 MATERIALS ACCEPTANCE IN EXISTING CONDITION.**  When the entire
subbase material is secured in a uniform and satisfactory condition and
contains approximately the required moisture, such approved material may
be moved directly to the spreading equipment for placing.  The material
may be obtained from gravel pits, stockpiles, or may be produced from a
crushing and screening plant with the proper blending.  The materials
from these sources shall meet the requirements for gradation, quality,
and consistency.  It is the intent of this section of the specifications
to secure materials that will not require further mixing.  The moisture
content of the material shall be approximately that required to obtain
maximum density.  Any minor deficiency or excess of moisture may be
corrected by surface sprinkling or by aeration.  In such instances, some
mixing or manipulation may be required, immediately preceding the
rolling, to obtain the required moisture content.  The final operation
shall be blading or dragging, if necessary, to obtain a smooth uniform
surface true to line and grade.

**154-3.5 PLANT MIXING.**  When materials from several sources are to be
blended and mixed, the subbase material shall be processed in a central
or travel mixing plant.  The subbase material, together with any blended
material, shall be thoroughly mixed with the required amount of water. 
After the mixing is complete, the material shall be transported to and
spread on the underlying course without undue loss of the moisture
content.

**154-3.5.1 MIXED IN PLACE.**  When materials from different sources are
to be proportioned and mixed or blended in place, the relative
proportions of the components of the mixture shall be as designated by
the Engineer.

The subbase material shall be deposited and spread evenly to a uniform
thickness and width.  Then the binder, filler or other material shall be
deposited and spread evenly over the first layer.  There shall be as
many layers of materials added as the Engineer may direct to obtain the
required subbase mixture.

When the required amount of materials have been placed, they shall be
thoroughly mixed and blended by means of graders, discs, harrows, rotary
tillers, supplemented by other suitable equipment if necessary.  The
mixing shall continue until the mixture is uniform throughout.  Areas of
segregated material shall be corrected by the addition of binder or
filler material and by thorough remixing.  Water in the amount and as
directed by the Engineer shall be uniformly applied prior to and during
the mixing operations, if necessary, to maintain the material at its
required moisture content.  When the mixing and blending has been
completed, the material shall be spread in a uniform layer which, when
compacted, will meet the requirements of thickness and typical cross
section.

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> **If mixing in place will not provide a consistent subbase material,
> delete paragraph 154-3.5.1.**

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**154-3.6 GENERAL METHODS FOR PLACING.**  The subbase course shall be
constructed in layers.  Any layer shall be not less than 3 inches (75
mm) nor more than 8 inches (200 mm) of compacted thickness.  The subbase
material shall be deposited and spread evenly to a uniform thickness and
width. The material, as spread, shall be of uniform gradation with no
pockets of fine or coarse materials.  The subbase, unless otherwise
permitted by the Engineer, shall not be spread more than 2,000 square
yards (1700 square meters) in advance of the rolling.  Any necessary
sprinkling shall be kept within this limit.  No material shall be placed
in snow or on a soft, muddy, or frozen course.

When more than one layer is required, the construction procedure
described herein shall apply similarly to each layer.

During the placing and spreading, sufficient caution shall be exercised
to prevent the incorporation of subgrade, shoulder, or foreign material
in the subbase course mixture.

**154-3.7 FINISHING AND COMPACTING.**  After spreading or mixing, the
subbase material shall be thoroughly compacted by rolling and
sprinkling, when necessary.  Sufficient rollers shall be furnished to
adequately handle the rate of placing and spreading of the subbase
course.

The field density of the compacted material shall be at least 100
percent of the maximum density of laboratory specimens prepared from
samples of the subbase material delivered to the jobsite.  The
laboratory specimens shall be compacted and tested in accordance with
**\[ \]**.  The in‑place field density shall be determined in accordance
with ASTM D 1556 or ASTM D 2922.  The moisture content of the material
at the start of compaction shall not be below nor more than 2 percentage
points above the optimum moisture content.

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> **The Engineer shall specify ASTM D 698 for areas designated for
> aircraft with gross weights of 60,000 pounds (27 200 kg) or less and
> ASTM D 1557 for areas designated for aircraft with gross weights
> greater than 60,000 pounds (27 200 kg).**
>
> **Include testing frequencies per square yard or cubic yard for
> density and moisture acceptance tests.**
>
> **AASHTO T99 or T-180 (Moisture-Density) should be specified for soils
> that are expected to have more than 30% retained on the 3/4-inch
> sieve. The moisture-density relationship test procedures ASTM D 698
> and D1557 are not applicable for materials with greater than 30
> retained on the 3/4-inch sieve. A replacement procedure (ASTM D 4718)
> for the coarse material (greater than 3/4-inch) is used with ASTM
> methods but only until up to 30 percent is retained. Maximum density
> testing (ASTM D 4253) may be used but it also limits the material
> retained on the 1-1/2-inch sieve to 30 percent. The AASHTO T-99 and
> T-180 are similar to ASTM D 698 and D 1557, except they do not limit
> the replacement of the coarse material.**
>
> **Material meeting the requirements of Item P-154 may be free-draining
> which may prevent the material from retaining sufficient moisture to
> meet the moisture at compaction requirements of this paragraph. If
> this situation occurs during field operations, minimum moisture
> content should be established for placement of the material.**

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When nuclear density gages are to be used for density determination,
testing shall be in accordance with Section 120.

The course shall not be rolled when the underlying course is soft or
yielding or when the rolling causes undulation in the subbase.  When the
rolling develops irregularities that exceed 1/2 inch (12 mm) when tested
with a 16‑foot (4.8 m) straightedge, the irregular surface shall be
loosened and then refilled with the same kind of material as that used
in constructing the course and again rolled as required above.

Along places inaccessible to rollers, the subbase material shall be
tamped thoroughly with mechanical or hand tampers.

Sprinkling during rolling, if necessary, shall be in the amount and by
equipment approved by the Engineer.  Water shall not be added in such a
manner or quantity that free water will reach the underlying layer and
cause it to become soft.

**154-3.8 SURFACE TEST.**  After the course is completely compacted, the
surface shall be tested for smoothness and accuracy of grade and crown;
any portion found to lack the required smoothness or to fail in accuracy
of grade or crown shall be scarified, reshaped, recompacted, and
otherwise manipulated as the Engineer may direct until the required
smoothness and accuracy re obtained.  The finished surface shall not
vary more than 1/2 inch (12 mm) when tested with a 16‑foot (4.8 m)
straightedge applied parallel with, and at right angles to, the
centerline.

**154-3.9 THICKNESS.**  The thickness of the completed subbase course
shall be determined by depth tests or sample holes taken at intervals so
each test shall represent no more than 500 square yards (420 square
meters).  When the deficiency in thickness is more than 1/2 inch (12
mm), the Contractor shall correct such areas by scarifying, adding
satisfactory mixture, rolling, sprinkling, reshaping, and finishing in
accordance with these specifications.  The Contractor shall replace at
his/her expense the subbase material where borings are taken for test
purposes.

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> **The use of survey for thickness determination is permitted.**

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**154-3.10 PROTECTION.**  Work on subbase course shall not be conducted
during freezing temperature nor when the subgrade is wet.  When the
subbase material contains frozen material or when the underlying course
is frozen, the construction shall be stopped.

**154-3.11 MAINTENANCE.**  Following the final shaping of the material,
the subbase shall be maintained throughout its entire length by the use
of standard motor graders and rollers until, in the judgment of the
Engineer, the subbase meets all requirements and is acceptable for the
construction of the next course.

METHOD OF MEASUREMENT

**154-4.1** The yardage of subbase course to be paid for shall be the
number of cubic yards (cubic meters) of subbase course material placed,
compacted, and accepted in the completed course.  The quantity of
subbase course material shall be measured in final position based upon
depth tests or cores taken as directed by the Engineer, or at the rate
of 1 depth test for each 500 square yards (420 square meters) of subbase
course, or by means of average end areas on the complete work computed
from elevations to the nearest 0.01 foot (3 mm).  On individual depth
measurements, thicknesses more than 1/2 inch (12 mm) in excess of that
shown on the plans shall be considered as the specified thickness plus
1/2 inch (12 mm) in computing the yardage for payment.  Subbase
materials shall not be included in any other excavation quantities.

BASIS OF PAYMENT

**154-5.1**  Payment shall be made at the contract unit price per cubic
yard (cubic meter) for subbase course.  This price shall be full
compensation for furnishing all materials; for all preparation, hauling,
and placing of these materials; and for all labor, equipment, tools, and
incidentals necessary to complete the item.

Payment will be made under:

Item P‑154‑5.1 Subbase Course---per cubic yard (cubic meter)

TESTING REQUIREMENTS

ASTM C 136 Sieve Analysis of Fine and Coarse Aggregates

ASTM D 422 Particle Size Analysis of Soils

ASTM D 698 Moisture‑Density Relations of Soils and Soil‑Aggregate
Mixtures Using 5.5 lb (2.49 kg) Rammer and 12‑in (305 mm) Drop

ASTM D 1556 Density of Soil in Place by the Sand‑Cone Method

ASTM D 1557 Test for Laboratory Compaction Characteristics of Soil Using
Modified Effort

> ASTM D 2922 Density of Soil in Place by the Nuclear Density Method

ASTM D 4318 Liquid Limit, Plastic Limit, and Plasticity Index of Soils

**END OF ITEM P-154**

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