ITEM 204 SUBGRADE Compaction and proof rolling
204.01
Description
204.02
Materials
204.03
Compaction of the Subgrade
204.04 Unstable
Subgrade
204.05 Rock,
Shale, or Coal Subgrade
204.06 Proof
Rolling
204.07
Spreading and Placing of Materials
204.08 Method
of Measurement
204.09 Basis of
Payment
204.01 Description. This work consists of
preparing suitable subgrade material by drying, compacting, proof rolling, and
grading. This work also consists of removing unsuitable subgrade material
and constructing new embankment to the limits shown on the plans.
The
contract documents provide the anticipated amount of excavation for unsuitable
subgrade material which includes unsuitable soil, rock, shale, and coal in the
subgrade, and for unstable subgrade material.
Use
removed or excavated materials in the Work when the material conforms to the
specifications; if not, then recycle or dispose of the material according to 105.16 and 105.17.
204.02 Materials. Furnish suitable material
conforming to 203.02.R, 203.03, and 703.16,
except use soils in the top 12 inches (300 mm) of the subgrade that have a
maximum dry density of at least 100 pounds per cubic foot (1600 kg/m³).
Furnish
material that conforms to 703.16.B or 703.16.C when Granular Embankment is
specified. Furnish material that conforms to 703.16.C when Granular Material, Type ___
is specified, except do not use RPCC, EAF slag, or BOF slag.
Do
not use Granular Material Type D, E, or F in the location where underdrains are to be constructed.
Furnish
geotextile fabric that conforms to 712.09,
Type D
204.03 Compaction of the Subgrade. Compact subgrade materials that have a maximum dry density of 100
to 105 pounds per cubic foot (1600 to 1680 kg/m³) to not less than 102 percent
of maximum dry density. Compact all other subgrade materials to
not less than 100 percent of maximum dry density. Determine the maximum
dry density using AASHTO T 99, AASHTO T 272, or test section method described in Supplement
1015, according to the Engineer. The Department may check for
compaction before or after the fine grading operation.
If needed for
compaction acceptance, use the test section method as follows:
A. Use a minimum of eight passes with a
steel drum roller having a minimum effective weight of 10 tons (9 metric tons).
B. Use 98 percent of the
test section maximum dry density for acceptance of the production subgrade
compaction.
C. Use at least the same number of passes
and compactive effort used to construct the test section for the production
subgrade compaction.
D. Construct a new test section when the
subgrade material, supporting foundation or embankment material changes.
E. Reduce the moisture content if the
material becomes unstable. The Engineer may reduce the minimum number of
passes if the passes are detrimental to compaction.
Use the moisture
controls specified in 203.07.A.
Compact the
subgrade under pavements to a depth of 12 inches (300 mm) below the
subgrade surface and 18 inches (450 mm) beyond the edge of the surface of
the pavement, paved shoulders, or paved medians. Compact all subgrades
under paved driveways, paved mailbox turnouts, curbs and gutters to a depth of
12 inches (300 mm) below the subgrade surface.
Maintain and
drain the subgrade according to 203.04.A.
204.04 Unstable Subgrade. If satisfactory
subgrade stability cannot be obtained by moisture control and compaction
according to 204.03, the Engineer will direct
the Contractor to remove the unstable material and to construct the replacement
material to the finished grade within the tolerances specified in 203.08.
Conduct
the removal and replacement operations to allow the Engineer to measure the
cross-sections before placing the replacement material.
Remove
the unstable subgrade material to the depth determined by the Engineer or
specified in the Contract Documents. Replace with suitable material
according to 204.07.
204.05 Rock, Shale, or Coal Subgrade. If an
aggregate base is not a part of the pavement design, excavate the subgrade 2
feet (0.6 m) below the final subgrade elevation where rock, shale, or coal is
encountered. If an aggregate base is part of the pavement design, reduce
the above 2-foot (0.6 m) excavation depth by the thickness of the aggregate
base or bases. Maintain a total excavation depth of 2 feet (0.6 m) below
the bottom of the asphalt or concrete pavement.
Excavate
for a width of 1 foot (0.3 m) beyond the shoulders. Replace with suitable
material according to 204.07.
204.06 Proof Rolling. Test the stability and
uniformity of the subgrade compaction by proof rolling.
A. Use a proof roller conforming to the
following:
1.
Four heavy pneumatic tire wheels mounted on a rigid steel frame.
2.
Wheels evenly spaced in one line across the width of the roller.
3.
Wheels arranged so that all wheels carry approximately equal loads when
operated over an uneven surface.
4.
A maximum center-to-center spacing between adjacent wheels not exceeding 32
inches (0.8 m).
5.
A body for ballast loading capable of varying the gross load from 25 to 50 tons
(23 to 45 metric tons).
6.
Tires capable of operating at inflation pressures ranging from 90 to 120 pounds
per square inch (620 to 830 kPa). Provide a
tire pressure gage for measurement before use.
7.
Tires filled with liquid from 90 to 95 percent by volume.
Provide ballast that
consist of blocks of known weight, sand bags with a weight of 100 pounds (45
kg), bags of other material of known weight, or other suitable material such
that the total ballast weight is readily determinable at all times.
Provide sufficient ballast to load equipment to a maximum gross weight of 50
tons (45 metric tons).
Furnish the Engineer
information verifying that the weights and tire pressures can be met.
B. After compacting
the subgrade according to 204.03 and before
placing overlying course, proof roll designated subgrade areas. If proof
rolling is performed after the underdrains are
installed, do not use the proof roller within 1 1/2 feet (450 mm) of the underdrains.
Ensure that the
subgrade moisture content at the time of proof rolling is within 2 percent of
the moisture used for acceptance in 204.03.
Adjust the load and
tire inflation pressure as directed by the Engineer or according to the
following:
1.
For soils classified as A-3, A-4, A-6, or A-7-6, use a 35-ton (32 metric tons)
roller with a tire pressure of 120 pounds per square inch (820 kPa).
2.
For granular soils, and soil, rock, and granular mixtures,
use a 50-ton (46 metric tons) roller with a tire pressure of 120 pounds
per square inch (830 kPa).
3.
When proof rolling areas where unsuitable or unstable subgrade materials have
already been excavated and replaced with granular material, use the weight and
tire pressure appropriate for the original subgrade material type.
Measure the tire
pressure in the presence of the Engineer. Operate equipment at a speed
between 2 1/2 and 5 miles per hour (4 and 8 km/hr).
Adjust the speed to allow the Engineer to measure the deflections, ruts, or
elasticity. Make only one trip of the proof roller over any area. Offset
trips to completely cover the subgrade area.
Where proof rolling
indicates areas of unstable subgrade, the Engineer will investigate for the
source of the problem. The Contractor is responsible for all problems
found in the materials constructed under the Contract Documents. Correct
all deficiencies found. Correct the subgrade to a uniform and
satisfactory stability as directed by the Engineer.
After proof rolling,
check the subgrade for conformance to the plans, and correct all surface
irregularities. Shape the subgrade within the tolerances specified in 203.08.
204.07 Spreading and Placing of Materials. Place
materials, conforming to 204.02, in 8-inch (200
mm) loose lifts. The Engineer may increase the lift thickness depending
on the stability of the bottom of the excavation. The Engineer may
increase the lift thickness up to 24 inches (600 mm) to obtain stability at the
top of the lift. Doze, track, or manipulate the material to maximize the
density and stability. Once stability is achieved, compact according to 204.03.
When
specified, place geotextile fabric at the bottom of the cut or at locations
designated in the Contract Documents. Place the geotextile fabric smooth
and free of tension or wrinkles. Fold or cut the geotextile fabric to
conform to curves. Overlap a minimum of 18 inches (450 mm) at the ends
and sides. Hold the geotextile fabric in place with pins or staples.
End dump the suitable
material on the geotextile fabric. Do not operate the equipment directly
on the geotextile fabric. Unless stated otherwise, spread the end dumped
material and maintain a minimum lift thickness of 12 inches (300 mm).
When
granular material Type E is specified or allowed, use a geotextile fabric on the
top, bottom and around the Type E granular material to prevent piping of
material into the Type E granular material. The Engineer may use granular
material Type E when excess water is at the bottom of the cut.
204.08 Method of Measurement. The Department
will measure Subgrade Compaction by the number of square yards (square meters)
computed from the profile grade and typical sections and actually
compacted. The Department will measure 18 inches (450 mm) beyond the edge
of the pavement surface, paved shoulders, and paved medians. The
Department will measure the surface area of the paved driveways, paved mailbox
turnouts, curb, and gutter.
The
Department will measure Proof Rolling by the number of hours accepted.
The Department will not measure idle time for repairs, servicing, loading and
unloading ballast, adjusting tire pressure, bad weather, wet subgrade, usage at
times and at locations other than Department directed, and stand-by time to be
available when next needed or other cause for stand-by time.
The
Department will measure Excavation of Subgrade; Embankment; Granular
Embankment; and Granular Material, Type ___ according to 203.09. All excavation is unclassified.
The
Department will measure Geotextile Fabric by the number square yards (square
meters) of surface area of geotextile fabric placed. The Department will
not measure the specified lap length.
204.09 Basis of Payment. The
Department will pay according to 109.05 for
changes or extra work that increases the haul distance more than a 1/2 mile (1
km) to the work detailed in the Contract Documents. The Department will
pay for additional quantities that increase the haul distance 1/2 mile (1 km)
or less at the unit bid price.
If
unstable subgrade results from inadequate surface drainage or lack of
maintenance, as required by 203.04.A, the
Department will not pay for replacing the unstable subgrade and disposing of
the removed material.
For
problems identified in 204.06 that are the
result of soils or conditions at lower elevations than the Contract work, the
Department will pay for the corrections.
The
Department will pay for the subgrade compaction in areas requiring excavation
and replacement in 204.04, 204.05, and 204.07.
The Department will not pay for subgrade compaction in areas stabilized under
Item 206.
The
Department will pay for accepted quantities at the contract prices as follows:
Item
Unit
Description
204
Square
Yard
Subgrade Compaction
(Square Meter)
204
Hour
Proof Rolling
204
Cubic
Yard
Excavation of Subgrade
(Cubic Meter)
204
Cubic
Yard
Embankment
(Cubic Meter)
204
Cubic
Yard
Granular Embankment
(Cubic Meter)
204
Cubic
Yard
Granular Material Type ___
(Cubic Meter)
204
Square
Yard
Geotextile Fabric
(Square Meter)