208SPECIAL ROLLING

208.1DESCRIPTION—This work is the special rolling of existing embankments; structure foundations on

soil; existing subgrades; and the excavation and backfilling of the unstable areas, as indicated or as directed.

208.2MATERIAL—

208.3CONSTRUCTION—Perform special rolling in the presence of the Representative who will approve

or disapprove the stability of the embankment and recommend corrective measures.

Use a 2-axle pneumatic roller that will transmit the load through a minimum of four wheels on each axle. The wheels must be equally spaced over the roller width, be equally inflated, and have independent suspension, so that the wheels will carry approximately equal loads when operated over an uneven surface. Use a pneumatic roller with tires capable of operating at inflation pressures ranging from 100 pounds per square inch to 105 pounds per square inch, the minimum wheel path overlap is 0.5 feet. All tires are to be smooth or have a low void ratio tread. The pneumatic roller should be no more than 10 feet wide overall.

and cohesive materials. The sheepsfoot or pad roller is to have a minimum foot or pad contact pressure of 160 pounds per square inch.

with a minimum dynamic force at the drum of 50,000 pounds.

on newly constructed subgrades. Perform special rolling on embankment foundations, existing embankments where the grade is being raised, and structure foundations with spread footings bearing on soil.

• Before special rolling, compact the area as specified in Section 206.3(b). For areas of subgrade construction, prepare as specified in Section 210.

• For soils as specified in Section 206.2(a).1. a, use either a sheepsfoot, pad foot, or pneumatic tired roller. Do not use vibratory compaction, run all equipment in static mode. Operate roller at a maximum speed of 2 miles per hour . Observe that the sheepsfoot or pad foot roller "walks -out" of the soil. Alternatively, run a pneumatic roller and observe behavior of the roller and material.

• For granular materials as specified in Section 206.2(a)1.b and Section 206.2(a)1.c, compact the area as specified in Section 206.3(b)1.b or Section 206.3(b)1.c . Operate the smooth steel drum vibratory

roller at a speed not exceeding 2 miles per hour. Do not use a smooth drum roller with vibratory drum on fine grained soils such as silt and fine sands.

• Compact material to 97% of maximum dry density for embankment foundations or for existing embankments greater than 3 feet below the proposed subgrade elevation. Compact material to 100% of maximum dry density for structure foundations, subgrades, or for material within 3 feet of proposed subgrade elevation. Compact material at a moisture content between minus 3% of optimum moisture content and optimum moisture content. Material that is above the optimum moisture content, must be dried by disking, scarifying, or other means, until the material meets the moisture content requirements before compaction.

• When moisture-density test data is not available, compact with the proposed equipment using a test strip approach. After each pass of the compaction equipment, check the in-place moisture and density at several pre-determined random locations according to AASHTO T 191 or AASHTO T 310. When the measured moisture density does not increase by more than 1% over three consecutive passes of the compaction equipment, and the material appears stable, then proceed to special rolling. If the material cannot be compacted to a stable mass, the material is too wet and must be dried and recompacted, as above, to a stable mass before proceeding to special rolling.

• When special rolling using a loaded triaxle dump truck (72,000 pounds, gross vehicle weight), perform special rolling only in the presence of the Representative who will assess, and approve or disapprove the stability of the area being investigated. Run the loaded triaxle dump truck in a systematic manner to investigate the stability of the entire area indicated, or as directed. Additional passes of special rolling equipment may be ordered by the Representative to assess the soils. The Representative may waive special rolling requirements in wet or unstable areas if other stabilization or treatment measures are specified or required.

• Do not substitute special rolling for compaction procedures. Protect structures such as bridges, box and pipe culverts, from damage by special rolling equipment. Do not perform special rolling within 10 feet of bridge abutments or approach slabs.

stabilize the subgrade by providing compaction or by undercutting/excavating and replacing the unsuitable subgrade material. Unsatisfactory stability due to special rolling is defined as one of the following:

• For existing subgrade, subgrade in cut, spread footing on soil, when the permanent deflection or rutting is greater than 1/2 inch.

• For embankment foundations, including existing embankment when the grade is being raised, if the permanent deflection or rutting is greater than 1 inch of permanent deflection.

of excavation is as directed and as follows:

than 8H:1V. Compact the bottom of the undercut.

1.a. 1 Foot Depth Subgrade Undercut. For subgrade areas with greater than 0.5 inch and less than or equal to 3 inches of permanent deflection when performing Special Rolling, e xcavate the failed subgrade area to a depth of 1 foot as directed. Place Geotextile Class 4, Type C, as directed at the bottom of the undercut as specified in Section 212.3(e). If directed, drain the undercut by excavating a drainage path and backfilling it with No. 57 aggregate. Place Selected Borrow Excavation or other material as specified in Section 205. Compact aggregate as specified in Section 206.3 and Section 210.3. A minimum of 8 inches of approved material is to be in place on the geotextile before compaction.

2.a. 3 Foot Maximum Depth Subgrade Undercut. For subgrade areas with greater than 3 inches of permanent deflection when performing Special Rolling, excavate the failed subgrade area to a maximum

depth of 3 feet as directed. Place Geotextile, Class 4, Type C at the bottom of undercut as specified in Section 212.3(e). If directed, drain the undercut by excavating a drainage path and backfilling it with No. 57 aggregate. Place Selected Borrow Excavation or other material as specified in Section 205. Compact aggregate as specified in Section 206.3 and Section 210.3. A minimum of 8 inches of approved material is to be in place on the geotextile before compaction. Place a layer of Geotextile, Class 4, Type A as specified in Section 212.3(d) on Selected Borrow Excavation used to backfill the undercut before placing subbase on the undercut area. A minimum of 6 inches of subbase is to be placed on the geotextile before compaction. Protect existing underground utilities during undercut operations.

208.4MEASUREMENT AND PAYMENT—

Special rolling is paid by the hour, measured to the nearest 0.25 hour, in which special rolling is being performed in the presence of the Representative. Payment will not be made to correct damage caused by the Contractor to the subgrade. No measurement and payment will be made for idle equipment time for testing of materials, repairs or servicing equipment, loading or unloading ballast, increasing or decreasing tire pressure, inclement weather, or for any other similar reason under the control of the Contractor.

average end area method. All labor, materials and equipment required to excavate, drain, and backfill areas are included in the cubic yard item.

For the type indicated or specified.