2110.01 DESCRIPTION.
Soil aggregate subbase shall consist of soil from the subgrade combined with mineral aggregate present on the road surface, with or without additional aggregate, spread, shaped, and compacted in accordance with the contract documents.

2110.02 MATERIALS.
Granular material used shall consist of any granular material that may be present on the roadbed plus the specified quantity of material meeting the requirements of Section 4120.

2110.03 SOIL AGGREGATE SUBBASE EQUIPMENT.
Equipment used shall meet requirements of Section 2001 and the following:

A. Weighing Equipment.
Article 2001.07 shall apply.

B. Compaction Equipment.
Article 2001.05 shall apply except that other types of equipment may be used provided it is demonstrated that they will consistently produce the specified density. The equipment shall be of a design that its operation will not distort the subgrade.

C. Equipment for Applying Water.
Article 2001.09 shall apply.

D. Field Laboratory.
Section 2520 shall apply.

2110.04 ROADBED CORRECTION.
That portion of the roadbed to be used for soil aggregate subbase shall be corrected in accordance with Article 2111.04.

2110.05 CONSTRUCTION.
Soil aggregate subbase shall be constructed to the width and thickness shown in the contract documents. Any loose granular material present on the roadbed and previously stored on the shoulder area during roadbed correction shall be spread uniformly over the area to be occupied by the subbase.

The Contractor may be required by the contract documents to furnish granular material for subbase construction in addition to that present on the existing roadbed. This additional material shall be uniformly distributed over the area to be occupied by the subbase at the rates specified.

The roadbed shall then be bladed or scarified to such depth as is necessary to produce a smooth subgrade of the cross section shown in the contract documents and to provide the quantity of material which, when combined with the granular material to be added, will produce a compacted subbase of the thickness designated.

The methods and sequence of operations shall be adapted to the width of roadbed and quantity of granular material to be added to insure the following results:

A. The materials from the road surface and granular material added shall be mixed to such a degree that there are no seams or streaks of separate material in evidence from visual inspection, and shall be pulverized so that there are no soil particles larger than 2 inches (50 mm) in greatest dimension.

B. The moisture content of the soil aggregate mixture will be approved on the basis of visual inspection. It shall be uniformly wetted or dried, so that at the time it is spread and compacted, it shall contain the amount of water necessary to obtain the required density, together with stability, with the field compaction process. This moisture content shall be maintained in the mixture until compaction is completed. The wetted material shall be placed in windrows prior to spreading for compaction, and distortions of the subgrade greater than 1 inch (25 mm) above or below the intended plane of the bottom of the subbase shall be corrected by smoothing and rolling.

C. At railroad crossings, junctions with existing pavement, bridges, and similar structures, the subgrade shall be excavated to permit the full thickness of subbase, base, and surface courses to be constructed to the proper elevation. For a distance of 50 feet (15 m) from railroad crossings, bridges, and existing intersecting pavements, the soil aggregate subbase shall be omitted. In these areas, the specified base shall be thickened sufficiently to replace the omitted subbase.

D. The surface on which the subbase is to be constructed shall be sprinkled with water as necessary to assure a moist condition to a depth of at least 1/2 inch (15 mm).

The prepared subbase material shall then be spread and shaped to assure conformance with the cross section shown in the contract documents, after compaction. The subbase shall be compacted at the moisture content specified in Paragraph B to a density not less than 95% of maximum density as determined by Iowa DOT Materials Laboratory Test Method 103. During compaction operations, such additional shaping shall be performed as may be necessary. The profile and cross-section shall meet requirements of Article 2111.06.

2110.06 MAINTENANCE OF COMPLETED SUBBASE.
Article 2111.07 shall apply.

2110.07 METHOD OF MEASUREMENT.

A. Construction of Soil Aggregate Subbase.
The quantity of Soil Aggregate Subbase, in miles (kilometers), will be the quantity shown on the contract documents. The quantity of Soil Aggregate Subbase will be determined along the center line of the subbase, including approaches to railroad crossings, bridges, and similar structures. At intersections, the length of subbase will not include that portion of centerline which overlaps previously determined pavement, base course, or subbase.

B. Granular Material.
Granular material for soil aggregate subbase will be measured in tons (megagrams) as computed by the Engineer from the weights (mass) of material delivered. No deduction will be made for moisture naturally occurring in the material.

2110.08 BASIS OF PAYMENT.

A. Construction of Soil Aggregate Subbase.
The Contractor will be paid the contract unit price for Soil Aggregate Subbase per mile (kilometer). This payment shall be full compensation for roadbed correction, for furnishing and applying water, and for doing all work necessary for completion of the soil aggregate subbase in compliance with the contract documents except for furnishing and hauling granular material.

B. Granular Material.
For the number of tons (megagrams) of granular material for soil aggregate subbase furnished by the Contractor and incorporated in the work, the Contractor will be paid the contract unit price per ton (megagram).

Excavation or filling for roadbed correction in excess of 3 inches (75 mm) at locations other than structures or existing pavement will be paid for according to Article 2102.14, or if no contract unit price is provided, as extra work.