SECTION 350 — SUBBASE


350.1 DESCRIPTION — This work is construction of compacted aggregate on a prepared subgrade area and includes the preparation of subgrade, as specified in Section 210.


350.2 MATERIAL —

(a) Aggregates. Type C or better, No. 2A and No. OGS, Section 703.2 as specified.
Acceptance testing of aggregates will be performed at the source. Obtain verification samples at the job site, under the direction and supervision of the Inspector, after the subbase material has been spread in place, but before it is compacted.


350.3 CONSTRUCTION —

(a) Equipment.

1. Spreaders. Section 320.3(a)3.

2. Compaction Equipment. Sections 108.05(c)3.a, 3.b, 3.e

(b) General. Prepare the subgrade prior to placing subbase.
Do not place subbase material on soft, muddy, or frozen areas. Before placing subbase, satisfactorily correct irregularities or soft areas in the prepared area.
Correct unsatisfactory subbase conditions developing ahead of the base and paving operations by scarifying, reshaping, and recompacting, or by replacement, if directed.

(c) Mixing. Mix materials and water by acceptable methods. Blend materials, if permitted, and mix prior to delivery to the work site. Use material uniformly graded and containing enough moisture to prevent segregation during stockpiling, hauling, and placing, and to minimize the need for adding water during compaction. Maintain No. OGS material in a well moistened condition during the period from before placement up to compaction.

(d) Placement. Control the elevation and depth of the subbase in accordance with Section 210.3(c); however, where subbase is trimmed using an automatic grading machine, templates will not be required. Deposit the material on the prepared area by means of spreaders, in a manner which will not cause segregation. In areas where the use of mechanical spreaders is impractical, spread, using an acceptable method. For rigid pavement and shoulders, place a layer of No. 2A to a minimum compacted depth of 3 inches and each layer of No. OGS, if indicated, to a minimum compacted depth of 4 inches, and at a position in the pavement structure as indicated. Construct subbase in courses not over 8 inches in compacted depth; however, when granulated slag is used, construct in courses not over 4 inches in compacted depth. When using granulated slag, a maximum compacted layer of 6 inches may be placed, if permitted, when the required compaction density can be obtained for the full depth of each layer. Avoid using open-graded subbase as a haul road and confine the open-graded subbase material by construction of berms prior to placing.
Place subbase prior to paving as shown on the standard drawings. If constructed in partial width, finish the remainder to its full width after the completed edge of the subbase is neatly trimmed.
For continuous construction, complete and progressively maintain the subbase for not less than 1,500 linear feet in advance of the succeeding operation. In areas inaccessible to mechanical spreaders and in special areas, deposit the subbase material on the prepared area, if permitted. Spread, in a manner not causing segregation, to attain the full uniform depth of the layer being placed. Use acceptable equipment and methods.

(e) Compaction and Density. Compact the uniformly spread material to not less than 100% of the maximum dry-weight density, which will be determined in accordance with PTM No. 106, Method B. The in-place density will be determined in accordance with PTM No. 112, or PTM No. 402 where directed, for each 3,000 square yards, or less, of each layer of completed subbase, for No. 2A material. When the subbase material is too coarse (more than 20% retained on the 3/4-inch sieve) to use these methods or when No. OGS material is used, compaction will be determined based on nonmovement of the material under the compaction equipment. Proceed with compaction gradually from sides to center, with each succeeding pass uniformly overlapping the previous pass. Continue until the entire area is satisfactorily shaped and compacted.
If subbase material does not contain sufficient moisture after placement, add water to obtain proper compaction. Otherwise, remix, reconstruct, or replace the material, as directed.

(f) Surface Tolerance. Section 210.3(c)

(g) Test for Depth. Carefully dig one test hole to the full depth of the completed subbase, where directed, for each 3,000 square yards or less of completed subbase.
The Engineer will measure the depth of the finished subbase.
Where subbase is 1/2-inch or more deficient from the depth indicated, scarify to a 3-inch depth, blend with additional material, recompact, or otherwise correct, as directed. Additional test holes may be required, if directed, to determine the limits of defective areas.
After the depth has been measured, backfill test holes with acceptable material and compact.

(h) Maintenance and Traffic. Section 320.3(j) and as follows:
If completed subbase is subjected to hauling or exposed to weather in excess of 60 calendar days, retest for surface irregularities and depth and correct deficiencies as specified in Section 350.3(f) and (g).

Keep all construction equipment and traffic off of compacted No. OGS unless specifically authorized by the Engineer.


350.4 MEASUREMENT AND PAYMENT — Square Yard

Subbase will not be paid for complete in place until the base course or pavement is constructed. However, payment may be made to 75% of the quantity of the subbase on current estimates, in advance of the succeeding operations, provided the subbase has been satisfactorily completed and maintained, pending placement of the base course or pavement.

No Supplement

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