SECTION 210 — SUBGRADE
This work is preparation of the roadbed.
Form roadbed to the established subgrade elevation and compact to specified density requirements, using equipment specified in Section 108.05(c)3.a, 3.b, 3.e, or 4.
(b) Density Requirements.
Compact subgrade to not less than 100% of the determined dry-weight density. Dry-weight density for material in place in the field will be determined, in accordance with PTM No. 106, Method B. In-place density or compaction will be determined, in accordance with PTM No. 112 or PTM No. 402 where directed, for each 3,000 square yards, or less, of completed subgrade. When material is too coarse (more than 20% retained on the 3/4-inch sieve) to use these methods, compaction will be determined based on nonmovement of material under compaction equipment specified in Section 210.3(a).
At the time of compaction, maintain the subgrade material's moisture content not more than 2 percentage points above optimum moisture for that material. However, on subgrades displaying pronounced elasticity or deformation under rolling, maintain a moisture content not greater than optimum at the time of compaction or at the time of placing the overlaying construction. When the specified stability cannot be obtained, excavate material in the area to a depth that, when replaced and recompacted at a moisture content not exceeding optimum, the subgrade will have required stability.
(c) Subgrade Requirements.
In continuous lane construction, complete, progressively maintain, and protect subgrade sufficiently in advance of the succeeding operation. Prior to placement of pavement structure, promptly and satisfactorily reshape and recompact, or remove and replace, damaged or unsatisfactory areas.
Install reference grade lines with ample supports, or grade stakes, offset along each side of the subgrade, to control the elevation. Maintain reference grade lines until the surface is completed and deficiencies have been corrected.
Check subgrade for grade and slope. Test the finished surface for irregularities by using a string line stretched tautly, transversely across the subgrade area, between the reference grade lines. Measure the vertical distance from the string line to the finished grade, at various points along the string line, from one side of the surface to the other. Test for surface irregularities at longitudinal intervals of not more than 25 feet.
As an alternative or whenever the Engineer suspects an area is deficient or irregular, check the finished surface with a template and 10-foot straightedge. Test the finished surface for irregularities by using a template cut to the required cross section of the surface. Equip the template with metal or other vertical extensions attached to the top of each end to support a leveling device for checking the cross slope. The bottom of the template is to be at the elevation of the top of the subgrade. Use a 10-foot straightedge to test for longitudinal irregularities in the surface. Hold the straightedge parallel to the road centerline in contact with the surface. Move the straightedge from one side of the surface to the other. Advance along the surface in 5-foot increments.
Where subgrade is constructed using an automatic grading machine which cuts the subgrade and is controlled by a reference line or lines, the longitudinal interval for checking the surface cross section may be increased to not more than 50 feet.
Correct all surface irregularities exceeding 1/2-inch by loosening the surface and removing or adding material as required. Compact the corrected area and surrounding surface by rolling. Recheck the corrected subgrade area for grade and slope.
210.4MEASUREMENT AND PAYMENT —
Subgrade will be considered incidental to the immediate overlying pavement structure and will not be paid for separately. Subgrade, when required for shaping and finishing unpaved classes of work, will be considered incidental to those items of work.
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