(A) The surface of the subgrade when excavated, rolled and compacted shall conform to the designed profile and cross sections so that it is not higher than the designed elevations and at no point lower than 0.05 feet below design elevations.
(B) The subgrade shall be so constructed as to have uniform stability for a width at least equal to that of the proposed pavement, plus one foot on each side, or full width between previously placed curb and gutter sections.
(C) Stones over four inches in size shall be removed from the loosened portion of the subgrade and disposed of as directed by the engineer.
(D) Depressions that develop during rolling shall be filled with suitable material, and rolling shall continue until the subgrade is uniformly firm, properly shaped and substantially true to grade and cross-section.
(E) Material, other than sand, which will not compact readily under the roller shall be removed and replaced with material which will compact readily, and that portion of the subgrade shall be rolled again.
(F) Rolling of the subgrade shall extend for at least 12 inches outside each edge of the proposed bottom of the pavement. Piles or ridges of earth or material that seriously interferes with the operation of finishing the pavement shall be removed from the shoulders.
(G) During the process of constructing the subgrade, the soil shall be maintained in a condition, sufficiently moist as to facilitate compaction and produce a firm, compact surface. Such sprinkling or wetting of the finished subgrade will be required, as may be necessary to ensure a reasonable moisture content.
(H) Perform proof rolling with a truck loaded to the maximum single legal axle gross weight of 20,000 pounds or the maximum tandem axle gross weight of 34,000 pounds. Operate trucks at less than ten mph. Make multiple passes for every lane. The subgrade will be considered to be unstable if, under the operation of the loaded truck, the surface shows yielding (soil wave in front of the loaded tires) or rutting of more than two inches, measured from the top to the bottom of the rut at the outside edges. The expense of such load testing shall be the contractor’s expense.
(I) (1) Unstable subgrade conditions shall be noted by the engineer and repaired to the extent required by the engineer.
(2) Such repairs shall be made as follows.
(a) The unsuitable earth materials shall be removed to the depth needed.
(b) The bottom of the excavation shall be compacted. If the bottom of this excavation consists of earthen material that will not compact to the proper density, the earthen materials shall be stabilized via cement or fly ash stabilization, replacement of unstabilized earth with IDOT gradation 13 or other stabilizing method approved by the engineer.
(c) The engineer may decide, in lieu of the above, to specify strengthening of the pavement structure in unstable areas; this work to be paid for as an extra work item.
(d) When the bottom of the excavation is suitably stable to support layers of compacted earth, the excavation will be filled with suitable backfill materials and compacted in no more than six inch lifts to 95% optimum density as shown by the Standard Proctor Test. Backfill materials may be either IDOT gradation 30 crushed stone or suitable earth backfill approved by the engineer.
(e) The source of earth backfill shall be approved by the engineer prior to the use of the material.
(f) After the subgrade has been repaired, it shall be shaped to final cross-section and elevation. Visual checks shall then be made by the engineer to determine any soft or spongy spots. Any such areas so detected shall again be repaired, provided they are within the top six inches of the subgrade.
(g) The subgrade shall be kept shaped and drained at all times to prevent the development of soft or spongy areas. In no case shall any improvement be placed on muddy subgrade or one that has not been checked and approved. Delays resulting in the contractor’s failure to adequately protect the subgrade shall be recorded. Subgrade repairs resulting from the contractor’s negligence shall be the contractor’s expense.
(h) Accurate records on subgrade repairs, signed by the inspector, shall be kept. The inspector’s signature upon such daily records shall be the Inspector’s approval of daily effort expended, quantities of material compacted and quality of workmanship. These records shall be used as a basis of payment.
(i) Any subgrade repair made more than once in the same spot shall not be paid for if such a condition resulted through negligence or poor workmanship by the contractor.