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3.02 REFILL <br />A. If the material at the level of trench bottom consists of fine sand or sand and silt <br />which may work into the drain rock prohibiting effective drainage, the sub -grade <br />material shall be removed to the extent directed and the excavation refilled with <br />coarse sand, or a mixture graded from coarse sand to fine pea - stone, to form a <br />filter layer preserving the voids in the gravel bed of the pipe. The composition and <br />gradation of gravel shall be approved by the Engineer prior to placement. Gravel <br />shall be placed in 6 inch layers thoroughly compacted to 90 percent of maximum <br />standard proctor density. If directed by the Engineer, drain rock shall be used for <br />refill of excavation below grade. <br />END OF SECTION <br />05/08 02223 -2 05 -4893 <br />