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the pipe will rest firmly on undisturbed soil. The 1/4 portion of the pipe trench shall be excavated only a few feet in advance of pipe laying, by men especially skilled in this type of work. For excavation of manholes and other accessories it shall be sufficient to leave at least 12 inches in the clear between their outer surfaces and the banks. Except at locations where excava­tion of rock from the bottoms of trenches is required, care shall be taken not to excavate below the depths indicated on the plans. Where rock excavation, as defined in paragraph b, below, is re­quired, the rock shall be excavated to an overdepth of 6" unless otherwise instructed by City Inspector, The overdepth rock excavation and all excess trench excavation shall be backfilled with loose, moist earth, thoroughly tamped. Whenever wet or otherwise unstable soil incapable of properly supporting Pipe is encountered in trench bottom, backfill should conform with typical sections shown on City of Las Vegas Drwg. SS-D1-1047, as directed by City Inspector. Any excess excavation below levels indicated shall be filled with sand, gravel, or concrete at the expense of the contractor as directed by City Inspector. A. Trench Excavation (Common) French excavation shall comprise the satisfactory removal and disposition of all materials not classified a.s rock excavation, and shall include clay, silt, sand, gravel, hardpan, loose shale and other loose stone in masses, and boulders measur­ing less than 1/3 cubic yards in volume. B. Rock Excavation Rock excavation shall comprise and include the satis­factory removal of the following! (1) all boulders measuring - 2