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1 PART 3: EXECUTION <br /> 2 <br /> 3 3.01 TRENCH EXCAVATION <br /> a <br /> s A. Trenching Guidelines: Excavate the trench to the approximate level of the top of the utility <br /> 6 line to be installed, using adequate trench width and side slopes to safely accommodate <br /> 7 worker access. Continue excavating for the utility line, to a width not greater than is shown <br /> 8 on the appropriate trench detail. <br /> s <br /> 10 1. Rocky Trench Bottom: Where ledge rock, hard pan, boulders, or sharp-edged <br /> 11 materials are encountered, over-excavate a minimum depth of 6 inches below the <br /> 12 bottom of the utility exterior wall to permit adequate bedding preparation. The installed <br /> 13 utility shall have at least 6 inches of clearance from any rock protrusion. <br /> 14 <br /> 15 2. Unstable Trench Bottom: Secure approval of depth of over excavation and stabilization <br /> 16 method. For wet trench construction, use approved method of dewatering through <br /> 17 diversion, damming and pumping, well points, or underdrain systems. Dispose of <br /> 18 removed fluidized materials as approved. Use BD-3 material to build a suitable <br /> 19 foundation to within 4 inches of the pipe. Compact layers to 95 percent of maximum <br /> 20 density in not greater than 6-inch layers. Do not proceed with utility installation until <br /> 21 wet trench and unstable conditions are under control. <br /> 22 <br /> 23 3.02 SHORING AND SHEETING <br /> 24 <br /> 25 A. Construct and maintain all shoring, sheeting, and slope layback necessary to protect the <br /> 26 excavation, as needed for the safety of the employees and as required by to <br /> State <br /> 27 and Federal laws. <br /> 28 <br /> 29 B. For trenches over 5 feet deep, provide suitable barricades for worker protection. When <br /> 30 work area is left open and unattended by Contractor, provide suitable barricades for public <br /> 31 safety, regardless of trench depth. <br /> 32 <br /> 33 C. For trenches over 4 feet deep, provide suitable exit means in accordance with applicable <br /> 34 provisions of OSHA. <br /> 35 <br /> 36 D. Do not remove timber or sheeting if it is in a compacted zone. Instead, trim it off at a safe <br /> 37 level above that zone. <br /> 38 <br /> 39 E. As directed, remove all other sheeting and shoring when safe to do so. <br /> ao <br /> 41 3.03 BACKFILLING <br /> 42 <br /> 43 A. Compaction: Use vibratory compactors for sands and gravels (noncohesive soils).-graineUse <br /> 44 mechanical tampers for sand and gravel containinga significant <br /> 45 material, such as silt and clay (cohesive soils). Hand tamp around pipe portion <br /> or cable to protect <br /> 46 the lines until adequate cushion is attained. Jetting backfill in non-traffic areas will be <br /> 47 allowed provided that the Contractor can demonstrate his proposed method will consistently <br /> 48 achieve the specified compaction. Jetting operation shall not disturb the pipe or any <br /> 49 bedding or select backfill within 12 inches of the pipe. <br /> 50 <br /> UTILITY TRENCHING & BACKFILUNG , <br /> 050594 02221-4 <br /> r <br /> r <br />