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ENGEO <br /> INCORPORATED <br /> <br /> <br />5150.100.101 <br />May 2, 2008 Page 15 <br />Compact the pavement Caltrans Class 2 Aggregate Base section to at least 95 percent relative <br />compaction (ASTM D1557). Moisture condition aggregate base to or slightly above the <br />optimum moisture content prior to compaction. <br /> <br />6.6.2 Underground Utility Backfill <br /> <br />6.6.2.1 General <br /> <br />The contractor is responsible for conducting all trenching and shoring in accordance with <br />CALOSHA requirements. Project consultants involved in utility design should specify pipe <br />bedding materials. <br /> <br />6.6.2.2 Structural Areas <br /> <br />Place and compact trench backfill as follows: <br /> <br />1. Trench backfill should have a maximum particle size of 8 inches; <br /> <br />2. Moisture condition trench backfill to or slightly above the optimum moisture content. <br />Moisture condition backfill outside the trench; <br /> <br />3. Place fill in loose lifts not exceeding 12 inches; <br /> <br />4. Compact fill to a minimum of 90 percent relative compaction (ASTM D1557). <br /> <br />Where utility trenches cross perimeter building foundations, backfill with native clay soil for <br />pipe bedding and backfill for a distance of 2 feet on each side of the foundation. This will help <br />prevent the normally granular bedding materials from acting as a conduit for water to enter <br />beneath the building. As an alternative, a sand cement slurry (minimum 28-day compressive <br />strength of 500 psi) may be used in place of native clay soil. <br />