A typical storm sewer trench section incorporates specific bedding and backfill configurations for pipe diameters under and over 48 inches. The trench width is designated as 2 feet plus the inner diameter, bounded by support as required and edge of trench lines. Pipe bedding consists of 3/4-inch crushed stone extending to the edge of the trench, with a minimum depth of 4 inches up to 1 foot in rock, and a 1-foot minimum for PVC pipe. Suitable approved backfill or Type GW, GP, SW, and SP soil per the Unified Soil Classification System is compacted to 95 percent maximum dry density in 8-inch lifts per ASTM D-1557. A 3/4-inch crushed stone zone extends above the pipe zone up to 1 foot minimum.
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