Trench cross-section containing bedding, pipe zone backfill, and trench dimensions for underground utility installations. Type I rigid non-pressure pipe rests on an undisturbed shaped surface with a half-pipe outer diameter clearance, while Type II flexible non-pressure pipe is bedded on a minimum of six inches of sand. The pipe zone extends twelve inches minimum above the top of the pipe and twelve inches minimum on each side of the pipe outer diameter. Maximum trench width at the top of the pipe is governed by the pipe inside diameter, requiring outer diameter plus twenty-four inches for pipes less than thirty-three inches, and outer diameter plus thirty inches for pipes greater than thirty-three inches. Backfill in the pipe zone is placed in horizontal eight-inch deep loose layers and compacted to ninety-six percent ASTM D-1557 density.
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