An underground utility trench profile features a pipe bedded in well-graded sand, gravel, or Class 2 aggregate base conforming to Caltrans specifications. The pipe maintains a minimum of six inches of clearance on each side and above the outer diameter, with a bedding thickness underneath of four inches or one-quarter of the pipe outside diameter. Trench backfill general fill is placed in lifts not exceeding eight inches in uncompacted thickness and compacted to at least ninety percent relative compaction by mechanical means only, with jetting explicitly prohibited.
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