Trench Type Type 5 Type 4 Type 3 Pipe bedded in compacted granular material to the centerline of the pipe, 4 inches minimum under the pipe. Compacted granular or select material to top of pipe. (Approximately 90 percent Standard Proctor, AASHTO T-99) Pipe bedded in sand, gravel, or crushed stone to a depth of 1/8 pipe diameter, 4 inch minimum. Backfill compacted to top of pipe. (Approximately 80 percent Standard Proctor, AASHTO T-99) Pipe bedded in 4 inches minimum loose soil. Backfill lightly consolidated to top of the pipe.