Trench width in firm, stable ground will generally be determined by the pipe size, although the width may need to be increased depending on the compaction equipment, or to allow soil compaction between the pipes if two or more pipes are laid in the same trench.
Excessive runs of open trench should be avoided to minimize such problems as trench flooding, caving of trench walls and the freezing of trench bottom and backfill material, and to minimize hazards to workmen and traffic. The recommended minimum length of trench opening for each placement of continuous lengths of fused pipe, assembled above the trench, should be compatible with the pipe size and trench depth.
When the trench sidewalls are significantly sloped, somewhat shorter trench openings may be used. When space or ground conditions do not permit these suggested trench openings, the pipe lengths may be joined within the trench, using a joining machine or flanged couplings. When bell-and-spigot jointed pipe or flange-end pipe is used, the trench opening needs to be only long enough to accommodate placement and assembly of a single pipe length.