This practice covers the proper methods of installing vitified clay pipe lines in order to fully utilize the structural properties of such pipe. The external loads on installed vitrified clay pipe are of two general types: (I) dead loads and (2) live loads. For pipes installed in trenches at a given depth, the dead load increases as the trench width, measured at the top of the pipe, increases. Live loads that act at the ground surface are partially transmitted to the pipe. Live loads may be produced by wheel loading, construction equipment or by compactive effort. Classes of bedding and encasements for pipe in trenches are defined as Class D wherein the pipe shall be placed on a firm and unyielding trench bottom with bell holes provided, Class C wherein the pipe shall be bedded in clean coarse-grained gravels and sands, Class B wherein the pipe shall be bedded in suitable material and Class A. Trenches shall be excavated to a width that will provide adequate working space, but not more than the maximum design width. Trench walls shall not be undercut. Bell holes shall be excavated to prevent point loading of the bells or couplings of laid pipe, and to establish full-length support of the pipe barrel. Final backfill need not be compacted to develop field supporting strength of the pipe. Final backfill may require compaction to prevent settlement of the ground surface.