ABSTRACT
Rigid pipes do not deflect enough for deflection to affect soil pressure against the pipes. The soil is a load on the pipes. Rigid pipes include Portland cement concrete pipes (both reinforced and unreinforced) and vitrified clay pipes. Other pipes may be rigid under certain conditions. Cement mortar lined and cement mortar coated (CML/CMC) pipes perform as rigid pipes when buried in loose soil because pipe stiffness is relatively greater than soil stiffness. In densely compacted soil, CML/CMC pipes may be flexible, or, according to some designers, may be semi-rigid. Design of concrete pipes is described in the Concrete Pipe Design Manual, published by the American Concrete Pipe Association [ACPA (1993)]. Pipe strengths are specified by standards. The ACPA has wisely left to the manufacturer the responsibility of making pipe that meets the standards. In general, performance limit is longitudinal cracking of the pipe wall due to internal or external pressures.
