Methods for Accommodating the Classical Problem of Differential Movement in Buried Pipeline Systems

This paper serves as a practical guide on widely used methods and considerations to either accommodate or resist differential movement in buried pipeline systems. Differential movement is a classical problem that is frequently encountered when designing pipeline systems. Many of the options discussed will apply to both differential vertical settlement and to differential soil movement in the horizontal direction. Products discussed include flexible push-on joints, flexible restrained joints, ball joints, expansion joints, flexible couplings, and flexible pipe. Several pipe materials are compared including reinforced concrete, ductile iron, fiberglass, concrete cylinder, HDPE, welded steel, and PVC. Considerations discussed include spacing and location of flexible joints, determining allowable deflection, the use of software programs to predict the location and extent of differential settlement, ground improvement in areas subject to settlement, and appropriate backfill materials in areas where differential settlement is expected. The information presented should be of interest to pipeline designers, specification authors, operating personnel, and maintenance personnel.