Contribution of Lateral Earth Pressure Resistance to Restrain Horizontal Thrust in Buried Pipelines

Current restrained joint design theories for different pipe materials depend on two primary mechanisms, frictional and lateral earth pressure, to resist the horizontal unbalanced thrust forces at a horizontal bend, valve, tee or other similar source of thrust in a buried pressure pipeline. The frictional resistance mechanism relies on the friction and adhesion resistance at the pipe-soil interface, while the lateral pressure resistance in current practice is generally assumed to be from passive pressure resistance. The contribution of frictional resistance in resisting the thrust forces in a horizontal bend was the subject of a paper presented by the task committee at the ASCE Pipelines 2010 conference. A similar, critical examination of the contribution of the lateral earth pressure resistance to resist the unbalanced thrust forces in a horizontal bend will be the primary objective of this paper. As thrust acts on a buried pipeline, the pipe in the vicinity of the source of thrust moves both longitudinally and laterally, relative to the axis of the pipeline. The lateral earth pressure component of resistance arises from the lateral component of the pipe movement into the surrounding soil. The lateral pressure component is directly considered in AWWA design manuals for some pipe materials, but not others. When lateral earth pressure is directly considered, it is generally assumed to be derived from passive resistance; other forms of lateral resistance mechanisms, such as bearing capacity/lateral flow of soil around the pipe, are not considered. This paper examines the theoretical and experimental basis for the current design approaches related to the use of lateral earth pressure for the thrust restraint design. It will assess recent developments in soil-structure interaction and load-deformation behavior and their possible use in establishing a common and rational approach to incorporating the lateral earth pressure component into thrust restraint design.