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UBC Theses and Dissertations

Response of buried natural gas pipelines subjected to ground movement Weerasekara, Lalinda

Abstract

The performance of buried natural gas pipeline systems in areas subjected to ground displacements is an important engineering consideration since geotechnical hazards can be a major cause of damage to these utilities. With polyethylene (PE) pipes now becoming the industry standard for natural gas distribution systems, a detailed investigation into the interaction of these materials is needed to ensure that the response of both pipeline and soil components is properly understood during design. With this background, a detailed research program involving full-scale physical modeling has been undertaken at University of British Columbia (UBC) to study the effect of permanent ground displacements on buried PE piping. This thesis presents details on material properties, testing procedures and findings from laboratory full-scale tests performed to study the performance of number of buried pipe configurations applicable to field conditions. The results indicated that buried PE pipes subjected to relative soil movement in axial direction cannot be predicted using the simplified equations commonly used to capture the axial soil resistance in steel pipes. This is primarily due to complex pipe-soil interaction arising due to the flexibility and the non-linear material response of PE pipe, combined with dilation and arching effects from soil around the pipe. A new closed-form solution was derived to account the nonlinear material response of PE pipes. This solution provides the framework to obtain the response of the pipe (strain, force and the mobilized frictional length along the pipe) for a known relative displacement of the pipe. In branch pipe systems, the test results demonstrated that the physical location (branch pipe, trunk pipe or the tapping tee connection) of vulnerability would depend on relative pipe sizes, soil density, and boundary conditions. New analysis techniques were derived, and guidelines were proposed, to account the anchoring force offered by the tapping tee and the branch pipe in evaluating the performance of branch pipe configurations. In addition, technical details are discussed in relation to performance of the PVC protective sleeve and socket outlet tapping tees. These test results of straight and branch pipes would facilitate in developing a reliable database for calibrating/validating numerical and analytical models for potential future studies.

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