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UBC Theses and Dissertations

Soil restraints on steel buried pipelines crossing active seismic faults Monroy-Concha, Manuel


The quantification and prediction of soil restraint on buried pipelines are essential for the design of pipeline systems crossing seismic faults, and in turn to reduce the risk of pipeline damage due to geotechnical earthquake hazards. Full-scale soil-pipe interaction tests were undertaken to better simulate the mobilization of soil restraints under controlled conditions and to provide insight on a number of currently unresolved technical issues that so far have been investigated only based on small-scale tests. In particular, an existing full-scale testing chamber was significantly modified to simulate pipeline breakout from its soil embedment on one side of a strike-slip fault and on the footwall side of a reverse fault in an effort to characterize lateral, combined axial and lateral, and vertical oblique soil restraints. The experimental system was also used to assess the effectiveness of reducing soil loads on pipelines using geotextiles. The following was noted: (1) approaches based on limit equilibrium reasonably well predict maximum values of lateral soil restraint for shallow pipelines backfilled with sand, with mixture of crushed gravel and sand, and with crushed limestone; (2) the lateral soil restraint on pipes in geotextile-lined trenches increased with increasing relative pipe displacement and could even be higher than the restraint without the geotextile lining. A procedure was developed to capture this behaviour; (3) experimental and numerical results for geotextile-lined trenches suggest that the shear resistance is not controlled solely by the geotextile interface; as such, there is no clear benefit in using geotextile-based mitigation measures for reducing soil loads; (4) the results from tests on combined axial and lateral soil restraints provided limited clarification on whether or not these soil restraints should be considered independent for fault crossing designs. This was due to the difficulty in selecting an axial soil restraint value to anchor existing soil restraint interaction relationships. No axial soil restraint tests were conducted in this work; and (5) values for the maximum vertical oblique soil restraint diminish as the inclination of the angle of breakout of buried pipelines increases with respect to the horizontal.

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