Lubrication mechanisms and their influence on interface strength during installation of subsurface pipes
McGillivray, Catherine Black
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Pipe jacking, has seen a rise in popularity, particularly in urban areas where infrastructure does not permit cut-and-cover methods. As pipe jacking has becomes more commonplace, engineers are pushing the limits of the technology more and more by designing longer drives in more difficult ground conditions. Lubrication is essential to reduce the frictional resistance generated at the pipe-soil interface. Even though lubrication is widely utilized, there is not a clear understanding of the conditions required to obtain the full benefit of lubrication. This dissertation focuses on bentonite slurry characteristics and interface behavior under different lubricating conditions with the goal to further the understanding of the mechanisms responsible for the large friction reductions observed in the field. An interface shear device capable of measuring interface behavior on pipe surfaces was used to perform tests under two lubricating conditions. Pipes were sheared against a mixture of sand and slurry and the effect of the slurry was quantified. In another series of tests, slurry was injected at the pipe-soil interface. An axisymmetric interface shear device was developed to further investigate the lubrication mechanism associated with injection of slurry into sand. The device was designed to inject slurry through injection ports built into a shaft displaced within a sealed sand-filled chamber. A series of tests were performed on dry sand as well as sand where water or slurry was injected during shearing. The effect of sand type and viscosity are also investigated. Findings from the experimental studies are related back to full-scale behavior with the objective of assessing the lubrication methods and their effectiveness. A rational procedure for predicting non-lubricated and lubricated jacking forces is proposed to optimize design and serve as a framework for evaluating jacking forces in the field.