Lubrication mechanisms and their influence on interface friction during installation of subsurface pipes.

摘要

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 an essential component 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 evaluation of slurry preparation procedures was conducted to establish a consistent procedure for mixing large batches necessary for interface shear testing. Viscosity-concentration relationships were quantified for different commercial bentonite products.;An interface shear device capable of measuring interface behavior on curved surfaces was used to perform tests under two lubricating conditions. In both cases, sand was sheared against pipe coupons cut from pipes commonly used in the tunneling industry. In the first set of tests, pipes were sheared against a mixture of sand and slurry and the effect of the slurry was quantified. In the second set of tests, slurry was injected at the pipe-soil interface more in line with the application procedure in the field.;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.;The mechanism of friction reduction utilizing bentonite slurry is identified as an effective stress reduction at the interface. Successful lubrication is achieved by appropriately adjusting slurry properties to restrict drainage into the soil and prevent pressure dissipation. An existing theoretical prediction model for non-lubricated jacking forces was adapted to account for the use of slurry lubrication. Finally, 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.