Behaviour of buried pipes and bored tunnels in sand
This thesis essentially reports an investigation of the behaviour of buried (0.12 to 0.25m diameter) single-walled PVC-U and vitrified clay pipes during installation in a uniform sand surround and when subjected to applied surface loading. An additional simple study of tail void displacements due to tunnelling in sand is also presented. Controlled laboratory tests were conducted in a glass-faced, steel-sided box. The buried pipes were installed perpendicular to the glass face and were subjected to static and cyclic loading, simulating increasing overburden stress and the passing of traffic over a shallow buried pipe respectively. The simulated shallow tunnel tests were also conducted perpendicular to the glass and involved withdrawal of the outer of two concentrically placed tubes. Photographs were taken of the sand particles and the buried structure in the plane of the cross section together with strain gauge readings on the pipe or tunnel wall throughout installation and loading/shield withdrawal. The resulting sand displacements are presented in the form of horizontal and vertical contour plots. Pipe deflections and volumetric and shear strain contours of the sand were also determined for the buried pipe tests. The shape of the deformed pipe and the imposed stress at the pipe springline were inferred from the pipe wall strains. During the PVC-U pipe tests, the deformation of the pipe caused the applied stress to be transferred to the sidefill via arching in the surrounding soil. This was associated with a reduction of applied stress reaching the pipe. Increasing the initial soil stiffness reduced the magnitude of the pipe and soil displacements and the stress carried by the pipe. Use of a vitrified clay pipe however, caused the soil surround to settle relative to the pipe. Soil shear strain contour plots are used to highlight the mechanisms of the transfer of applied stress onto, or away from, the buried pipes, and are related to the shape of the deformed pipe in the PVC-U pipe tests. The test data also allowed standard buried pipe design methods and installation procedures to be critically appraised. The soil movements recorded during the tunnel tests were shown to be similar to those recorded during the buried PVC-U pipe tests, indicating a similar soil loading transfer mechanism.