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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
Engineering and Physical Sciences Research Council.