Use of Visual Methods to Investigate Influence of Installation Procedure on Pipe-Soil Interaction

Abstract

The results of four laboratory tests on a very flexible pipe (standard dimension ratio of 83) buried in sand are reported. Photographs of sand particles and the pipe in the plane of the cross section were taken through the glass face of the test rig. The measured displacements during installation and subsequent surcharge loading were compared with measurements of circumferential pipe wall strains to determine the effects of installation on pipe performance. Two installations involved sand being placed carefully around the pipe profile, one with compaction of the sand in layers and the other without compaction. The final two installations concerned sand either being scattered uniformly around the pipe or being heaped (uncompacted) on one side before leveling. The results indicate that pipe performance is greatly affected by the installation procedures used. In particular, asymmetrical filling and compaction result in lateral displacement and a difference in pipe support on either side of the pipe. Lack of haunch support because of poor material distribution during initial sidefilling results in a tendency to displacement, and hence strain concentration, at these points. Thorough compaction of the side-fill at the spring lines was found to cause the pipe to be raised from its bedding, with the pipe subsequently deforming into the void thus formed. The pipe wall strain profiles were shown to correlate well with the displaced pipe profile, and predictions of deformed shape can thus be made with care. The movement of individual sand particles indicates well the way in which the soil support is derived.