Experimental Modeling of the Unburial Behaviour of Pipelines

摘要

This paper is concerned with the interaction of a buried pipeline and the surrounding soil during various unburial processes. This follows a three year research program at Oxford University investigating mechanisms of pipeline unburial including upheaval buckling and pipeline floatation. The results include 2D plane strain uplift tests where a section of pipe is pulled upwards through soil, with the resulting forces and displacements being measured. A loose fine uniform sand is the focus of the study as this is often found in the North Sea and also reflects the soil conditions after pipe installation such as by jet trenching. The soil was tested in a dry state to benchmark drained capacities and in a saturated state to explore rate dependent responses. Particle image velocimetry was used to identify failure mechanisms at different depths as the pipe is pulled from the soil. A second theme of larger scale experiments, using a slender length of pipe, was also carried out to identify 3D effects that might not be captured in the conventional 2D tests. One set of experiments was carried out to determine the axial buckling load of a pinned and buried strut. The tests explored responses in dry sand and saturated sand showing that buckling loads are a function of soil cover depth. Further work was carried out in a specially designed pipeline testing tank (8m long) to explore buckling and floatation responses of a long slender pipe. The experiments were instrumented so that pipe displacements along the length were acquired as well as loads applied to one end of the pipeline. Summary conclusions from the work so far are presented.