Current pipe-soil interaction models for unburied offshore pipelines have generally been developed empirically on the basis of experimental data with little theoretical basis. Hence there are difficulties in transferring these models to conditions other than those from which they were derived. In an attempt to improve this situation, a series of pipe-soil interaction tests was performed using calcareous soil on the beam centrifuge at The University of Western Australia. An elasto-plastic model for pipe-soil interaction has been derived from these tests, comprising: a linear relationship between pipe vertical resistance and penetration depth; a parabolic shaped yield surface in vertical-horizontal load space; and a plastic potential with similar form to the yield surface. This model has been calibrated using the centrifuge test data. Predicted results from the new model show good agreement with the experimental data.
Unburied pipelines have been widely employed in transporting oil and gas products from offshore fields to onshore processing plants. The cost of a pipeline represents a significant proportion of the development budget of a new hydrocarbon field. To minimise the costs, the selection of pipe on-bottom weight, as determined by geotechnical stability analysis, is critical. As a consequence, a considerable amount of research work has been conducted world wide into pipe-soil interaction of unburied pipelines, the principal studies being: the PIPESTAB project, AGA project and DHI project (Wolfram et al, 1987; Allen et al, 1989; Verley et al, 1994). Pipe-soil interaction models were proposed (Wagner et al, 1987; Lieng et al, 1988; Brennodden et al, 1989; Brennodden et al, 1992; and Verley et al, 1994), based on the data from large-scale model tests in the separate projects. Some of the models have been incorporated in design programs. The general form of these models is shown in Eq. (1).