Sequential limit analysis of pipe-soil interaction during large-amplitude cyclic lateral displacements

A newly developed sequential limit analysis (SLA) technique is used to perform large-displacement numerical simulations relevant to thermally-induced lateral buckling of untrenched subsea pipelines. A rigid plane-strain pipe segment, partially embedded in undrained clay, is subjected to cyclic lateral displacements with amplitudes of up to eight pipe diameters. A constant vertical dead load is applied to the pipe during each lateral sweep, but in some analyses this load is varied from one sweep to the next. The SLA method directly models the evolution of the soil surface profile, including active and dormant berms, and incorporates strain softening behaviour caused by soil remoulding. Comparisons of the numerical results with published centrifuge model test data, for a range of loading cases, are provided in terms of the pipe invert trajectory and lateral soil resistance. There is good overall agreement between the numerical and experimental results, demonstrating the suitability of SLA for solving such problems. Detailed aspects of the cyclic loading behaviour are discussed with reference to soil failure mechanisms and bearing capacity failure envelopes for combined vertical and horizontal loading. Finally, two brief parametric studies are used to explore the effects of the initial pipe embedment and vertical loading history on the subsequent lateral loading behaviour