Numerical simulations of pipe–soil interaction during large lateral movements on clay

Abstract

The soil resistance during large lateral movements of pipelines across the seabed is an important input to design solutions for the management of thermal and pressure-induced expansions. To investigate this behaviour, a large-deformation finite-element (LDFE) analysis method involving frequent remeshing was employed. The LDFE method allows the changing geometry of the seabed when disturbed by the pipeline to be incorporated. Also, the effects of strain rate and strain-softening on the undrained shear strength of the soil were accounted for. A back-analysis of a centrifuge modelling simulation was first performed, for validation, and then a parametric study varying the pipe weight and initial embedment was undertaken. The results show that a steady state is generally reached at large displacements, reflecting a balance between the growth of a soil berm ahead of the pipe and the softening of the disturbed soil. The initial breakout response matched well with previously established failure envelopes, and a new interpretation has been proposed to capture the large-displacement response. The ‘effective embedment' concept is used to rationalise the influence of the soil berm ahead of the pipe. This leads to simple new relationships for predicting the steady-state residual lateral resistance, which provide more accurate predictions of the LDFE response than previously established solutions. The complete load–displacement response over large movements was also shown to be well fitted by an exponential relationship, albeit for the specific case of lateral movements under constant vertical load.