Axial sliding resistance of partially embedded offshore pipelines

This paper presents the results of centrifuge model tests and three-dimensional large deformation finite element (LDFE) analysis on axial pipe-soil sliding behaviour of partially embedded subsea pipelines. A 3Dre-meshingand interpolation technique with small strain (RITSS) approach was adopted using ABAQUS’s mesh-to-mesh solution mapping feature with the Cam-Clay model. The parameters studied include soil properties, interface friction coefficient, embedment depth and post-lay reduction in vertical load. Embedment depth and post-lay load reduction were found to exercise the strongest influence on the post-consolidation and sliding behaviour. Empirical relationships correlating centrifuge experiments and numerical modelling are proposed for the embedment enhancement factor in terms of the embedment and vertical load ratios, under conditions of very slow sliding, corresponding to the drained condition. For very fast sliding, corresponding to effectively undrained conditions, similar relationships involving embedment and vertical load ratios and interface friction coefficients are also proposed. Finally, the variation of embedment enhancement factor with sliding velocity is expressed in terms of a relative enhancement index, which can be adequately described by hyperbolic relationships for the complete range of consolidation history. These relationships provide a basis for the evaluation of embedment enhancement factor corresponding to an arbitrary sliding velocity, which can be used in routine analysis and design of as-laid underwater pipelines in soft clayey soils.