Abstract: Accurate assessment of the development of soil resistance acting on the pipe during large displacement lateral movement is an important prerequisite for the design of deep-water pipelines. Those pipe-soil interaction problems for light pipes, scraping across the seabed at very shallow depth, have been extensively studied. However, for heavy pipes characterised by diving downwards and getting buried by seabed soil, relevant studies are rather scarce, either in physical or numerical modelling. This scarcity is due to potential instability from extremely sufficient deformation such as soil collapse, as well as high computational cost. This work presents the first systematic numerical analysis of the lateral pipe-soil interaction for heavy pipes in undrained clay using sequential limit analysis (SLA). The evolution of pipe invert trajectory and pipe-soil lateral resistance during lateral movement are examined, and the V-H (pipe weight-lateral soil resistance) yield envelopes at different locations are derived as well, in order to explore the feature of lateral behavior of heavy pipes. It is found that the displacement required by heavy pipes to reach a residual state, characterised by nearly constant lateral soil resistance, is several times greater than that for light pipes. Even after reaching this state, three types of soil failure mechanisms still exist, and the influence of key parameters is analyzed. Finally, a residual resistance assessment model for heavy pipes is proposed, along with a discussion of its applicability.

Key words: subsea pipelines, large deformation analysis, soft clay, pipe-soil interaction, limit analysis