Modeling Large-Deformation Pipe–Soil Interaction for Heavy On-Bottom Pipelines in Clay

Reliable assessment of large-displacement pipe–soil interaction is essential for the controlled buckling design of deep-water pipelines. While extensive research has focused on light pipes, this paper shifts the focus to heavy ones. Using the sequential limit analysis approach, we model pipes laterally displaced in undrained clay with a maximum displacement range of up to 40 diameters, determined based on industry experience. Key parameters examined include pipe weight, initial embedment, soil strength profile, and strain softening effects. It was found that a residual state, characterized by nearly constant pipe elevation and lateral soil resistance, can only be reached at displacements exceeding 30 diameters by heavy pipes. Once this state is reached, the effect of loading history is minimal, as evidenced by the close alignment of vertical and horizontal load failure envelopes, which are well described by an elliptic equation. The study also identifies various soil failure mechanisms for heavy pipes, highlighting the difficulties in developing a simplified model for assessing pipe–soil resistance. A quantitative empirical model is proposed to evaluate soil softening at residual state.