Numerical Investigation of the Vertical Settlement of Seabed Pipelines Under Lateral Cyclic Loading in Clay

As exploration moves into deeper water, offshore pipelines, generally laid on the seabed, are an increasingly significant component of offshore hydrocarbon developments. Seabed pipelines are mainly subjected to the wave loading, which causes vertical settlement of pipelines. In this study, the vertical settlement of seabed pipelines under lateral cyclic loading in normally consolidated clay is investigated through the large deformation finite element (LDFE) analysis with the Coupled Eulerian Lagrangian (CEL) technique. The effects of strain rate dependency of the undrained shear strength and soil remoulding are considered by adopting an extended Tresca clay model during lateral cyclic loadings. Firstly, the LDFE results are compared with centrifuge test results and published LDFE data, showing a good agreement. Then, a series of LDFE cases are conducted to investigate the effects of pipe weight, lateral load amplitude, soil sensitivity, and the initial trench depth on the accumulated vertical settlement of pipelines under lateral cyclic loading. The LDFE results show that the affected clay zone around the pipeline due to the lateral cyclic loading is highly remoulded, and the initial trench depth has a great effect on the accumulated vertical settlement of pipelines. With the increasing number of lateral load cycles, the accumulated vertical settlement of pipelines first increases and then decreases. A modified expression is proposed to estimate the ultimate vertical settlement of pipelines in clay.