Lateral cyclic interaction between catenary riser and soft seabed: Fid-Bau Portal

Lateral cyclic interaction between catenary riser and soft seabed

Wang, Li-zhong / Li, Kai / Yuan, Feng

Highlights•We modeled a large-scale 3D experiment about the riser/clay seabed interaction under lateral repetitive loading.•The increase of pipe embedment in different locations along the pipe near the touchdown zone under lateral interaction is observed, as well as the trench profile and the development of the touchdown zone.•The development of TDZ (touchdown zone) during cyclic interaction was observed.•A soil crust was found after combination of lateral and vertical cyclic interaction.

AbstractThe cyclic movement of a riser at the touchdown zone (TDZ), which involves complicated pipe–soil interaction, is critical to its long-term safety. Most previous studies have focused on the pipe–soil interaction of the riser in the vertical plane at the TDZ. Therefore, we conducted laboratory tests to investigate the pipe–soil interaction during lateral cyclic pipe movements and the influence of seabed evolution around the TDZ on the following vertical cyclic pipe movements. At the TDZ, the bell mouth shape of the clay bed and ladle-like shape of the pipe were observed during lateral cycling. The movement trajectory of the pipe as well as the gradual penetration process was recorded, which may be mainly attributed to the lateral ploughing and soil softening around the pipe. The test dynamic embedment factor (ratio of the dynamic embedment and static embedment) was 1.7–2.7. The enlargement of the TDZ during cycling was measured, which was mainly related to the movement of the trench surface point. The increase in the undrained strength of the soil at the TDZ after dynamic tests proves that a crust of soil was formed beneath the pipe owing to consolidation during cyclic pipe–soil interaction.