Fluid-Soil-Structure Interaction in Liquefaction around a Cyclically Moving Cylinder

Coastal or offshore structures such as pipelines installed on the seabed are submitted to cyclic horizontal loads either by the direct hydrodynamic action of waves or through the cyclic movement of risers or flow lines transmitted by floating structures. In fine sandy or silty soils these cyclic loads can induce a liquefaction of the surrounding bed, which can play an important part in the processes of erosion, trenching, or self-burial of the pipes. As part of the LIMAS program, a full-scale physical model was built to study the fluid-soil-structure interaction with special emphasis on the conditions leading to liquefaction around a pipe instrumented with pore pressure sensors. The experiments indicate a development of excess pore pressure at the pipe-soil interface much higher than the effective overburden stress, and a lateral visualization provided evidence of the liquefaction of a soil band in the vicinity of the pipe. The penetration of the structure can be related to the phenomenon of liquefaction.