Abstract
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.
Highlights
According to field observations, liquefaction seems to play an important part in erosion and stability problems for coastal structures, such as breakwaters or pipelines
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
Damgaard and Palmer (2001) discussed the order of magnitude of the different processes leading to the instability of pipes and found that the hydrodynamic forces necessary to laterally move a pipe resting on the seabed cause sediment transport and liquefaction before a significant movement of the pipe occurs
Summary
Liquefaction seems to play an important part in erosion and stability problems for coastal structures, such as breakwaters or pipelines. As part of the same LIMAS program, a series of tests corresponding to this second scenario was performed at the University of Grenoble These tests focused on fluid-soil-structure interaction and the simulation by use of mechanical actuators of the cyclic wave action on pipes resting on a sand bed. Pipe-soil interaction has been studied extensively by many authors, such as Lyons (1973), Lambrakos (1985), Brennoden et al (1986), Wagner et al (1987), Palmer et al (1988), Morris et al (1988) These authors demonstrated the process of self-burial of structures resting on the seabed induced by wave action. Such loading conditions do not represent exactly the hydrodynamic effects, they are interesting in order to understand the influence of the experimental parameters
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