EXPERIMENTAL INVESTIGATION ON SCOUR AROUND MARINE PIPELINES IN SILT BEDS BY JET TRENCHING

Jetting power has been applied more and more frequently to create trench in the seabed to bury cables or pipelines under a protective layer of sand in offshore engineering. However, there are still several key problems to be understood further and solved both in their design and operating. This study investigates the topographic deformation due to the scour of silt beds which lie below marine pipelines and are impinged by moving two jets in a model experimental system. The response of silty sea beds was also examined during the experiment. The important parameter that influences the trenching performance, the jet velocity, was studied. The speed of the jet horizontal motion was varied to examine its effect on the scour profile. By presenting the variation of a scour profile with time after impingement, the change process was analyzed. The asymptotic scour profiles were found to be very similar when made non-dimensional, and a function was employed to describe the non-dimensional profile. The results of the above work will permit a better understanding of the mechanisms controlling the performances of underwater trenching by jet trenching machines.