Effect of Varying the Depth of Burial of Submarine Pipeline on Wave Forces in Well Graded and High Hydraulic Conductivity Sand

Abstract

Information on wave force variation due to different burial of submarine pipeline is essential in order to choose its appropriate depth of burial. It is a function of wave climate, water depth, geotechnical and hydraulic properties of the seabed soil, etc. To solve this problem, physical model investigations were carried out in a wave flume to assess the change in the horizontal and vertical hydrodynamic forces on a submarine pipeline for different depths of burial. The marine sand is well graded and has hydraulic conductivity of 1.84 mm/s. It is found that the horizontal force reduces nonlinearly with increase in depth of burial. 75% of the magnitude of the horizontal force reduces by just burying the pipe, when compared to the horizontal force on the pipeline placed on the seabed. The vertical hydrodynamic force is smaller for half buried pipe and increases for just fully buried case due to the significant change in the magnitude as well as the phase difference between the pore water dynamic pressures. For any burial depth and for a constant wave height, increase in wave period has noticeable increase in the vertical wave force than the horizontal wave force. The horizontal wave force dictates the stability of the submarine pipeline, when it is placed on the seafloor. For buried pipeline in sand of high hydraulic conductivity, the upward wave force dictates its stability. Workout example is also presented as a ready reference for the readers of this article.

Keywords:

• Submarine pipeline
• well graded soil
• high hydraulic conductivity
• horizontal and vertical wave forces
• optimal burial depth