Wave force variation due to burial of submarine pipelines in uniformly graded and low hydraulic conductivity soil

Abstract

One of the challenging problems in submarine pipeline technology is to understand how the wave force changes due to its burial in a typical soil. The wave force variation for different buried conditions of the pipeline depends on the wave height, wave period, water depth, engineering and hydraulic properties of the seabed soil, like hydraulic conductivity, porosity, and submerged soil density. Physical model investigations were carried out in a wave flume to assess the variation of the wave forces on a submarine pipeline for different depths of burial. Poorly graded marine sand with uniformity coefficient, Cu of 1.240 and low hydraulic conductivity of 0.286mm/s is used for the model seabed. It is found from this study that the horizontal wave force reduces non-linearly with increase in relative depth of burial of the submarine pipeline, whereas the uplift force increased up to half buried depth, beyond which it reduced with increase in depth of burial. For half exposed pipeline, the uplift force is almost double when compared to just buried pipeline in this soil type. A buried pipeline may experience partial exposure during storm events in coastal waters and hence it is appropriate to consider the uplift force conditions corresponding to partial exposure (e/D=0.5) in order to avert risk of pipeline ruptures. The results can be used for the range of normalized wave parameters selected for the study and for the reported soil type.