STUDY ON THE EFFECT OF SEABED SOIL ON RELIEVING DAMAGE OF SUBMARINE PIPELINES IMPACTED BY DROPPED OBJECTS

Seabed plays an important role in the analysis of submarine pipeline subjectd to impact loads. Based on the coupled Eulerian-Lagrangian method (CEL method), a finite element numerical model is established to simulate the soil deformation involved in the impact process. Meanwhile, physical model tests are carried out. The numerical simulation results show good agreement with test results. Aiming at seabed in clay, a series of influence factors on pipeline damage have been analyzed, including the seabed flexibility, soil property, embedment depth, friction, and dropped object shape. For pipelines resting on seabed surface, part of the impact energy will be dissipated through pipeline global deformation due to bed flexibility, which can relieve the pipeline local damage. For buried pipelines, either the normally consolidated clay or the homogeneous clay is considered. The safe embedment depth of these two conditions differs significantly. Considering the aboved soil conditons, an embedment depth of approximately two meters can provide effective protection for pipelines. The friction coefficient between the dropped object and soil has influence on the dissipation of impact energy and pipeline damage, which is signficant when the embedment depth exceeds one meter. Dropped object in sharp shape can casue servere damage because of less resitance from soil. Besides, there are some differences between deformation characteristics of pipelines, which are influenced by dropped objects in various shapes. The research results are expected to provide reference for risk assessment and safe embedment depth design of submarine pipelines.