Study On Pipe-soil Interaction During Lateral Buckling Of Pipelines Unburied In Deepsea

The demand for oil and nature gas grows with the development of Chinese industry and the exploration gradually transfers to deep sea. Submarine pipeline is an important part of offshore production system. The continuous collection and transportation of oil and gas benefit from the safty of pipelines. The overall buckling is one of the main failure modes of submarine pipelines. Based on unit length of unburied submarine pipeline in deep sea, the lateral soil resistance to large displacement of cyclic motion has been tested in an experiment investigation. CEL?the coupled Eulerian-Lagrangian analyses? finite element method in ABAQUS is used to analysis lateral soil resistance when pipe is in the process of large displacement motion on the surface of soil. The results of experiment and FEM are compared. The theoretical derivation of key parameters in the process of overall buckling has been done. Three pipe-soil interaction models are used to simulate the first-order of overall lateral buckling to investigate the influence of the pipe-soil interaction. The main conclusions are as follows.?1?The rule of soil resistance changing with displacement of pipeline : When pipeline starts, the lateral soil resistance grows rapidly. The lateral soil resistance reaches an initial peak near the displacement of one diameter. Then the soil resistance grows slowly, tending to be stable to the end.?2?The deeper the pipeline initially embedded and the bigger the pipe diameter,The faster the lateral soil resistance grows with pipeline displacement and the greater the amplitudes of the peak at beginning and at the end are. Lateral soil resistance grows geometricly with the height of the soil berm.?3?During the large displacement lateral cyclic motion of pipeline,the soil berm accumulates and consolidates at the amplitude of buckling displacement.The pipe-soil interaction increases significantly when the pipe reaches the displacement amplitude again.?4?CEL?the coupled Eulerian-Lagrangian analyses?finite element method is applicable to analysis of pipe-soil interaction in large displacement. Results from a 2D continum finite element model are similar to the results of experiment.?5?Theoretical Research of the first-order of overall lateral buckling has been done. Formulations of [?_m]_min and [?_m]_min are derivated.[?_m]_min has nothing to do with the environment load, only depending on the properties and parameters of pipe section??6?Overall buckling FEM results show that:soil model with large deformation available performs strong resistance to pipeline buckling;soil model with small deformation available performs weak resistance to pipeline buckling;Rigid soil model has the weakest effect on pipe buckling. Stronger pipe-soil interaction makes larger[?_m]_min, larger safe buckling area and slower stress secend increasement.