BUCKLING FAILURE ANALYSIS OF SUBSEA BURIED PIPELINE CROSSING STRIKE-SLIP FAULT

Long-distance subsea pipelines often inevitably pass through seismic faults which may impose great threats to pipeline safety, such as twist deformation, wrinkling and tensile rupture. The innovative vector finite element method (VFIFE) was used to analyze the buckling failure behavior of subsea buried pipeline crossing seismic faults. First, the calculation formula of the VFIFE 3D thin shell element were derived considering the material nonlinearity and a custom-made nonlinear pipe-soil interaction model was proposed for the shell element. Then we focused on solving the self-collision contact problem of the inner wall of the pipeline during its collapse and buckle propagation. A Fortran program as well as a corresponding post-processing program was developed. The computation models were verified through a comparison with the published results. A simulation of the buckling failure process of empty subsea pipeline under the strike-slip faults was carried out, and the influences of crossing angle, soil property and water pressure on the buckling failure behavior were analyzed. The results show that the subsea pipeline can hold a higher capacity against fault displacements due to its small diameter-thickness ratio, high steel grade and softer surrounding soil. Under the combined action of lower external pressure and strike-slip faults, the deformation of the subsea pipeline is S-shaped and the buckling failure is dominated by excessive bending caused by fault displacements. The buckling mode is that the compression side of the second bend or both the two bends undergo obvious invagination and the cross-section deformation is elliptical. Under such loads, the smaller the crossing angle, the smaller the critical fault displacement for buckling failure of the pipeline; the higher the strength of the surrounding soil (sand>clay>slit and sand), the more serious the bending deformation and the smaller the critical fault displacement for buckling failure. Under the combined action of high external pressure and strike-slip faults, the buckling failure is dominated by external pressure. The main mode is that the first or second bend collapses firstly and then buckle propagation occurs. Under different combinations of water pressure and fault displacement, the degrees of destruction of the pipeline are different. Moreover, the collapse position, the direction and range of buckle propagation, and deformed cross-sectional shape exhibit different patterns. The results can be used to guide the seismic design and buckling prevention research of subsea pipeline crossing seismic faults. © 2022 Tsinghua University. All rights reserved.