Deformation analysis of buried subsea pipeline under different pressure-reverse​ fault displacement loading paths

Abstract

The combined action of subsea seismic faults and pressure loads can cause pipelines to reach the limit state. Consequently, various failure modes, such as global buckling and system collapse, can occur. In this study, the deformation of a buried subsea pipeline under different pressure-reverse fault displacement loading paths is investigated using the nonlinear vector form intrinsic finite element (VFIFE). To quantify the damage to the pipeline and identify its failure modes under accidental reverse fault displacement, the loading path ‘fault displacement → internal/external pressure’ was analysed first. The post-earthquake resumption and reconditioning of unpressurised and pressurised pipelines, respectively, are evaluated based on the performance criteria in terms of strain and deformation. The corresponding loading paths are simplified as ‘ambient hydrostatic pressure → fault displacement → operation pressure’ and ‘operation pressure → fault displacement → external over pressure’. Moreover, the residual bearing capacity, weak position, and possible failure behaviour of the pipeline are comprehensively analysed for all subsequent external overpressures. The results show that the loading paths have a significant effect on structural responses, particularly on the elasto-plastic deformation. The two yield bends of a deformed pipeline under fault displacement are dangerous regions. Their inadequate relative residual strength leads to several successive local collapses and determines the occurrence and direction of buckling propagation during the subsequent external overpressure. The previous internal pressure has a significant influence on the residual capacity and failure modes of the pipeline, particularly the strain hardening effects with the influence of large seismic faults. The critical points of the first local collapse have specific characteristics, and the minimum residual resistance to external over pressure occurs when the maximum flattening parameter is 15% under initial fault displacement. The results of this study can guide the development of seismic design methodologies and engineering practice for buried subsea pipelines.