Finite element analysis of buried steel pipelines under strike-slip fault displacements

The present paper investigates the mechanical behavior of buried steel pipelines, crossing an active strike-slip tectonic fault. The fault is normal to the pipeline direction and moves in the horizontal direction, causing stress and deformation in the pipeline. The interacting soil–pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behavior and special conditions of contact and friction on the soil–pipe interface. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80), the paper focuses on the effects of various soil and pipeline parameters on the structural response of the pipe, with particular emphasis on identifying pipeline failure (pipe wall wrinkling/local buckling or rupture). The effects of shear soil strength, soil stiffness, horizontal fault displacement, width of the fault slip zone are investigated. Furthermore, the influence of internal pressure on the structural response is examined. The results from the present investigation are aimed at determining the fault displacement at which the pipeline fails and can be used for pipeline design purposes. The results are presented in diagram form, which depicts the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. A simplified analytical model is also developed to illustrate the counteracting effects of bending and axial stretching. The numerical results for the critical strain are also compared with the recent provisions of EN 1998-4 and ASCE MOP 119.