Response of Horizontally Bent Buried Pipelines Subjected to Strike-Slip Faulting: A Numerical Investigation

Abstract

When traversing through an active strike-slip fault, buried pipelines may be subjected to permanent ground deformation (PGD), causing large strains in the pipeline during an earthquake. The presence of bends near the fault-crossing zones may further increase the strain in the pipe. Moreover, it is well acknowledged that bends are the most vulnerable location to earthquake damage, mainly when compressive strain develops due to PGD. Hence, most design guidelines recommend constructing pipelines without field bends, elbows, and flanges crossing the fault zone. However, it is not always possible to provide only a straight segment of the pipeline, especially for blind faults where the location of the faults is unknown. Hence, the present study aims to investigate the response of buried continuous steel pipelines with field bends subjected to strike-slip faulting by conducting an extensive parametric study. A three-dimensional pipe-soil interaction model is developed in a finite element framework for this study. The pipeline response in terms of its maximum von-Mises stress and maximum longitudinal stress and strain due to fault crossing is studied for various influencing parameters such as pipe bend angle, soil strength, pipe burial depth, and distance of the fault trace from the bend. Based on the results obtained, suitable relationships in terms of modification factors over the response of a straight pipeline as a function of a few critical parameters are determined using regression analyses. It is concluded that providing bends to the pipeline can significantly affect its structural response when subjected to fault displacement when the fault trace is close to the pipe bend. The primary outcome of this investigation would be to suggest a simplified methodology to estimate the response of pipelines having field bends while crossing fault lines from the response of straight pipelines in a similar scenario.