The interaction of reverse faults with flexible continuous pipelines

Abstract

Permanent ground displacements due to earthquake faulting may induce large deformation and loading of a buried pipeline. In particular, a pipeline crossing a fault rupture emerging at the soil surface will be subject to a combination of bending and/or axial compression or tension depending on the form of the fault displacement, the dip angle and the direction of the pipe with respect to the fault. This complex combination of loadings may be sufficient to cause disruption to the pipeline supply or leakage of product and so has potential for large financial and/or environmental impact. In this paper, the response of buried flexible pipelines crossing reverse fault ruptures has been examined using centrifuge modelling. A reverse fault is actuated in the 20th-scale model at an initial fixed dip angle in the bedrock and the fault rupture is seen to propagate upwards through a layer of sand towards the soil surface. Pipelines were buried in the sand layer to typical embedment ratios and their response was monitored as the fault displacement increased monotonically. Primary data capture was by the use of image analysis: semi-cylindrical modelm pipelines were placed at the front-face of the model and digital images were captured during the loading event. This allowed pipeline deformation patterns and thereby bending moment distributions to be calculated throughout the fault rupture event. Results are presented to show the effect of pipeline diameter, stiffness and embedment depth on the performance of buried pipelines during reverse and normal faults. In particular, it is shown that additional embedment of the pipeline is detrimental to its performance due to the additional confining effect of the soil which changes the relative pipe­soil stiffness.