Chapter 40 PROBABILISTIC FAULT DISPLACEMENT ANALYSIS FOR A PIPELINE SYSTEM

Permanent ground displacement (PGD) caused by coseismic fault displacement in earthquakes presents a significant hazard for buried pipelines. Although large displacements are not frequent, they can result in pipeline buckling, rupture, and failure. In order to evaluate the relative likelihood of failure for multiple pipeline fault crossings, a natural gas pipeline operator performed a simplified Probabilistic Fault Displacement Hazard Analysis (PFDHA) for a number of potentially high hazard fault crossings in Southern California.

As a part of the PFDHA, quantitative estimates of the displacement magnitude and probability of ground movement were defined for nine faults. These were combined with nonlinear elastic-plastic finite element analysis (FEA) to determine the probability of varying levels of strain in the pipeline at each crossing location. Based on the analysis presented, the expected compressive/tensile strain to failure can be incorporated to evaluate the fault rupture likelihood associated with each pipeline-fault crossing. By reviewing the analysis results of this and similar analyses, the operator can screen and rank the relative criticality of locations in the pipeline and/or determine if fault displacement mitigation is necessary.