Probabilistic Assessment of Lateral Pipeline–Backfill–Trench Interaction

Abstract

Trenching and backfilling of pipelines is a common practice for physical protection. In seismic regions, buried pipelines may be at risk of fault displacement that causes massive lateral pipe movements and jeopardizes pipeline mechanical integrity. The lower stiffness of the remolded backfilling material relative to the native ground has a significant impact on lateral soil resistance against large pipeline displacements that are rarely considered in current design practice. Finding a safe, reliable, and cost-effective trench configuration is a key aspect of design practice that is affected by pipeline–backfill–trench interaction. In this analysis, a probabilistic approach was used to investigate trenching/backfilling effects on the response of buried pipelines to large lateral displacements. A three-dimensional beam-spring model subject to a strike-slip fault was developed and the effect of trenching/backfilling was incorporated using nonlinear springs. Two limit state criteria were set to identify the safe and failure regions. A code was developed using Python programming software to perform iterative analysis by variation of pipe specifications, native and backfill soil properties, trench width, trench depth, and lateral displacements. The first-order reliability method (FORM) was used to estimate the exceedance probability of failure using the identified limit states, and the results were validated against published studies in the literature. The study showed that the trenching/backfilling of pipeline results in lower lateral soil resistance against displaced pipe. In addition, it was observed that the advantage of load reduction could be used to mitigate trench dimensions and reduce construction costs without sacrificing safety and integrity requirements.