Pipeline Geohazard Target Susceptibility Threshold – A Reliability-Based Rationalization

Pipeline geohazard assessment involves the delineation and quantification of threat severity associated with a suite of geohazard mechanisms deemed credible for a specific setting or project. The context for a typical assessment is loss of containment from the pipeline — an ultimate limit state (ULS) — considering individual geohazard mechanisms (e.g., landslide, fault displacement, rockfall, subsidence, etc.). To estimate the probability of loss of containment associated with a particular geohazard mechanism at a given location, the evaluation process can be partitioned into an estimate of the probability of occurrence of the geohazard mechanism at that location, and the conditional probability of loss of pipe integrity should the event occur. The product of these two probabilities is termed “susceptibility” expressed as loss of containment events per year at a given location. A typical approach to manage geohazards assessed in this way is to set a target susceptibility threshold to determine mitigation requirements to reduce the estimated susceptibility value for individual geohazards. The rationale for selecting a target susceptibility threshold value has been a topic of interest in recent pipeline projects in Canada. This paper demonstrates a reliability-based approach in rationalizing the selected pipeline geohazard target susceptibility threshold and linking geohazard assessment results to Quantitative Risk Assessment (QRA) of all threat categories in ASME B31-8S.