Development of Hazard Map for the Risk of Exceeding the Intolerable Liquefaction-Induced Settlement for a Power Transmission and Distribution System in Portland, Oregon

Liquefaction-induced settlement is one of the main geotechnical issues that may cause failure in the equipment (e.g., circuit breakers, transformers, liquid reactors, etc.) at the substations within a powerline system after earthquakes, and subsequently cause the lack of power supply in the area of service and the economic loss to the clients and the owner of the powerline system. In this paper, a simplified approach is presented to develop the hazard maps that quantify the risk of exceeding the intolerable liquefaction-induced settlement at 174 substations within a power transmission and distribution system in Portland, Oregon, under a magnitude (Mw) 9.0 Cascadia Subduction Zone (CSZ) earthquake scenario. The substations were categorized based on shear wave velocity measurements and geologic information. Probabilistic and deterministic seismic hazard analyses were performed to estimate the ground shaking intensities and the corresponding annual frequency of occurrence at each substation. Based on that, probabilistic liquefaction assessment was conducted to evaluate the liquefaction potential and estimate the liquefaction-induced settlement and the probability of exceeding the threshold value of the liquefaction-induced settlement. The results will be used in the structural, substation fragility analysis and risk assessment as part of the strategic asset management (SAM) study to prioritize the seismic risk reduction projects that will also provide optimum return on investment from the maintenance and capital spending perspectives.