Multistep Pipe-Soil Interaction Analysis That Accounts for Liquefied Residual Soil Strength

Metro Vancouver plans to install twin 914-mm internal diameter sewer forcemains under the Fraser River. Liquefaction-induced permanent ground displacement presents a major seismic hazard to the pipeline. A pipe-soil interaction finite element model was built in Abaqus to verify the pipeline design. The pipeline was modeled using a beam-type element that can respond to bending loads with ovalization of the pipe cross section. Ground displacements were applied in multiple modeling steps to capture the anticipated loading sequence and permit the alteration of the soil restraint. Excess pore-water pressure generated during shaking was used to reduce the soil restraint provided by liquefied/partially liquefied soil along the alignment. Steel and HDPE pipeline materials were analyzed in the model. This paper presents the analysis methodology used to justify a pipe wall thickness increase from 6.4 to 9.5 mm in a portion of the alignment and the placement of a critical pipeline joint.