A new hybrid model for rigorous analysis of buried pipelines under general faulting accounting for material and geometrical non-linearities with focusing on corrugated HDPE pipelines

Earthquake-induced Permanent Ground Deformations (PGD) can be occurred due to fault movements, land sliding or liquefaction-induced soil displacements. This kind of deformation could significantly affect underground lifelines, such as buried pipelines. To assess the integrity of the pipelines against fault deformations, it is important to quantitatively evaluate the interaction between the pipelines and the surrounding soil. The simplified analysis procedures for buried pipelines crossing active faults given in the major seismic design guidelines for pipelines consider some bilinear force-displacement relationship curves to represent the soil-pipeline interaction. In a case of fault's large movement or existing relatively soft soil, the soil adjacent to the pipe could behave more in a nonlinear fashion and then affects the pipe's response and also changes the pipeline-soil interface behavior significantly. In this study, the effect of soil non-linearity as well as pipe's geometric and material non-linearities due to large ground deformations on seismic performance of buried pipelines were investigated. A new hybrid approach was developed to reduce the number of degrees of freedom of the soil-pipeline system accounting for rigorous soil-pipeline interaction. The approach combines the finite-element method (FEM) which models the pipe itself as well as the near-field soil around the pipe and the scaled boundary finite element method representing the far-field soil beyond the soil near-field. The behavior of pipeline embedded in the near field soil is modeled using large deformation shell elements, while the segment located far away from the fault, is considered as elastic beam elements. The proposed method was used to evaluate the maximum strains for the fault-crossing steel and High Density Polyethylene (HDPE) plane and corrugated pipes subjected to various fault movements. Parametric responses for different fault crossing angles, fault displacements and pipe diameters have been presented.