Effects of layered liquefiable deposits on the seismic response of an underground structure

Soil liquefaction poses significant threat to underground structures in seismically active areas. This paper present a detailed numerical investigation on the seismic response of underground structures in horizontally layered liquefiable grounds. A comprehensive plasticity model for large post-liquefaction shear deformation of sand is used for modelling the liquefiable soil layers. A technique of combining beam elements with quadrilateral elements is employed to simulate the response of reinforced concrete structure. Shallow buried underground structures in three typical soil profiles, including a layered liquefiable ground, a homogeneous liquefiable ground, and a homogeneous non-liquefiable ground, are analyzed under seven scaled ground motions, amounting to a total of 21 dynamic calculations. The numerical results show that the existence of a liquefiable layer passing through an underground structure can have detrimental effects on the seismic response of the structure, compared to underground structures embedded either in homogeneous liquefiable and or non-liquefiable ground, causing the structure to suffer larger deformation, bending moment, and shear force. The soil-structure interaction and inertia effects are analyzed to provide explanation for the seismic response of the underground structures.