Seismic performance of pile group-structure system in liquefiable and non-liquefiable soil from large-scale shake table tests

Observations from previous strong earthquakes reported severe damage of piles installed in different soils, particularly liquefiable saturated sand deposits. This paper examines the seismic performance of pile group structure system in liquefiable and non-liquefiable sand deposits using large-scale shaking table tests, and discusses the possible failure modes of pile foundation in liquefied site and non-liquefied site. Accelerations and strains of piles, and lateral displacements and accelerations of model soil were recorded. The measured piles' accelerations and strains were used to calculate their bending moment profiles during the shaking, while the soil dynamic shear strain - shear stress curves were obtained using measured soil accelerations. In addition, characteristics of dynamic responses for liquefied and non-liquefied sites were evaluated by comparing trends of acceleration and lateral displacements of model soil. Furthermore, the failure mode for pile foundations in liquefiable and non-liquefiable site were elucidated from the observed responses of the structure-pile foundation. It was found that (1) the stiffness of liquefied site degraded more significantly (compared to non-liquefies site) due to increase in pore water pressure, but the non-liquefied site experienced higher amplification of acceleration; (2) large lateral spreading did not occur in the liquefiable site experiment due to the horizontal surface of the underlying stable (non-liquefied) soil; (3) profiles of pile bending moment differed for liquefied and non liquefied sites for the same excitation, which impacted the permanent deformation of the piles. The test results in this study can be used to validate related numerical models.