Experimental Study of Pile Group Bridge Failure Mechanism Caused by Liquefaction-Induced Lateral Spreading

In this paper, we study the seismic behavior of pile group bridges in inclined liquefiable soil and reveal the failure mechanism by conducting large-scale shaking table tests. Two bridge models were supported by two foundations: a group pile in an inclined liquefiable site and a rigid foundation. Typical results of the model test under a strong event (Tabas 0.3 g) are illustrated, and the effects of soil-group pile-bridge interaction are explored. The inertial and kinematic effects of the pile-pier curvature are evaluated, and the seismic failure mechanisms of the pile-bridge system are revealed. The results demonstrated that the near-pile shallow soil exhibited significant shear dilation response during the occurrence of strong earthquakes, which induced acceleration spikes for both soil and structure. The interaction state was soil pushing the pile and pile pushing the soil during the first and the subsequent strong earthquake, respectively, due to the bridge P-Delta effect. The liquefaction-induced lateral spreading increased the kinematic effect and reduced the inertial effect on the pile head curvature. In addition, the inertial effect on the pile curvature decreased gradually from the shallow layer to the middle of liquefiable soil, while the kinematic effect increased gradually. The results also demonstrated that the rigid foundation assumption overestimated the acceleration demand of the bridge during strong earthquakes; however, it seriously underestimated the lateral displacement. Finally, the lateral spreading shifted the vulnerable position of the pile group-pier system from the pier bottom to the pile head and bottom, and the leading piles sustained more damage than the trailing piles.