Past seismic events have shown that caisson quay walls are susceptible to severe damage during earthquakes, underscoring the importance of assessing their seismic behavior. However, very limited studies have been conducted on the soil-structure-water interaction of the caisson-ground system during earthquakes. This study will investigate the seismic response and failure mechanism of a caisson through a centrifuge shake-table test. Specifically, the seismic response results of the backfill, the caisson, and the subsoil are discussed; an acceleration integration method for identifying permanent displacement to estimate the backfill deformation is proposed; and a phase analysis of the seismic response of the caisson-ground system is conducted. It is found that the liquefaction of the backfill results in a substantial increase in the dynamic earth pressure behind the caisson. The failure mode of the caisson is lateral movement accompanied by slight tilting and continuous rocking vibrations. The proposed acceleration integration method can effectively estimate the deformation and lateral spreading of backfill. Phase analysis results reveal the relationship between the failure of the caisson-ground system and seismic action.

The presence of frozen soil layers leads to stratification in soil stiffness, thereby influencing the dynamic response of pile foundations in seasonally frozen soil regions. This study investigated the dynamic response of pile-soil interaction (PSI) systems in such regions. A reduced-scale (1/10) model of a pile group with an elevated cap in railway bridges was subjected to shake-table testing. During these tests, measurements were taken of soil and pile accelerations, displacement time histories, and pile strain. The acceleration amplification factor (AMF) and response spectrum of the soil and pile foundation were analyzed based on these data. Additionally, the pile-soil interaction and the dynamic shear stress-strain relationship of the soil were investigated. The experiment indicated that the presence of a frozen soil layer alters the energy dissipation order of the pile-soil interaction system. This leads to a weakened dynamic response of the pile foundation. Furthermore, the seasonally frozen soil layer acts as a filter for high-frequency ground motion, thereby mitigating resonance between ground motion and the pile foundation, ensuring the protection of the pile foundation. However, the significant stiffness contrast induced by the seasonally frozen soil can pose a threat to structural safety under increasing peak ground acceleration (PGA). As PGA increases, there is a transition from linear to nonlinear interaction between the pile and soil, initially affecting the unfrozen soil layer, then the frozen-unfrozen transition layer, and ultimately impacting the seasonally frozen soil layer.

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.