Shake-Table Test Study of Dynamic Response of Soil–Pile Interaction System in Seasonally Frozen Soil Regions

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.