A series of large-scale shaking table tests were conducted to investigate the dynamic response and damage characteristics of the variable- single pile foundation in liquefiable soil-rock interaction strata under seismic loading. The test results show that the seismic responses of the excess pore pressure ratio under seismic excitations are divided into four stages, among which the difference in the sustained liquefaction stage is the most significant. Pile acceleration amplification is governed by dual coupling effects of soil-pile interaction and structural stiffness. The pile body bending moment distribution features dual-peak characteristics, the largest peak arises at the soil layers interface, while the other peak occurs at the variable-section. Increased seismic excitation accelerates the liquefaction of the saturated sand layer, yet simultaneously slows down the dissipation of the excess pore pressure. As the seismic excitation increases, the acceleration response and displacement response of the pile top are most significant, though maximum bending moment positions remain stable. The stress overrun damage occurs gradually in the variable- zone under strong earthquakes. Based on the analysis results and the Fourier spectrum modal characteristics of the pile top, the damage mechanism of the pile body is revealed and verified. This study will provide an essential reference for further understanding the seismic response and damage of the variable- single pile foundation in liquefiable soil-rock interaction strata.

The construction of large-span and variable- foundation pits in silty soil is challenging. Soil creep often leads to engineering problems such as excessive settlement, uneven settlement, and slope instability. This study proposes a new construction method, which is suitable for the inconsistent bottom elevation of a foundation pit by taking the long-span and variable- foundation pit in Nanjing as an example. The construction process parameters were determined based on ABAQUS, and the accuracy of the numerical model and safety of the construction method were verified by field monitoring. The results show that foundation pit deformation increases with the distance between the supporting erection and the step length. Basal uplift decreased with an increase in excavation distance in the shallow area. The influence of the steel support erection time within 12 h on the foundation pit deformation was the most evident. The proportion of creep deformation in the foundation pit deformation on the early excavation side was approximately 21.6%, which was higher than that on the late excavation side. The location of the soft soil layer has an evident influence on the deformation of the foundation pit, and the creep deformation can reach 11% of the total displacement when it is located at half of the excavation depth.