When pile foundation is encountered in the process of shield tunneling, it is necessary to cut off the pile foundation that affects shield crossing construction. It is significant to evaluate the influence of pile cutting on surrounding foundations and buildings. Taking the pile foundation reinforcement project of Nanjing Metro Line 7 undercrossing Fujian Road as an example, the finite element method is adopted to analyze the influence of shield crossing and cutting pile on the surrounding stratum, pile foundation and cap beam system. In addition, the influences of pile cutting depth, soil reinforcement and shield crossing way on the axial stress of the pile foundation were discussed. The results show that: Pile cutting induced by shield crossing and soil excavation can cause the settlement of the soil above the tunnel and the rebound of the soil under the tunnel, leading to the distribution of negative friction on adjacent pile beside the residual pile. Moreover, the force of the cover beam near the residual pile is reversed, i. e., the upper edge is in compression and the lower edge is in tension. While the soil chamber pressure can lead to compression inside the adjacent pile and tension outside the pile around the residual pile. Therefore, the stress of the pile during the shield crossing needs to be recalibrated. Furthermore, the smaller the pile cutting depth, the more load the adjacent pile bears. The soil reinforcement enables the residual pile to bear more load and results in a smaller impact on the deformation of the surrounding soil and the adjacent pile. The two piles cutting will lead to an increase of the axial stress on the residual pile top, but the stiffness adjustment effect of cover beam on the adjacent piles is basically unchanged. The study can provide relevant reference for the design and construction of the shield crossing pile project.

Soil liquefaction is a prevalent seismic hazard. However, current laboratory and model experiments studying the dynamic characteristics of sand liquefaction struggle to accurately represent the actual soil liquefaction process. The computational fluid dynamics (CFD) coupled with discrete element method (DEM) simulation method can accurately simulate various soil-water coupling problems. The CFD-DEM flow-solid coupling module facilitated the exchange of mechanical information between the commercial discrete element software PFC3D and the open-source computational fluid dynamics software OpenFOAM. The feasibility of this approach was confirmed through particle underwater free sedimentation experiments. Calibration of numerical sand specimens with dynamic characteristics of real saturated sand was conducted using PFC3D software through simulated laboratory cyclic triaxial tests. Based on the existing parameter information and the coupled simulation method, a site liquefaction model of saturated sand was established. The simulation results indicate that the discrete element method (DEM) can replicate laboratory sand liquefaction experiments, and the calibrated parameters can be applied to site liquefaction simulations. The consistency between the sedimentation velocity of a single particle and theoretical solutions validates the accuracy of the CFD-DEM coupling method. Under a peak acceleration of 0.25g, liquefaction occurs at various depths, and the ratio of excess pore pressure does not exceed 1 during liquefaction. The cumulative excess pore pressure increases from shallow layers to deep layers. After liquefaction, the soil strength gradually recovers from bottom to top, and the soil structure in the re-consolidated site shows a trend of homogenization.