Deformation control performance of the clay shock method during shield tunneling in close proximity to existing structures

To investigate the effectiveness of the clay shock method in controlling stratum disturbance and deformation of existing structures induced by shield tunneling near existing structures, a laboratory model test system for mid-shield backfill grouting was developed. An orthogonal range analysis was conducted to evaluate the influence of slurry viscosity, stratum permeability coefficient, and grouting pressure on the final grouting time and final grout volume. Furthermore, a finite element numerical simulation model was established to simulate the shield shell-stratum annular gap filling effect during close proximity tunneling across existing structures and to assess the deformation control performance of the method. The results show that the final grout volume is positively correlated with both stratum permeability and grouting pressure, while the final grouting time is mainly governed by slurry viscosity and grouting pressure. In the case of undercrossing an existing operational tunnel, the clay shock method significantly mitigates construction-induced disturbance, reducing the maximum ground settlement by 52.9% to 60.6%, delaying the occurrence of differential surface settlement, and decreasing the final surface settlement by approximately 54%. Additionally, the clay shock method reduces crown and invert settlement of existing tunnels by an average of 46%, demonstrating effective deformation control. For the case of side-crossing bridge pile foundations, the clay shock method shows limited effectiveness in controlling vertical pile settlement; however, it significantly suppresses horizontal displacement, with a reduction rate of 7% to 20%, and also reduces longitudinal displacement by 6% to 14%. The research findings provide a reference for parameter optimization and practical engineering applications of the clay shock method in shield tunneling projects involving close-proximity crossing of existing structures.