Soil Displacement of Slurry Shield Tunnelling in Sandy Pebble Soil Based on Field Monitoring and Numerical Simulation

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter alpha was performed, revealing that as alpha increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter alpha decreases, the width of the settlement trough narrows, improving the settlement trough profile.