Numerical Simulation Study of Shield Tunnel Construction Under Canal in Water‐Rich Sand Layer

To address the amplified ground deformation, the difficulty of controlling shield construction parameters, and the pronounced seepage‐related risks associated with twin earth pressure balance (EPB) shield tunneling beneath a canal and a mid‐channel divider island in water‐rich sandy strata, this study is based on Phase I of Nantong Metro Line 1 in China. Physical and mechanical parameters of the water‐rich sandy strata are obtained through field sampling and laboratory testing. A three‐dimensional staged construction model is then established in FLAC3D to examine the effects of key construction variables on ground deformation, identify critical control targets, and analyze the response of the pore water pressure field to construction disturbance. The results show that ground settlement is governed by the superposition of plastic zones and the cumulative effect of volume loss induced by twin‐tunnel construction, and exhibits a segmented pattern consistent with the engineering boundary conditions. Settlement peaks tend to occur at the divider island, riverbanks, and transitional construction sections. The effect of excavation face support pressure on settlement is nonlinear, both underpressure and overpressure amplify settlement, but the adverse effect of overpressure is more pronounced. In canal sections, synchronous grouting pressure exhibits a compensation threshold, beyond which excessive uplift of the riverbed and a higher risk of differential deformation occur. While limiting uplift, a grouting pressure of 0.2 MPa provides relatively stable settlement control. Construction‐induced pore water pressure disturbance is concentrated mainly in the vicinity of the excavation face, and transitional sections are more prone to hydraulic gradient concentration. These findings clarify the mechanism of ground deformation during twin EPB shield tunneling beneath canals in water‐rich sandy strata and provide useful reference for shield parameter design, monitoring layout, and engineering risk assessment in similar projects.