Numerical analysis of the impact of excavation for undercrossing Yellow River tunnel on adjacent bridge foundations

Taking the twin-tunnel shield tunnel of the urban rail transit in Lanzhou City as an example, this article applies the hardening soil small criterion and utilizes finite element software to simulate the excavation process of the undercrossing Yellow River tunnel. The analysis focuses on the deformation effects and axial force variations of nearby bridge foundations in three directions: vertical to the tunnel, along the tunnel, and the vertical direction. The simulation results are compared with monitoring data. The findings indicate that shield tunnel construction increases the deformation of bridge foundations in the vertical and tunnel directions, while mitigating the deformation in the vertical direction. The influence is more significant as the distance between the tunnel and the foundations decreases. The redistribution of stress due to soil disturbance causes foundation deformation, and the magnitude of foundation deformation reflects the extent of soil disturbance. The simulated vertical displacement of the pile head is consistent with the trend observed in the field measurements. The simulation results generally align with the conclusion that the tunnel has minimal impact on the soil beyond a distance of 3–5 times the tunnel diameter