Numerical Simulation and Deformation Control of Shield Tunneling Through Soft Soil Layer Pre-reinforcement

Relying on the shield tunnel project in the Chuang-Ju section of Foshan Metro Line 3, the surface settlement and tunnel deformation under different reinforcement methods were obtained by numerical simulation, and the deformation law of the shield when crossing the full-section soft soil layer was studied. A set of suggestions for shield tunnel safety crossing reinforcement is proposed, and the simulation results are verified by combining with the field measurement. The research shows that when the shield is advancing in the full-section soft soil stratum, the surface settlement, tunnel vault settlement and horizontal convergence value all increase continuously, which mainly occur when the shield passes through and after the shield tail segment is protruded, and it is also the main scope of action of pre-reinforcement; the impact of the leading tunnel on the surface settlement is greater than that of the trailing tunnel; when the shield passes through the unreinforced soil layer, the maximum values ​​of surface settlement, tunnel vault settlement, and horizontal convergence are 27.7 mm, 14.28 mm, and 10.57 mm, respectively. The deformations of the pre-grouting reinforcement are 57.0%, 66.6%, and 61.0% of the unreinforced ones, respectively. When the triaxial stirring piles are used for pre-reinforcement, the deformations are 32.1%, 48.5%, and 43.0% of the unreinforced ones. The pre-reinforcement can effectively control deformation, and the deformation control of the triaxial stirring pile is better than that of the advance pre-grouting reinforcement. When the ground environment in the shield tunnel is complex and the ground reinforcement conditions are not available, it is recommended to use advance pre-grouting reinforcement to control the surface settlement and tunnel deformation.