Control effects of soil reinforcement on underlying metro tunnel deformation and influenced zone induced by deep excavation in soft strata

The commonly used soil reinforcement method is selected, and the finite element numerical method is used to study the influences of soil reinforcement in the pit on the deformation characteristics of the underlying metro tunnels caused by excavation. By defining the index of deformation control efficiency, the tunnel deformation control effect is characterized, and considering the deformation control effect and engineering economy together, the suggested scheme for soil reinforcement form and strength in the pit is given. Then, by using the above scheme, the control effect of soil reinforcement on the influenced zone induced by excavation is studied. There sults indicate that the control effect of the overall reinforcement is better than the strip-shaped reinforcement and the skirt-border reinforcement on the plane, and vertically the effect of layered reinforcement is better than the mixed reinforcement and the plate-type reinforcement. The tunnel deformation control efficiency increases non-linearly with the strength of reinforced soil, and there exists an optimal value for reinforced soil strength. After the soil in the pit is reinforced using the suggested overall reinforcement on the plane and the mixed reinforcement vertically (the reinforced soil strength below the base slab is 2.0 MPa, and that above the base slab is 0.5 MPa), the heave deformation of the underlying tunnel is significantly reduced, the distribution characteristics of the tunnel heave and the mode of influenced zone are changed, and the scope of the influenced zone is reduced.