Parameter analysis of excavation face stability of shield tunnel under high water pressure seepage

Abstract

When a river-crossing shield tunnel is excavated in saturated soft clay strata, the fluctuation of the water level, the tunnel buried depth, and the physical properties of soil have a significant influence on the tunnel face stability. In this study, based on the basic theory of fluid-solid coupling of the surrounding rock soil, the fluid-solid coupling calculation method and the stability criterion of the tunnel face were used. The failure modes, deformation characteristics, and fluid-solid coupling effect were systematically investigated under different water levels, buried depths, diameters, and soil permeability coefficients when the excavation face was unstable. The results show that with the changes of water level, buried depth, and tunnel diameter, the collapsed body presents a logarithmic spiral distribution as the underwater shield tunnel face is unstable. The limit support force of the excavation face increases linearly with the rise of the water level, and the seepage force greatly influences the limit support force. For the deep-buried shield tunnel, the limit support force and maximum horizontal displacement of the excavation face change slightly due to soil arch effect. The soil arch effect can be used as the deep- and shallow-buried boundary of an underwater shield tunnel. As for the underwater shield tunnels with different diameters, the instability of excavation face first occurs at the lower part of excavation face. The face stability of underwater small-diameter shield tunnel is better than that of large-diameter one. In addition, the soil permeability coefficient has a weak effect on the tunnel face stability.