Analysis of the Limit Support Pressure for Curved Tunnel Faces Considering the Soil Arching Effect

On the basis of silo theory, the limit equilibrium method, and the soil arch effect, an irregular inverted truncated pyramid wedge body model is proposed to address asymmetric jacking force and overexcavation issues in curved tunnels. Analytical solutions for the vertical stress exerted by the soil above the curved tunnel arch and for the limit support pressure at the tunnel face are derived. The model effectiveness is validated through numerical simulations and field monitoring and compared with the existing straight tunnel model. Furthermore, the effects of shear strength parameters, tunnel geometry parameters, and additional ground loads are analyzed. The results indicate that the proposed model is more suitable for curved tunnels than current models. When the effective internal friction angle φ′ is large, the additional ground load minimally impacts the vertical stress at large burial depths. Specifically, when the burial depth ratio z/D > 5 and φ′ > 25°, the additional ground load has a negligible influence on the limit support pressure. Moreover, the influence of overexcavation on the limit support pressure of curved tunnels is obvious. When the curvature radius R < 500 m and φ′ < 15°, the limit support pressure is significantly affected by the curvature radius.