Face stability analysis of deep tunnels crossing water-rich weak zone

The deep tunnels are prone to mud and water inrush disasters when crossing water-rich weak zones. A good understanding the hydromechanical behavior of the water-rich weak zone in deep tunnels is the prerequisite for determining the limit support pressure on the tunnel face. However, the seepage forces within the water-rich weak zone are not well estimated in existing models. To overcome this, an analytical model is proposed in this study to determine the limit support pressure of a deep tunnel crossing the water-rich weak zone. The seepage force in the water-rich weak zone is obtained by solving a group of Laplace equations about the hydraulic head, avoiding complex physical and mathematical approximation in existing models. Besides, the seepage boundary conditions in the water-rich weak zone are considered at the nodes on the Neumann boundary and the Dirichlet boundary. The effectiveness of the proposed model is then validated by numerical simulations and engineering practice. It shows that the proposed model has higher accuracy and wider applicability in estimating the hydraulic head. The proposed model can be used for stability analysis of tunnel faces.