Calculation of the safety thickness of water inrush with tunnel axis orthogonal to fault

When the tunnel face is close to the fault, it will destroy the existing groundwater system and cause the surge of water in the tunnel face or roof. In order to determine the thickness of water inrush prevention safety, when the tunnel axis is orthogonal to fault, the outburst prevention model for face and roof water inrush model are constructed. Based on the Sheorey model and Silo theory, the stress state at the fault location is determined. Based on the limit equilibrium method, a theoretical formula of minimum safe thickness is derived, and the sensitivity analysis of parameters is carried out. Finally, it is verified by an engineering example. The results show that (1) the minimum safety thickness increases with the increase of the fault zone size, and the influence is negligible when the fault size exceeds the limit value; (2) the limit value of fault dip angle is determined when water gushes from roof or face; (3) the frictional resistance coefficients of the fault and surrounding rock have great influence on the minimum safety thickness, but the cohesive force of surrounding rock has little influence; (4) the minimum safety thickness increases with the increase of water pressure and tunnel diameter. © 2021, Saudi Society for Geosciences.