Determination of Safety Factor for Rock Mass Surrounding Tunnel by Sudden Change of Equivalent Plastic Strain in Strength Reduction Method

The safety factor of rock mass surrounding tunnel can be determined using the strength reduction method (SRM), furthermore, it is very important to solve the criterion of critical state. For the stability estimation of rock mass surrounding tunnel, there is need to discuss that it is preferable to use the same criteria for the slope stability, such as non-convergence of finite element calculation, penetration of plastic strain and sudden change of horizontal displacement. The safety factor can be determined by sudden change of equivalent plastic strain in relationship between a reduction coefficient of strength parameter and equivalent plastic strain. This method is based on the elasto-plastic finite element method (FEM) and the SRM by ABAQUS and Mohr–Coulomb yield criterion. Simulation results using this method show how a safety factor varies with geometries, friction angles and cohesions for circle and square tunnels. Simulation results also show the safety factor varying with quality change of rock mass, pore water pressure and tunnel depth.