Nonlinear Numerical Simulation Method for Combined Supporting Structures of Steel Sets and Shotcrete in Tunnels

Combined supporting structures consisting of steel sets and shotcrete are widely used in underground tunnels when the geological conditions are poor, however, there exist many challenges to conduct nonlinear numerical analyses for them since the steel sets are always arranged densely. Therefore, an elastic damage constitutive model of the shotcrete considering the degradation of the strength and stiffness as well as the different properties of the tension damage and compression damage was developed based on the elastic damage theory. Then, a mathematical model of the steel set was presented considering its mechanical characteristics, and its mechanical action is simulated by superimposing its stiffness into shotcrete. All of these are incorporated into a self-developed FEM program to conduct nonlinear numerical analyses for the combined supporting structures of steel sets and shotcrete in tunnels. This method was applied in a circular tunnel and the bearing characteristics of the combined supporting structures were analyzed, which proved its rationality. This method has no necessity to establish complex solid models for steel sets and can simulate the damage softening phenomenon of shotcrete, which can provide an effective way to conduct nonlinear numerical analyses for combined supporting structures in actual engineering.