An equivalent anchoring method for anisotropic rock masses in underground tunnelling

•An anisotropic constitutive model of layered rock masses is proposed and numerically implemented.•The equivalent anchoring parameters for bolted layered rock masses are studied based on the proposed model.•The equivalent anchoring method for bolted layered rock mass is proposed.•The Huashang Road tunnel in Wuhan China is simulated by the equivalent anchoring method. Rock bolting has been widely utilized for reinforcing underground openings, such as tunnels and mining. To ease the complexity of numerically simulating of the bolted rock mass, a novel method for equivalent anchoring simulates the reinforcement effect of the bolts by considering the anisotropic characteristics of the layered rock mass. The jointed material model in ABAQUS is improved by incorporating the anisotropy through the programming language FORTRAN. Based on the improved jointed material model, the equivalent anchoring parameters of the bolted layered rock masses are studied through a series of numerical tests. The numerical outcomes reveal that the improved jointed material model can be used to simulate the anisotropic features of the layered rock mass by comparing the classic and analytic solutions. The degree to which the supporting parameters affect the equivalent reinforcement performance are different in anisotropic rock masses, and the sensitivity of their influence is bolt length > bolt spacing > bolt diameter. Furthermore, an equivalent anchoring model for bolted rock masses (the formula of the improved parameter between the ratio of bolt length to tunnel diameter and the ratio of bolt diameter to bolt spacing) is proposed through numerical results analysis by the multiple linear regression method. An application case shows the field monitoring agreed well with the predicted vertical displacement of the tunnel demonstrating the feasibility of the proposed simulation method for the bolted rock mass. The results show the proposed method in this study can be conveniently utilized for efficient simulation of the mechanical behavior of bolted rock masses.