Performance Evaluation of Tunnel Support System in Jointed Rock Mass by Numerical Simulation: A Case Study

In this study, a numerical verification of the performance of preliminary tunnel support systems suggested by rock mass classification methods is performed. The Rock Mass Rating (RMR) method and the Quality Index (Q Barton) show a succession of a moderately jointed and jointed quality of Kherrata Tunnel 3. The numerical assessment combining the Finite Element Method (FEM) with the Discrete Fracture Network (DFN) models; involves the jointed area of the tunnel, in which the Voronoi model represents the joints distribution. During numerical simulations, particular attention focused on the evolution of the total displacement and the extension of the plastic zone. In addition, a parametric study was carried out to study the effect of the length and spacing of rock bolts on tunnel deformation. Results showed that the combined FEM and DFN models represent a solution for the stability analysis of underground excavations. The Voronoi model is suitable for representing the global distribution of joints in the rock mass. The parametric study carried out revealed pertinent conclusions. Thus, increasing the length of bolts (4 m to 6 m) decreases the total displacement of the tunnel; and reduces the extension of the plastic zone. However, the spacing between rock bolts does not improve the stability. The empirical method remains a reliable tool for the recommendations of preliminary support systems.