Study on the reinforcement mechanism of grouted bolts with or without prestress via the hybrid DEM-FDM method

Abstract

Rock bolts are an economical and effective reinforcement approach in tunnel engineering. The reinforcement mechanism and quantitative effect of prestressed and nonprestressed grouted rock bolts in tunnels are investigated in detail from micro to macro perspectives in this study through a proposed hybrid model combining the discrete element method (DEM) with the finite difference method (FDM) under the condition of plane strain. A new contact model is implanted into the DEM to reproduce the realistic rock characteristics and discontinuous deformation. Through the analysis of the bond breakage number distribution, the force chain, etc. after bolt installation, it is found that the stress state of the rock is greatly improved (i.e., in a safer state), and the crack is prevented from further coalescence due to bolt installation, especially in prestressed bolt cases. Furthermore, the presence of prestress in the bolt can greatly reduce the displacement increase in the reinforced region; however, the displacement at the tunnel wall in the prestressed cases is almost the same as that in the cases without prestress, which is consistent with the results from the theoretical model. For prestressed and nonprestressed bolts, the influence of the length and number of bolts on the micro- and macroscopic responses is finally investigated, and the minimum (optimal) length is suggested for the cases under the specific conditions in this study.