Failure mechanism of fully grouted rock bolts subjected to pullout test: Insights from coupled FDM-DEM simulation

Fully grouted rock bolts are widely used in mining, tunneling, and pit support, and thus the study of their anchorage performance is beneficial for optimizing the anchorage system design. In this study, an FDM-DEM coupled numerical model is established to simulate the whole process of rock bolt pullout test and to investigate the failure mechanism of fully grouted rock bolts. The accuracy of the model is verified by comparison with existing laboratory test results. Virtual experiments are conducted on different models by eliminating the anchor plate, changing the layered rock strata condition, and adding bolts. The results show that the presence of an anchor plate will reduce tensile stress to restrain the rupture of surrounding rock and thus improve the strengthening effect. Due to the different bond strength and tensile strength of the soft and hard rock mediums, the layer sequence of the rock strata affects the maximum pullout force. The upper-soft and lower-hard composite rock strata (S-HCR) exhibits single-cone damage while the upper-hard and lower-soft composite rock strata (H-SCR) exhibits double-cone damage. The superposition effect of the anchor group on the stresses and displacements is the reason leading to the reduction of the maximum load-bearing capacity of the rock bolts.