Experimental and numerical investigation of crack propagation in bolting systems strengthened with resin-encapsulated rock bolts

Rock reinforcement design necessitates a clear understanding of the initiation and propagation of cracks in the bolting system. To better understand the mechanism, we performed laboratory pull-out tests on resin-encapsulated rock bolts. Numerical models on a 1:1 scale were built using the discrete element method. The microscopic parameters of the model were calibrated based on unconfined compression tests and ring shear tests. The model allows us to visualize the progressive failure of a bolting system strengthened with resin-encapsulated rock bolts and elucidates the role of the anchorage length in controlling crack propagation. Comparisons indicate that the physical and numerical results are consistent. The results show that increasing the anchorage length improves the bondability and strength of the bolting system and restrains the complete debonding of the rock bolt from the cement mortar. At the same time, it also facilitates the conversion of shear cracks to tensile cracks. However, the shear crack of the resin is the dominant effect in the bolting system. In addition, the results reveal how factors such as boundary confining pressure, resin thickness, and cement-mortar strength affect crack initiation and propagation.