Study on type I fracture characteristics and double K toughness model testing of anchored sandstone

Abstract

Abstract Engineering rock masses prone to type I tensile cracks due to excavation unloading can be reinforced with anchor rods to increase the proportion of stable fracture stage and reduce the probability of brittle failure. However, based on the traditional strength analysis method, the relationship of σ-ε is difficult to fully explain. Therefore, it holds crucial engineering and theoretical value to explore the failure mechanism of anchored rock based on the characteristics of fracture mechanics. In this paper, the fracture toughness of rock with different bolt crack relative positions and preloads is tested through speckle light measurement. The double K fracture criterion is introduced, and the mechanism of crack arrest and toughening of bolts is discussed based on the net stress intensity factor theory. The research results indicate that the closing force generated by the lateral action of the anchor rod significantly reduces the range of rock strain localization. While it has a limited effect on delaying rock cracking, it can effectively delay crack propagation and intersection. The initiation and instability fracture toughness of rocks show a logarithmic increasing trend with the shortening of the relative position between anchor bolts and cracks and the increase of preload. Increasing the net stress intensity factor at the crack tip of the bolt improves the rock crack initiation and unstable fracture toughness. After anchoring, the rock crack initiation and unstable fracture toughness increased by 90% and 130%, respectively. The length and time of the stable crack growth stage increased by 50% and 70%, respectively.