Double-K fracture toughness mechanism of mode I failure in anchored rocks with prefabricated cracks under different loading rates

Traditional strength analysis methods, which primarily rely on the relationship of σ - ε , are insufficient to fully elucidate the failure mechanisms of anchored rocks. Investigating the failure mechanism of anchored rocks through the lens of fracture mechanics holds significant engineering and theoretical value. In this study, the fracture toughness of rocks with different lithologies under varying loading rates was tested using the Digital Speckle Correlation Method (DSCM). The mechanisms by which anchor rods inhibit crack propagation and enhance rock fracture toughness were also explored. The results indicate that the closure force generated by the lateral action of the rock bolt significantly reduces the extent of strain localization. Although this lateral action has a limited effect on delaying crack initiation, it effectively retards crack propagation and coalescence. As strength and loading rate increase, both the initial and unstable fracture toughness increase logarithmically. After anchoring, the initial and unstable fracture toughness increase by 90% and 130%, respectively, while the length of the stable crack propagation stage decreases by 50% and the propagation time increases by 70%.