Assessing the range of blasting-induced cracks in the surrounding rock of deeply buried tunnels based on the unified strength theory

Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse, posing significant safety risks. However, previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress, especially that of the intermediate principal stress. The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation, and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load. Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress, intermediate principal stress, and detonation pressure, whereas negatively correlated with Poisson ratio and decoupling coefficient. The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior. The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress. As the in-situ stress increased from 0 to 70 MPa, the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.