Axial Distribution and Radial Transition Characteristics of Explosive Loading on a Blasthole Wall in Rock Blasting

In rock drilling and blasting, explosion shock waves propagate along the axis of the blasthole as the explosive reaction progresses. Meanwhile, detonation products expand rapidly in the radial direction, resulting in rock crushing and fragmentation. However, few studies have comprehensively investigated explosive loading on the blasthole wall, considering both axial and radial mechanical behaviors. The present study analyzes impact pressures recorded in rock drilling and blasting based on onsite experiments. The axial distribution laws of explosive loading under different initiation locations are then analyzed numerically and theoretically. Furthermore, the influences of charge structure and rock property on explosive loading are investigated in view of the interaction between the air shock wave and the rock mass. Finally, an improved prediction method for explosive loading on a blasthole wall is proposed. The results show that explosive loading is nonuniform along the radial direction of the blasthole. In the cases of bottom and midpoint initiation, peak explosive loading first increases and then stabilizes. For dual initiation, shock wave collisions occur in the middle section of the charge, resulting in a sudden increase in explosive loading. Furthermore, the explosive loading experiences a significant increase when transmitted from the air shock wave to the rock mass. The charge structure, rock property, and explosive type influence the radial loading increase ratio. As the decoupling ratio increases, the radial loading increase ratio gradually increases, while the pressure after the incident wave decreases. This leads to a reduction in explosive loading on the blasthole wall. For different rock types, the pressures after the incident wave are at the same level. Nevertheless, as the wave impedance of rock mass increases, the radial loading increase ratio increases accordingly, leading to an increase in explosive loading. Considering both axial and radial loading characteristics, an improved prediction method for explosive loading on the blasthole wall is proposed. Furthermore, the method is validated against existing experiments, with errors ranging from 0.13% to 11.22%, demonstrating its reliability.