The Mechanism of Explosion Funnel Formation Considering the Dynamic and Static Time Sequential Action of Charge Blasting

The theory of explosion funnel is a fundamental research work in the field of blasting engineering. A thorough understanding of the formation mechanism of the explosion funnel can contribute to enhancing the blasting theory, optimizing the blasting parameters, and providing better guidance for field operations. By utilizing an improved double-exponential type explosive load function and explosion gas pressure equation of state, this study comprehensively analyzes the loading characteristics of explosive stress wave and explosion gas. Furthermore, a joint loading model considering both kinetic and static time sequential effects of blasting was constructed. Then, discrete element numerical simulation was conducted to investigate the fracture development within the rock mass of the explosion funnel as well as examine the crushing and throwing process. The results demonstrate that the size of the blasting funnel formed by using the explosive load loading model considering the dynamic-static time-sequence effect of packet blasting is more consistent with the field test results, and it can better reflect the formation and evolution of the fracture of the rock body being blasted and the throwing effect of the fragments. During the formation of the explosion funnel, both the explosive stress wave generated by the charge and explosive gas have distinct effects on rock fragmentation. The explosive stress wave exhibits a high loading rate and acts for a short period, resulting in micro-fractures near to the explosion source. At the same time, the reflection and tension on the free surface form a "spalling fall" failure. In contrast, the blast-generated gases primarily cause long radial fractures in regions farther away from the blast source while simultaneously propelling fragmented rock mass outward for throwing. These gases not only exert quasi-static effects but also possess certain degrees of dynamic effects, prolonging the action time of blasting vibration and intensifying velocity peaks during such vibrations. Fracture development can be roughly categorized into three stages based on their time sequence and causes: fractures induced by explosive stress wave, fractures caused by explosive gas, and fractures resulting from deformation energy release.