A Quantitative Method for Predicting the Fragmentation Range in Rock Blasting Based on the Dynamic Coupling Effect of In Situ Stress and Explosive Load

Abstract

The rock blasting crush zone and fracture zone develop in the direction of major principal stress under the influence of in situ stress. However, there is still a lack of an accurate calculation method for predicting the dynamic influence of in situ stress on the range of these two zones. This paper examined the failure process of the crush zone and fracture zone under dynamic load through the dynamic stress paths of a rock mass. A novel quantitative method for the size of these two zones based on the dynamic coupling effect of in situ stress and explosive load was proposed. Its effectiveness was verified by single-hole blast cracking experiments. The results showed that the method can quantitatively describe the blast damage zone under coupled loading. The accurate determination of the attenuation coefficient (α) of the blast wave in the rock mass is the key to realizing the quantification. In this paper, the inverse proportional function relationship between α and proportional distance (r/a) can be well used to describe this relationship. As the in situ stress increases, the area of the crush zone and the fracture zone produced by the explosion gradually reduces. As the unit in situ stress increases, the degree of reduction in these two zones also reduces. However, due to the difference between r/a and α, this rule is more obvious in the fracture zone. According to the calculation, the radius limit of the fracture zone is lowered by around 50% and the normal stress increases to approximately one times the dynamic tensile strength when the rock mass with a tensile strength of 10.8 MPa is blasted by an emulsion explosive. As the explosion damage range in the low-in situ stress (<10 MPa) area varies greatly with increasing in situ stress, this phenomenon of damage range reduction in the low-in situ stress area requires special attention.