Study on the efficiency of energy transfer in the blasting with different coupling mediums for deep rock mass excavation

Abstract

Geostress diminishes the energy utilization of explosives in deep rock mass blasting excavation. The water as a coupling medium in borehole is advantageous to improving the blasting effect and energy utilization in deep rock mass blasting due to its good load transfer effect. However, the theories of water-coupling blasting (WCB) for the deep rock mass excavation are imperfect and the relevant parameters are determined empirically with reference to the standards for air-coupling blasting (ACB). This study focuses on the differences in energy transfer between WCB and ACB. Based on the superposition of blasting stress and geostress, the failure characteristics and energy distribution were investigated under different charging structures and geostress levels in WCB and ACB for deep rock mass excavation. The results reveal that, in both WCB and ACB, as the increasing geostress, the energy consumed in the crushed zone remains relatively constant, while the energy consumed in the crack zone decreases, and the energy consumed in the elastic vibration zone increases. Furthermore, when the geostress is below 40 MPa, it has barely effect on the total energy transferred into the rock mass, but adjusts the proportion of effective energy to ineffective energy. The percentage of total energy transferred into the rock mass in WCB is about triple that in ACB. The effective energy declines with the increasing geostress, while ineffective energy shows the opposite trend. Further, an interesting finding is that the ratio of effective energy and ineffective energy in WCB compared to those in ACB increases with the increasing decoupling coefficient at a geostress of 20 MPa. Compared to the condition of smaller decoupling coefficients, the advantages of WCB over ACB is more obvious under larger decoupling coefficients. Meanwhile, the energy associated with the blasting cavity and blasting vibrations in both WCB and ACB was also discussed. Ultimately, the reliability of this study has been tentatively confirmed by combining theoretical analysis with numerical simulation results.