Experimental and numerical study on the effect of water-decoupling charge structure on the attenuation of blasting stress

The blasting fracturing technique is one of the most promising options for enhancing the permeability of reservoir rock masses in the exploitation of petroleum, coal, uranium and other deep resources. The increase in permeability strongly depends on the shock wave acting on the reservoir rock mass to create a fracture network surrounding the blasthole, which is significantly affected by the decoupling coefficient of the charge. This paper studies the effect of the water-decoupling charge structure on the distribution of blasting stress, as well as the morphology of blasting-inducing fractures. In this work, physical model experiments of water pressure blasting on cement mortar blocks (3.1 m x 3.1 m x 1.0 m) are first conducted to study the attenuation law of explosive stress along the radial direction under the condition of four different water-decoupling coefficients of the charge (i.e., 1.0, 1.79, 2.57 and 3.29). In addition, a square numerical model with one circular blasthole is modeled with a particle assembly based on the discrete element method to simulate the same water pressure blasting tests as those performed in the physical model experiments. The results from the physical model tests and numerical simulations both show that the attenuation amplitude of the peak value of the explosive stress wave along the radial direction first decreases and then increases as the water-decoupling coefficient of the charge increases. In particular, the numerical results also reveal that the distribution range of the fracture network is strongly related to the attenuation of the blasting stress. In comparison with the other three water-decoupling coefficients tested in this paper, 2.57 proves to be the best coefficients for inducing the most extensive fissure distribution from the blasthole. Thus, in water pressure blasting, be an optimal decoupling coefficient for receiving the best blasting effect must exist, and selecting an appropriate water-decoupling coefficient for blasting is beneficial for enhancing reservoir permeability.