Experimental study on decoupled charge blasting-induced crack propagation with parabolic shaped charge

In this study, a new parabolic shaped charge structure is proposed to realize bidirectional blasting in coal mines. To examine the fracture characteristics of rock mass induced by shaped charge structure under explosion load, a dynamic caustic experimental system is adopted. Further, the blasting-induced damage distribution characteristics of rock mass caused by different decoupling coefficients are investigated. Using polymethyl methacrylate (PMMA) as the experimental material, a two-dimensional model is established. AUTODYN, an explicit dynamics simulation program, is used to examine the initial crack generation process under shaped charge blasting. The stress wave propagation rule and the relationship between blasting damage and decoupling coefficient are explored. The results show that the parabolic shaped charge structure can control the explosion energy distribution and reduce the surrounding rock damage. When the decoupling coefficient is 2, the main crack length is optimum. During the crack propagation process, the growth rate and stress intensity factor of the main crack of the specimen show an oscillatory downward trend. Two stress concentration points are generated on either side near the main crack, forming the initial crack. When the decoupling coefficient is less than 2, long cracks exist in both the shaped and non-shaped charged directions, and the energy gathering effect is poor. When the decoupling coefficient is greater than 2, the energy gathering effect is obvious, but the main crack length is shorter.