Attenuation Characteristics of Blasting Stress Under Decoupled Cylindrical Charge

Decoupled cylindrical charge structure is widely used in contour blasting to reduce overbreak and control rock damage, which is critical to the safety and efficiency of rock excavation. The blasting effect strongly depends on the blasting stress acting on the rock to generate cracks along the connecting line of boreholes. The blasting stress decays with distance in rock mass, so its attenuation significantly affects the blasting effect. The attenuation characteristics of blasting stress under different decoupled cylindrical charge structures are, accordingly, necessary to be investigated. In this study, physical model blasting tests under different filling mediums and decoupling ratios were conducted, and strain gages and a sonic tester were used to evaluate the blasting stress response and block damage. A numerical model was developed and verified to simulate the same tests and some other tests with additional decoupling ratios. The results show that filling medium and decoupling ratio play important roles in the attenuation characteristics of stress peak, which are analyzed and attributed to the different peak pressures and loading rates of the borehole wall pressures. A modified numerical model combined with response surface method was then developed to study the independent and interactive effects of static pressure, peak pressure (P), loading rate (L), and velocity of detonation (v) on the stress attenuation index (α). The results indicate that static stress has little effect on α in the elastic stage. α decreases with increasing P and v, and decreases with decreasing L. The effects of P and L on α are weakened with increasing v. Finally, based on a theoretical model of cylindrical charge, the results are further analyzed. The results show that the blasting stress for water decays more slowly than that for air, especially in low v.