Overbreak and underbreak control of periphery holes shaped blasting around tunnels

Abstract Traditional blasting methods face challenges such as disturbance to the surrounding rock, overbreak and underbreak. This paper studies the rock damage and optimizes the overbreak and underbreak control in tunnel periphery blasting using shaped charge blasting. It adopts both the LS-DYNA numerical simulation method and the field blasting test to analyse the blasting of shaped charge and circular charge in semi-periphery holes. It also compares the differences in the propagation speed of the explosive stress wave, the surrounding rock damage, and the overbreak between directional shaped charge blasting and traditional blasting. The results indicate that there is no significant difference in the propagation speed of explosive stress waves between circular charge and shaped charge in the surrounding rock. The stress wave propagates faster between nearby periphery holes than it does from the periphery holes to the smooth blasting layer’s free boundary. Their speeds are 6500 m s −1 and 5500 m s −1 , respectively. Shaped charge directs less energy perpendicular to the energy concentration direction. Shaped charge focuses on the blasting energy along the designed contour line, resulting in a high energy efficiency. Shaped charge blasting reduces the overbreak area by 23.8%, compared with circular charge blasting. In the field tests, the percentage of overbreak depths above 30 cm is 20% lower than using conventional circular charge blasting. The average linear overbreak depth has decreased by 47%, and the maximum linear overbreak depth is reduced by 56%.