Experimental study on crack propagation of slit charge blasting in media with vertical bedding plane

Abstract

The joints have significant effects on crack propagation in slit charge blasting. In this paper,the caustic method is adopted to study the law of crack propagation in vertical jointed media under slit charge blasting. The results show that compared with the intact media without joint,in single slit charge blasting the velocity of induced dynamic crack is lower in the media with vertical joint,and the crack length on one side of the borehole decreases by about 15.5%. The reflected wave,generated by the reflection of stress wave at the vertical joint,increases the stress intensity factor of the opposite propagated crack,which leads to suppressing the forward propagation of dynamic crack. The closer the distance between the hole and the joint,the stronger the suppressing effect KⅡd,whereas decreases the KⅠd of the joint on crack propagation. Under double slit charge blasting with simultaneous initiation,the explosion stress wave,generated by the adjacent borehole,has a positive effect on the crack propagation with opposite directions,which makes both the dynamic stress intensity factor and crack velocity increase significantly,leads the dynamic passing through the vertical joints directly without deflection,improes the directional propagation ability of dynamic crack in jointed rock,and the length of crack increasesby more than 50% compared with the single slit charge blasting. The results provide a theoretical basis for carrying out directional fracture blasting with slit charge in jointed rock mass.

Keywords

• layered media
• slit charge
• caustic experiment
• crack propagation
• stress intensity factor