Research and application of empty hole effect under blasting loading

The characteristics of deep hole blasting are effective and safe in deep underground rock breaking. To im- prove the blasting effect and decrease the integrity of rock mass,an empty hole was used to control the crack growth and supply rock displacement. The range of blasting zone,such as crush zone,fracture zone and elastic zone,was deter- mined according to the blasting theory. The fracture direction was investigated through experiment when the empty hole situated in different zones. The influence of distance between charging hole and empty hole on crack extension was an- alyzed by experiment. The strain around the empty hole was measured at different conditions. The results show that when the empty hole is located at fracture zone,the empty hole is able to control the direction of crack growth effec- tively. It plays a role in directional fracture,and the strain reaches maximum in this situation. In the application of coal mine roof weakening in Huaibei Mining Group,the difficult-caving roof was changed into easy-caving roof,which was attributed to the reasonable arrangement of blasting parameters. After blasting,the rock acoustic velocity was reduced by 40% -50% ,and the cracks were extended in the blasting area. The resistance of the working face was less than that before. The blasting result is in line with the design requirements and the production efficiency is improved.