Technology of pressure relief and permeability enhancement with high pressure air blasting under high geo-stress

To explore the unconventional technology for pressure relief and permeability enhancement under high geo- stress,the mechanism of pressure relief is studied by high pressure air blasting in deep mine. The difference of coal failure caused by air blasting between surface and underground is analyzed. The theoretical calculation model with pressure relief range of high pressure air blasting based on high geo-stress is established. Taking the Dingji Mine as an engineering example,the authors calculate the damage range of air blasting using the theoretical model. The technology and equipment of high pressure air blasting for pressure relief and permeability enhancement is introduced. The ground experiments of high pressure air blasting are carried out,and the damage effects and characteristics of concrete specimens are obtained with and without displacement constraints. The effect of compression wave induced by air blasting reflection on sample damage is analyzed. Based on the underground field tests,the effect of air blasting for pressure re- lief and permeability enhancement is studied. The transformation characteristics of gas flow,gas extraction,gas attenua- tion coefficient and permeability coefficient are analyzed before and after air blasting. Combined theoretical calculation and experience,the optimal range for pressure relief and permeability enhancement is obtained after air blasting. The results show that the damage extent of concrete samples with and without displacement constraints is remarkable and presents radial fracture characteristics under the nearly 60 MPa air pressure. In the Dingji Coal Mine of Huainan,the gas flow after air blasting is 6-8 times of that with non-air blasting,the gas extraction is 4-7 times of that before air blasting,the permeability coefficient is 5-1 050 times of that with non-air blasting,the attenuation coefficient is 0. 4 times of that with non-air blasting,and the optimal pressure relief radius is no more than 2 m. The first air blasting weakens the mechanical properties of coal around the blasting hole,which is equivalent to the unloading effect around the blasting hole. Under the combined action of secondary air blasting and high geo-stress,a large range of loosening damage is formed,thus achieving the purpose of pressure relief and permeability enhancement.