Pressure Relief by Blasting Roof Cutting in Close Seam Group Mining under Thick Sandstone to Enhance Gas Extraction for Mining Safety

Abstract

Close seam group mining under thin immediate roofs and thick sandstone walls is typically performed with a strong mine pressure and gas concentration, which pose considerable risks to miners. In this study, the mechanism of pressure relief and permeability enhancement to enhance gas extraction for mining safety through blasting roof cutting were investigated through theoretical analyses, numerical simulations, and laboratory tests. The results revealed that, near the blast-hole, which produced numerous cracks, blasting disturbed the integrity of the thick-layer roofs and redistributed the stress near the blast-hole, which prevented violent mine pressure caused by excessive fracture distances on the thick and hard roofs, reduced the additional load on the support, increased vertical gas migration, and ameliorated the effect of gas drainage caused by high-level boreholes. The field applications of forced roof cutting through deep-hole blasting in the II 7224N face of the Renlou coal mine (Huaibei, Anhui, PR China) demonstrated that the occurrence of excessive pressure on the fully mechanized mining hydraulic support was prevented. The gas extraction volume of high-level boreholes was maintained at 6–8 m3/min; the extraction concentration was stable at approximately 35%; and the gas concentration in the upper corner of the coal face was lessened from 7% to <1%, which ensured normal mining in the coal face. The current results can provide data reference and a theoretical basis for roof management and gas control of the same type of coal face.