Investigation On Protection Range In Exploiting The Steep Lower-protective Layer With A Bow Pseudo-incline Technique

As the mining depth increased in the mine, coal and gas outburst prone mine manifolded, mining protection seam became an important safe measure in local prevention and control when mining crop out seam group.Aimed at the existed problems to demarcation of protection scope of nether protective seam in exploiting steeply inclined seam. With the background of nether protective seam in exploiting steeply inclined seam in 3-1 Dong-Lin mining.Combining with theory analysis, on-site research and numerical simulation, studied the methods of demarcating protection scope of nether protective seam in exploiting steeply inclined seam mining.1) Analyzed the feasibility of selecting nether protective seam mining from 3-1 Dong-Lin mining.2) Identified the coal and rock deformation patterns of activity in Dong-lin coal mine while exploiting steeply inclined seam with under-protective Seam. Ambient moving rock formed"vertical three straps"and"horizontal three straps"; at the same time, the stress of the above rock has changed because of exploiting nether protective seam, the pressure has centralized near incision and working face, while the pressure has realized corresponding hollow area after exploitation.3) Many holes were lie to observe the transformation of pressure and flux in the protective layer (K4) opposite the protecting layer (K6) while pushing working face. Analyzing the data, the"Four-zone"range of the gas pressure and the"M"range of the gas flux along with the mining down-protective layer were studied. Based on the transition of the gas pressure, the inclined protective layer has a pressure relief angle of 86°; while based on the transition of the gas pressure and the gas flux, the protective angle along the oblique working face of the protective layer is 45°～72.47°.4) Through making use of 3D-software to simulate exploiting nether protective seam, observing changing process of stress field and deformation field of protected layer, the rule is defined that the pressure and strain of protected layer is changing as the working face is pushing. Based on the protection rule of the deformation and stress pressure-relief of protective layer mining, the inclined protected scope of protective layer K6 was demarcated,the up and down pressure-relief angles along inclined of steep-dipping lower protective layer is 82°～84.9°, the pressure-relief angle along the level of nether protective layer is anomaly, the range is 48.9°～73.6°; the pressure-relief angle corresponding hollow area after exploitation is the biggest, which is 73.6°; the down one is smaller, which is 54°; and the up is 48.9°.5) By contrast with spot and numerical simulation results, after steeply inclined and pitching oblique lower protective seam (K6)in steeply inclined, the relative error of the lower protective pressure-relief angle of protected seam (K4 ) by incline between the two methods was 1.3%, and in strike was 1.6%~7.9%. This indicated that it was reliability to simulate mining pitching oblique lower protective seam by numerical analysis method.The demarcation of nether protective seam in Dong-Lin mine can operate the disposal of the protected working face K4 in exploiting nether protective seam K6.