Periodic Fracture Model and Control of Hard Roof of Thin Coal Seam Short-wall Face: A Case Study of Zhuzhuang Coal Mine

Abstract

The periodic fracture of the hard roof above the working face is the key influencing factor of ground pressure management in the underground exploitation of coal mines. A reasonable breaking span is greatly significant to ensure safe and efficient exploitation of coal mines. The hard roof of the short-wall working face is difficult to break during the mining process. Hence, the II646 fully mechanized coalface of the Zhuzhuang Coal Mine in a mining area in Huaibei, China was taken as the engineering background. Based on the theory of elasticity mechanics, an elastic thin-plate mechanical model of short-wall working faces was established, with the condition of two opposite edges simply supported and with one edge clamped and the other edge free (SCSF). The fracture law of hard roof was studied via theoretical analysis and onsite monitoring. Results show that the breaking span of the hard roof of the II646 working face is 80-90 m. The calculation results of the thin plate mechanical model are closer to the actual situation on-site than the calculation results of the traditional cantilever beam model. By performing calculations with maximum tensile stress theory and a bearing load capacity, the reasonable breaking span was 35 m. Based on the results of the theoretical analysis, the roof weakening scheme of the long-hole pre-splitting blasting was proposed for the II646 working face. The field practice results show that, after using deep-hole pre-splitting blasting, the periodic weighting interval and the working resistance of the support are approximately 35 m and less than 40.1 MPa, respectively. Both of these numbers indicate a decrease compared with before the roof weakens, which the periodic weighting interval (90 m) and working resistance of support (greater than 40.1 MPa), thus avoiding support collapse accidents and achieving safe and efficient mining of the short-wall working face. Such results can provide a scientific basis for the hard roof treatment of short-wall, fully mechanized working faces under similar conditions.