Dynamic disaster evolution mechanism of high mine pressure at hard roof and advance area prevention and control technology

The overlying roof on the hard roof working bench is usually not likely to fall off, while tends to form dynamic pressure disaster. The stress evolution characteristics and roof breaking mechanism before and after hard roof weakening were analyzed and revealed using the methods of numerical simulation and theoretical analysis, and the advance area prevention and control technology were proposed and applied in the field practice, for the typical dynamic disaster problem of high mine pressure that was caused by the hard roof against the background of the Buertai Coal Mine in the Shendong Mine Area. As indicated by the results, there were three stages of the hard roof breaking evolution characteristics, i.e. the “long cantilever” stage — “masonry beam falling and destabilization” stage — re-compaction stage. At the “long cantilever” stage, which was also the main stage of weakening modification and control, the roof stress at the upper support was increased significantly to 6.8 MPa; the roof stress at the upper support before breaking was twice of that after breaking; the stress relief resulted from the critical breaking was the root cause of the high mine pressure. On the basis of the occurrence mechanism analysis of the hard roof disaster, the advance area prevention and control technology of "wide-range large space" was proposed, and the green, accurate and wide-range prevention and control advantages, the key technologies of drilling trajectory control, hole plugging quality control and multi-hole linkage effects as well as the governing evaluation system were elaborated. The reliability of the prevention and control technologies were verified in combination of the numerical simulation. After the "long cantilever" structure weakening, the roof stress at the upper support before breaking was 4.6 MPa, with the drop rate of 32.4%. The three stages of the roof breaking evolution characteristics were pre-weighting stage — “masonry beam falling and destabilization” stage — re-compaction stage. After weakening, the drop rate of the roof stress at the upper support for each stage was 32.4%–79.4%, which indicated that the preformed fissure weak surface and the hard stratum integrity reduction can effectively change the roof breaking structure and significantly decrease the weighting intensity. As indicated by the practice, the pressure drop occurred several times during fracturing, the drop rate was over 3 MPa, and the detection fracture developed to more than 30 m; the drop rate of the periodic weighting interval of the working bench before and after fracturing was 44.9%, and the drop rate of the support weighting load was 18.1%. The governing effect was good. The study result can provide references for the dynamic disaster governing in the similar mine areas.