Advancement Area Control Technology for High Mine Pressure Dynamic Disasters in Thick and Hard Roofs

Abstract

Abstract The western mining area exhibits the superimposed development of a thick and hard roof under the continental sedimentation of multiple ancient rivers. In this case, the fully mechanized caving working face with a large mining height has a high stope pressure, which induces rock burst, mine earthquake, and hurricane in the goaf. To determine the fracture evolution characteristics of overlying strata in a fully mechanized caving mining with a large mining hard roof height, this study investigated the disaster mechanism of hard roof strata that undergo a large “cantilever beam” collapse and produce fracture impact energy. The study was based on the cantilever beam fracture theory, and the UDEC discrete element numerical simulation was used. According to the concept of partition weakening control of a hard roof, an advance weakening technology for staged fracturing of a hard roof was proposed, a mechanical model for a reasonable hanging length of a hard roof was established, and a quantitative formula for determining a reasonable hanging length of a hard roof was developed. Fracturing models under different crustal stress conditions were analyzed, including the ellipsoid fracture network perpendicular to the direction of the working face, the horizontal fracture surface network perpendicular to the direction of the working face, and the near-linear fracture surface dominated by vertical fractures. The first and second models were effective governance models for hard roof disasters. The test was performed in a typical working face, and the results showed that the average periodic weighting step of the roof after fracturing weakening decreased from 18.7 m to 8.6 m, and the weighting strength decreased by 21.67%. These results indicate effective prevention and control of high-mining-pressure disasters in a thick and hard roof. The thick and hard roof was transformed into multiple small blocks by using open-hole staged hydraulic fracturing, resulting in significantly reduced accumulated energy and energy loss during fracturing. In this way, the partition and segmented controllable fracturing length collapse of the thick and hard roof was realized, facilitating the transfer and dissipation of the roof stress as well as the effective control of dynamic disasters. Under the fracturing effect, the caving pattern and breaking degree of the near-field, low-level thick and hard roof were effectively changed, resulting in an improved scope of the working face caving zone and increased gangue filling degree in the goaf. Hence, effective suppression of the far-field strata subsidence and surface subsidence was achieved. This study provides a technical model support for the synergistic control of high-mining-pressure dynamic disasters, mine earthquakes, and surface subsidence in hard roofs.