Research on the evolution mechanism of the topological relationship of the property parameters of the mining overburden rock pressure relief gas migration channel

Many factors combine to influence the spatial distribution characteristics of overburden fracture during the increasingly intense mining process in coal mines. The characteristics of overburden fracture distribution has important significance in guiding the gas management in liberated layer mining. Several sets of two-dimensional physical similarity simulation experiments were carried out to investigated the distribution characteristics of overburden fracture network and the property parameters of the pressure relief gas storage and migration channels under different mining conditions (mining height, advancement speed, key layer upon layer and coal seam inclination). The topological network with geometric and fissure parameters was obtained. The topological transformation of the real stem system was simplified based on the theory of complex network evolution, and the evolution characteristics of the stem system structure and factor nodes of the transportation and storage channel was analyzed combined with the complex network characteristic parameters. The influencing factors of the overburden fissure network stem system was quantitatively described, and a matrix and model of the network structure of pressure relief gas transport and storage channel were established. The results indicated that, the development range, through degree, and fractal dimension of pressure relief gas migration and storge channel expand with the increase of mining height, key layer position, and coal seam dip angle. However, the development range shown a decreasing trend with the acceleration of advancing speed. The increase in mining height had the greatest impact on the amount of separation, with a 146.9% increase at 6 m mining height compared to 4 m. The variation in fracture density was mainly influenced by the dip angle of the coal seam, and was less influenced by the advancing speed. Arranging the boreholes in high-density areas (density > 4.7 pieces/m) can effectively act as a gas retention. The research results can further optimize the arrangement parameters of gas extraction boreholes under the influence of different factors, improve the efficiency of gas extraction, so as to ensure the safe and efficient recovery of the working face, which is of certain practical significance for the realization of accurate and green gas extraction.