Determination of the Height of the Water-Conducting Fractured Zone in Difficult Geological Structures: A Case Study in Zhao Gu No. 1 Coal Seam

The method for determining the upper limit for safe mining with regard to water and sand collapse prevention under thick alluvium and thin bedrock layers is a critical parameter for ensuring the sustainable development of a mine. The height of the water-conducting fractured zone (HWCFZ) is an important index parameter in the prediction and prevention of water and sand collapse. This research was conducted based on the concrete geological condition of the Zhao Gu No. 1 coal mine. First, a field measurement method was used to observe the HWCFZ of a mined panel. The discrete element method was applied to establish a corresponding model, which was calibrated using the measurement data. Then, calculation models for different bedrock thicknesses were developed to analyze the evolution law of the water-conducting fractured zone at different bedrock thicknesses and mining heights. The safe mining upper limits for different bedrock thicknesses were obtained. The relationships between the developing HWCFZ and bedrock thickness/mining height were determined. Using the research results as the main indices, an industrial experiment was performed on the 11,191 panel. The partition limit mining height was implemented in the panel, and safe production was realized. On the basis of the research results, 40,199,336.3 t of coal resources were successfully released, increasing the resource recovery rate by 31.72% and extending the mine service life by 12.5 years. This study not only provided technical support for the sustainable development of the Zhao Gu No. 1 coal seam, but could also be used for safe and highly efficient mining in other coal mines under similar geological conditions.