Spatial distribution characteristics of pressure-relief gas and precision, efficient drainage in mining stope

The spatial patterns of gases released for pressure relief are investigated to guide the accurate and efficient extraction of such gases within the mining working face. The work focused on a coal mining face in Inner Mongolia, specifically the 42,205 fully-mechanized mining face. The purpose was to analyze the spatial distribution patterns of pressure-relief gases in both the 42,205 fully-mechanized coal mining working face and the goaf by measuring gas concentration at the mining face and simulating gas migration. A well-organized gas drainage system was implemented based on the distribution characteristics of gases to ensure the accurate and efficient drainage of pressure-relief gases during mining. Certain patterns were observed in gas concentration distribution on the mining face according to the 3D grid method and inverse distance interpolation. Spatially, higher locations on the measurement planes exhibited smaller low gas concentration areas compared to lower locations on the same planes. Both the maximum and minimum gas concentration was located on the goaf's sides on a single measurement plane. Gas concentration behind hydraulic support was significantly higher than that in front of hydraulic support. The horizontal distribution of porosity and permeability demonstrated a concave pattern in the porous media of the goaf. Goaf's sides, especially near the tunnels, had higher porosity and permeability, while the central region had lower values. A noticeable decline existed in both porosity and permeability with the increased distance from floor in the vertical direction. The gas volume fraction was relatively small but with a steep gradient in the shallow part of the goaf. There was a gradual reduction in the gradient of the gas volume fraction as the goaf extended deeper, while its numerical value stabilized after increasing. Gas levels in the upper corner of the 42205 mining face consistently ranged from 0.13 to 0.94% through the monitoring and analysis of continuous on-site gas drainage. Gas concentration ranged from 0.21 to 0.86% in the return airway, and they varied from 0.22 to 0.92% in the mining face. The maximum gas concentration was consistently below 1%, remaining within the safety range and meeting the safety standards outlined in the Coal Mine Safety Regulations. This confirmed the rationality and effectiveness of the arrangement and parameters of the gas drainage system for effective drainage. The results can be applied to engineering and technical personnel and guide the gas control in fully mechanized coal mining faces.