Study on the air permeability characteristics of coal gangue dump slope gangue particles

The phenomenon of particle segregation in the gangue aggregate on the slope surface of the coal gangue mountain significantly influences its permeability characteristics. To investigate the air infiltration characteristics of the slope surface, a self-designed indoor permeability measurement device was utilized. By integrating the theories of granular soil mechanics, ventilation, and FLUENT numerical simulation, the overall distribution patterns of porosity and permeability of the gangue aggregate at different heights and depths on the coal gangue slope surface were studied, as well as the characteristics of air infiltration and temperature distribution. These findings were validated through on-site measurements. The results demonstrate that the distribution characteristics of porosity and permeability in the shallow part of the gangue slope surface are significantly affected by the particle segregation phenomenon, exhibiting a nonlinear negative exponential decay pattern as the height and depth increase. As the particle size of the slope surface gangue aggregate increases, its porosity also shows an increasing trend, but the rate of increase gradually slows down. The presence of a loess layer covering the top of the gangue slope hinders fluid flow and results in lower oxygen content, which is unfavorable for exothermic oxidation reactions. Moreover, at the bottom, where the porosity is larger, the wind speed is excessively high, creating unfavorable heat accumulation conditions. Therefore, the high-temperature region is located in the upper part of the gangue slope, 2～3 meters away from the slope surface, reaching temperatures as high as 780 K. Under the combined influence of thermal wind pressure and external wind pressure, the highest wind speed is found in the upper-middle part near the slope surface, reaching up to 0.06 m/s. Furthermore, as we delve deeper into the gangue slope in the X and Z directions, the flow velocity and the rate of decrease in oxygen concentration gradually decrease. Overall, the distribution of porosity on the gangue slope surface is a crucial factor affecting the air infiltration characteristics within the coal gangue mountain. Through the study of wind speed, oxygen concentration, and temperature fields in the gangue slope, this paper roughly categorizes the gangue slope into a surface cooling zone, a heat-gathering flammable zone, and an internal low-temperature zone. The findings from this research can serve as a fundamental reference for accurately predicting and identifying self-ignition fire zones in the arid and windy mining regions of central and western China.