Study on Flow Field Evolution Law of Goaf in Fully Mechanized Caving Face and Gel Air Leakage Blocking Technology under Withdrawal Condition

During the retreat period of the fully mechanized coal mining face underground, the intensity of air leakage is high and the distribution of residual coal is widespread, which exacerbate the risk of spontaneous combustion of residual coal in the goaf: particle flow code (PFC) and computational fluid dynamics (CFD). The results showed that during the retreat period of the working face, the collapse of the goaf roof gradually stabilized and the "O" ring reached its maximum range. The porosity distribution was between 0.611 and 0.625, which first decreased and then increased with the depth of the goaf, showing a "bowl"-shaped distribution. Connected fracture development zones are formed around the goaf. The intensity of air leakage on both sides of the goaf is relatively high, with air leakage speeds ranging from 0.25 to 0.3 m/s. As the inlet air speed decreases, the range of airflow diffusion in the goaf also decreases. After the flexible composite net and gel measures are taken, the maximum air leakage velocity is 0.07 m/s, about 1/3 of that when no measures are taken, the widest air leakage range in the goaf is reduced to 23 m, the CO in the upper corner of the working face is gradually reduced from 16 to 0 ppm, and the temperature is reduced from 33.9 to 28.5 °C. The research results have important guiding significance for the fire prevention and extinguishing work during the retreat period of the working face.