In comparison to traditional longwall mining, "roof-cutting and pressure-releasing" mining along gob-side entry retaining changes the permeability of the gob, as well as the pressure-relief characteristics and caving mode of the overlying strata. These changes are a result of the interaction of these factors, which also changes the boundary condition of the gob and the airflow movement law of the working face and the gob. In order to study the law of air flow movement in the working face and gob under the "roof-cutting and pressure-releasing" mining along gob-side entry retaining, the permeability model of gob was established under the engineering background of the 21,304 experimental working face of Chengjiao coal mine, then using fluent numerical simulation software, the movement law of air flow in working face and gob is simulated. The results show that the law of air leakage is much different from that of traditional longwall mining, and there are two main air leakage routes, First, most of the airflow will flow directly into the gob-side entry retaining under the action of inertia, and it will collide with the air flow provided by the fan at the end of the gob-side entry retaining, and the air will leak in the gob along the airflow direction; second, when the remaining airflow flows to the working face, the air leakage is serious in the air inlet corner, and most of the air flow flows into the gob. In view of the air leakage area, the air leakage prevention measures are put forward, such as setting the baffle plate, hanging the wind shield at the corner, and blocking the wall of the roadway with guniting; the simulation results show that the air leakage area is obviously reduced, and it is consistent with the measured data. The simulation results can generally describe the law of air flow movement in the face and gob with "roof-cutting and pressure-releasing".

In coal mine goafs, spontaneous combustion of coal can result in methane accumulation, which raises the danger of methane explosion disasters. As an atmospheric control tool, ventilation is applied to ensure air quality for avoiding disasters in underground mines. However, during the process of the spontaneous combustion of coal in coal mine goafs, the impact of ventilation dilution on the possible methane explosions induced by coal combustion has not been well investigated. In this study, a validated gas flow model for the spontaneous coal combustion environment in goafs of coal mines is adopted to investigate the influence of ventilation dilution at the three stages of the spontaneous combustion of coal. The research conclusions suggest that (1) ventilation dilution is a quick measure to dilute methane concentration and intensify heat transfer in the vertical direction in coal mine goafs; (2) ventilation dilution can lessen the danger of methane explosions by diluting methane concentration to the lower explosive limit for methane when coal combustion takes place on the air-inlet side; (3) however, ventilation dilution increases the methane explosion risk by decreasing methane concentration, resulting in explosive methane limits, if coal combustion occurs on the air-return side. This provides a reference for the management of ventilation during a spontaneous coal combustion disaster in the goafs of coal mines with methane.

Coal permeability is related to the fracture-pore structure of coal and is a key factor in determining gas drainage efficiency. The characteristics of the methane flow in coal fractures are different from those in coal matrix pores. However, due to the difficulty of observing fast methane flow in coal fractures, the effect of gas flow in coal fractures on coal permeability has seldom been considered and investigated. In this study, a cylindrical coal sample is used for the measurement of coal permeability under different gas pressures, and an abrupt change in coal permeability evolution was observed. Then, a tandem fracture-pore permeability model was adopted to analyze these new methane flow phenomena. In this permeability model, the deformation of coal fractures was directly analyzed and modeled without the reversed derivation. With the consideration of elastic modulus of coal fractures, the deformation of coal fractures is controlled by the effective strain of coal fractures, the adsorption-induced strain and effective strain of coal matrix. The research results show that (1) coal fractures quickly and significantly influence coal permeability by resisting coal deformation; (2) a complete evolution of coal permeability consists of the fast permeability change caused by methane flow in coal fractures and the slow permeability change caused by methane flow in coal matrix; (3) the low efficiency of gas mass exchange between coal fractures and coal matrix leads to a two-stage evolution for gas desorption flow and coal permeability.

To improve coal recovery and mitigate high-stress hazards in deep mining, the roof cutting and pressure relief mining (abbreviated as “RCPR”) without coal pillars has been widely implemented in Chinese coal mines. This study combines physical similarity experiments with numerical simulation to examine, before and after extraction, how roof cutting alters pressure-relief behavior and stress migration at key locations of the panel, and to formulate a mathematical model of roof-cutting-induced stress migration. Results show that roof cutting reshapes the caving structure of the overburden and improves the stress environment in critical zones. Two dominant migration paths are identified: (i) horizontal transfer from the roadway roof toward the deep coal-pillar zone and the goaf edge, and (ii) vertical transfer from lower to higher roof levels. Consequently, the surrounding rock near the roadway experiences a “dilution-weakening” effect at low levels, while middle–upper levels exhibit a “migration-storage” response. Roof cutting also narrows the stress-recovery zone at the goaf margin, enhances load-bearing of the compacted caving zone, and drives stress toward the pillar interior and goaf edge. Enforcing stress conservation, a dual-side stress-migration model (pillar side and goaf side) is established, introducing a stress-migration ratio to quantify the directionality and intensity of stress transfer. These findings refine the theoretical framework of “RCPR” mining.