High rate of dust generation and serious dust diffusion in dry directional drilling in soft and broken coal seams (SBCS) have long been critical problems in the mining process. To solve these problems, in this study, a dust hood was designed and applied to realize non-contact dust control in drilling holes. The optimal performance of the dust hood was achieved when different technical parameters, including the gap width between the dust hood and the drill pipe, the air-slot width of the sealing device, the slag discharge pressure, and the air curtain pressure were controlled at 2 mm, 0.2 mm, 0.3 MPa, and 0.5 MPa, respectively. As a result, the dust concentration was reduced from 540 mg/m³ to 15 mg/m³, with dust control efficiency reaching 97.2%. The in situ test results confirmed good dust control effects, as the dust control efficiency reached 98.3% after using the dust hood.

As the laws of structure deformation and structural stress variation under freezing construction around high-rise buildings are not clear and no engineering experience can be referred to, freezing method construction in this situation is paired with huge safety risks. In this paper, freezing construction was successfully carried out around the main shaft tower in Chensilou Coal Mine by taking the following protective measures: symmetrical drilling, local freezing and hot water circulation. The elevation of the shaft tower foundation is continuously measured during the process of drilling, frost heaving and thaw settlement (hereinafter referred to as the DHS process). Benefiting from these protective measures, the maximum inclination value (−0.406 mm/m) of the shaft tower is controlled at well below the allowable value. The observation data informed the settlement and inclination of the tower foundation during the DHS process. A numerical model of the shaft tower is further established based on the observation data to reveal the tower structure’s law of stress variation during the DHS process. In addition, the fitting equation between the tower inclination value and the structural stress is obtained, which can provide a reference for freezing construction of similar high-rise buildings.

Protective layer mining is an effective measure for addressing gas-related hazards. After the extraction of the protective layer, the stress redistribution and evolution in the overlying coal and rock masses exert a significant influence on gas migration and pressure-relief storage within the goaf. Therefore, to gain a deeper understanding of the evolution of strike- and incline-direction stresses during protective layer mining, this study investigates the stress distribution characteristics and laws throughout the lower protective seam extraction process. Based on the geological and mining conditions of the 864 working face in a mine located in Huaibei, a numerical model was established using FLAC3D to analyze the evolution of coal body stress along both strike- and incline-direction after protective layer mining. The simulation results indicate that the stress-relief zone in the X-direction is mainly distributed around the coal seam areas corresponding to the haulage and ventilation roadways, while the stress-relief zone in the Y-direction is primarily located near the crosscut and set-up room, as well as ahead of the working face. After mining the protective layer, the protected seam exhibits a stress evolution pattern characterized by increasing vertical stress and decreasing horizontal stress.

Background: The pressure reduction range in traditional protective coal mining is often set conservatively, resulting in diminished actual pressure reduction effects near the mining boundary. Therefore, analyzing the stress and permeability evolution patterns at the mining boundary is particularly essential. Method: A three-dimensional numerical model was established according to the mining conditions of the 864 working face in T Mine to study the stress evolution, fissure development, and permeability evolution of the coal and rock mass overlying the protective seam mining, especially those near the mining boundary. Results: The overlying coal and surrounding rock mass near the mining boundary are in the state of increasing vertical stress and decreasing horizontal stress, and under this mechanical path of “increasing axial pressure and decreasing peripheral pressure”, the coal mass is damaged and destroyed, fissures are developed, and the permeability is increased; as a result, the coal and surrounding rock mass near the mining boundary mainly produce vertical longitudinal fissures, and the permeability can be increased 900 times compared with that of the overlying coal and surrounding rock mass in the mining boundary. After ground drilling and enhanced depressurization, the measured maximum gas content of the coal mass at the strike boundary is 3.25 m³/t, and the measured maximum gas content of the coal mass at the inclination boundary is 2.63 m³/t. Conclusions: After mining the protective layer, the permeability enhancement effect diminishes from the center toward the sides, yet remains sufficient to eliminate the risk of gas outbursts. This validates the importance of verifying permeability enhancement effects at coal seam boundaries.