Studies show that accurate division of spontaneous combustion (SC) zones in the goaf and the determination of the prediction system of the SC index are of great significance to prevent spontaneous and unwanted combustions in the goaf. Aiming at resolving the problem of coal SC in the goaf of an “isolated-island” fully mechanized caving face, a multiphysics model coupled with gas flow field and gas concentration field was established in the present study. Taking the 8824 working face of Nanzhuang coal mine as the research object and the oxygen concentration as the division index, coal SC was simulated in the goaf. The obtained results show that the ranges of heat dissipation zone, oxidation zone, and the asphyxia zone on the air inlet side are around 0–107 m, 107–239 m, and beyond 239 m, respectively. Moreover, the ranges of the three zones on the return air side are 0–13 m, 13–189 m, and beyond 189 m, respectively. The ranges of the three zones in the middle of goaf are 0–52 m, 52–213 m, and beyond 213 m, respectively. The performed analyses demonstrate that the obtained simulation results are consistent with the experimental data. Meanwhile, the coal programmed temperature rise experiment was carried out to improve the prediction index gas system of SC. It was found that CO and C₂H₄ can be used as early warning indices of SC in the goaf, while C₂H₆, C₃H₈, and C₂H₄/C₂H₆ are auxiliary indices to master the coal SC.

This research aims to investigate the impact of high-pressure water jet cutting parameters on pressure alleviation around the coal slot. A numerical model of high-pressure water jet cutting coal was developed using FLAC^3D software, allowing for a detailed study of how each cutting parameter affects the pressure relief effect of the slot. The key findings are as follows: as the water jet pressure increases, the plastic area of the coal body around the kerf expands, although the rate of increase diminishes, with the optimal water jet pressure being 30 Mpa. The results suggest that hydraulic slotting measures are particularly beneficial for outburst prevention in high in situ stress coal seams. The pressure relief range exponentially grows with an increase in the kerf depth, signifying that enhancing the kerf depth has a notable effect on improving the hydraulic kerf pressure relief. As the slit width increases, the volume of the slit enlarges, leading to a significant rise in the pressure relief range of the surrounding coal body. Given that an increase in the slit width necessitates an increase in the nozzle outlet diameter and slotting time, the optimal slit width is determined to be 0.2 m. The research concludes that the optimal hydraulic slit spacing is 3 m. This study offers valuable theoretical guidance for high-pressure water jet slotting.

When stratified mining is used in extrathick coal seam, the gas emission in goaf of the first mining face is large, and it is easy to cause gas overrun in the upper corner during the rapid advance of the working face, which seriously affects the safe and efficient mining of the working face. The gas drainage in goaf by roof high-drainage way is the fundamental solution to solve the gas overrun in the upper corner, and the reasonable layout position is related to the drainage effect of high-drainage way. In this paper, 206 slicing mining face of Tingnan Coal Mine in Binchang Mining Area of Shaanxi Province is taken as an engineering example. Theoretical analysis, fluent numerical simulation, and field verification are used to study and analyze the reasonable layout position and drainage effect of roof high-drainage way in working face. The research results show that the reasonable position of the high-drainage way layout is the horizontal distance of 15m, the vertical distance of 21m and 26m, the horizontal distance of 25m, and the vertical distance of 21m and 26m. In the layout position of 15m horizontal and 21m vertical, the gas drainage volume of high-drainage roadway is 16.423.3m³/min, and the average gas drainage volume is 20.45m³/min. The gas drainage volume of high-drainage roadway accounts for 52.1 of the gas emission, which achieves the expected effect and realizes the safety requirements of gas prevention and control in working face. The research results of this paper can provide guidance for the layout of high-drainage way in Tingnan Coal Mine and adjacent mines.

Urban underground engineering is generally buried at a shallow depth and suffers long-term environmental water effects such as rainfall, rivers, underground pipeline leakage, and groundwater. The mechanical properties of the structures are affected by constant deterioration, which seriously hinders the safe, healthy, and sustainable development of the city. On the basis of on-site investigation of civil defense engineering, this article simulates the water environment conditions of mortar in underground engineering in the laboratory and conducts manual sample preparation in the laboratory. Then, water, H₂CO₃, NaCl, and Na₂CO₃ solution or wet–dry cycles are used to corrode the sample, respectively. A uniaxial compression test, Brazilian splitting test, analyses of the acoustic emission signals and electromagnetic signals, and magnetic imaging testing are performed, respectively. The results show that an increase in the action time of environmental water leads to a gradual increase in the uniaxial compressive strength, tensile strength, and elastic modulus of cement mortar, but it will decrease over a long period of time. Different environmental water components can also lead to a different performance of soaked mortar. The uniaxial compressive strength R, tensile strength σ_t, and elastic modulus E of mortar samples exhibit values in different solutions in the order of H₂CO₃ solution < NaCl solution < Na₂CO₃ solution < water. A moderate solution soak time can enhance the mechanical properties of the mortar, but this effect decreases at long time scales. The effect of wet–dry cycles on the mechanical properties and degradation process of mortar is significant. With the increase in wet–dry cycles, the porosity of mortar continuously increases. The cumulative ringing count, energy, amplitude, and impact number of acoustic emission signals always increase when the samples are loaded to failure. The uniaxial compressive strength, tensile strength, and elastic modulus first increase and then decrease. The experimental results lay the foundation for further investigating the performance changes in mortar under complex water environments in underground engineering.