Spontaneous combustion of coal is one of the major hazards threatening production safety during longwall mining. Mining-induced voids, which provide passages for air leakage, are the key factor triggering spontaneous combustion of coal in longwall goafs. In this study, a comprehensive method, which combined pressure balance, grouting injection, and filling fissures, was proposed to prevent spontaneous combustion of coal in longwall goafs with complex air leakage. Field engineering practice was carried out in Sitai Coal Mine in China. The results demonstrated that with the application of the proposed method, in the working face, the concentration of CO was decreased from 31ppm to 0 and the air leakage quantity was decreased from 261 to below 80 m³min^-1. The gas samples analysis from the gob areas also indicated that concentrations of O₂ and CO were successively decreased, indicating that the risk of spontaneous combustion of coal in goafs was eliminated. The above mentioned analysis indicates that, the method proposed in this study is useful and efficient. Successful application of this technology could provide reference for the treatment of other coal mines.

It is well known that underground in situ pyrolysis technology for oil shale production is a promising field. In the in situ modification mining process, the permeability property of a shale matrix has a great effect on the transport capacity of pyrolytic products. For oil shale undergoing pyrolysis, the changes of internal structure (fracture and pore space) have a considerable influence on the permeability network which further affects the migration of hydrocarbon products. In this study, based on an oil shale retorting experiment performed under different temperatures (20 °C, 100 °C, 200 °C, 300 °C, 325 °C, 350 °C, 375 °C, 400 °C, 425 °C, 450 °C, 475 °C, 500 °C, 525 °C, 550 °C, 575 °C, 600 °C), an investigation on the distribution characteristics of the fractures was conducted using micro-CT technology. Meanwhile, mercury injection porosimetry was used to characterize the pore structure of the oil shale samples under different temperatures. Finally, a fracture-pore dual medium model was constructed to calculate the percolation probability to quantitatively describe the permeability variation of oil shale with temperature. The test results indicated that the higher the temperature, the larger were the pore spaces. The increase in pore volume due to pyrolysis temperatures mainly affected the pores ranging from 10 nm to 100 nm and occurred in the specific temperature range (400 °C to 425 °C). Additionally, CT images show that the fracture morphology varied with increasing temperature and the number and length of fractures at different temperatures were in great accordance with the fractal law statistically. On the other hand, simulation of the percolation probabilities discovered that in a single pore media model over the whole range of tested temperatures they were too low to exceed the threshold. In contrast, in the dual medium model, the theoretical threshold of 31.16% was exceeded when the temperature reached 350 °C. Moreover, the results demonstrated that fractures dominated the seepage channel and had more significant effects on the permeability of oil shale. What has been done in this study will provide some guidance for the in situ fluidization mining of oil shale.

Acid mine drainage (AMD) is a hazardous by‐product of coal mining, which may intensify the creep deformation of cemented gangue backfill (CGB) in solid backfill mining. In this study, the long‐term stability and creep property of CGB soaked in AMD were quantitatively measured by experimental and theoretical analysis. The uniaxial compressive strength, elastic modulus, and mass of CGB soaked in AMD, with pH of 5.56 and soaking time of 30 to 360 days, were tested. The change trend of compressive strength, elasticity modulus, and mass first increased, then decreased, and finally ended at 94.37%, 96.68%, and 98.00%, respectively. The respective creep processes of CGB soaked in AMD and untreated CGB were similar, initial creep stage lasted only for a short time, and no creep deformation occurred in the steady creep stage. Moreover, the long‐term strength of CGB soaked in AMD was 98.6% of the untreated CGB. The creep law of the CGB soaked in AMD was accurately fitted by using the Kelvin model. The theoretical analysis revealed that the final creep deformation of the CGB column soaked in AMD was only 4.4 mm. The results of this paper show the possibility of using CGB in AMD‐accumulating goaf.