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The utilization of oil shale ash in developing environmentally sustainable filling materials for subterranean mines presents a promising ecological approach, albeit with typically low ash content. In this study, the filling material was prepared by adding oil shale ash and slag. The study examines the physical and mechanical properties of filling materials predominantly composed of oil shale ash slag, sourced from the Baoming open-pit mine in Jimusar, Xinjiang. Comprehensive testing and analysis are conducted to examine the chemical composition, mineral composition, and particle grading of oil shale ash, cement, and fly ash. The research prepared 45 cubic specimens measuring 50 mm × 50 mm × 50 mm and analyzed their mechanical responses under uniaxial compression conditions, employing varying dosages of ash, cementitious materials, and water as critical variables. The results indicate that the primary constituents of oil shale ash are silica (SiO2) and aluminum trioxide (Al2O3). When the oil shale ash content ranges from 60 to 70%, with a cement-fly ash ratio of 7:1 and a water content of 11%, the filling material attains its highest average compressive strength of 16.37 MPa at 28 days. Furthermore, increased cement content in the cementitious material correlates with higher compressive strength in the filling material. This research underscores the potential of oil shale ash–based green mining filling materials to restore goaf. [ABSTRACT FROM AUTHOR]

Under the condition of coal seam group occurrence, the gas sources in goaf cannot be determined when the protective coal seam is mined. To achieve the purpose of efficient gas control, it is necessary to analyze the gas sources in goaf in advance and carry out gas control for different gas sources. In this paper, the composition and stable carbon and hydrogen isotopes of desorption gases in main coal seams were tested and analyzed. Also, the gas sources and gas composition in the goaf of the protective coal seam are analyzed by establishing a quantitative identification model of mixed gas volume ratio. Gas source of the protective coal seam goaf is mainly M3 coal seam, accounted for 90%, M2 coal seam accounts for 9% on average, while M1 coal seam accounts for 1% on average, which indicates that the pressure-relief gas of M1 coal seam cannot enter goaf of M2 coal seam during M2 coal seam mining. This phenomenon makes M1 coal seam gas content constant and poses a safety risk of gas emission to the M1 coal seam. Therefore, the pressure-relief gas of the upper M1 coal seam has to be extracted to eliminate the hidden gas hazards when mining M2 coal seam (protective coal seam). Through the analysis of gas extraction concentration, it is found that after the formation of gas migration channels that used for gas flowing in the M1-protected coal seam, the migration channels can at least maintain until the working face of M2 protective coal seam is mined 350 m; this study can provide a certain reference for the gas control technology in protected coal seam under the condition of coal seam group mining. [ABSTRACT FROM AUTHOR]

In recent years, with the continuous construction of highways in Southwest China, highway tunnels inevitably have to pass through mine tunnels, which often happen. The tunnel passing through the coal mining area has an adverse impact on the stability of the rock around the tunnel, which leads to the instability of the rock around the tunnel and may collapse. It is of great practical significance to analyze and study the stability of surrounding rock in the section of highway tunnel crossing the mining area for ensuring the safety construction of tunnel crossing the mining area. With the continuous excavation of coal seam, the rock above the goaf will bend, fracture, and collapse. By monitoring the deformation of load and analyzing the parameters of geotechnical properties, it can effectively identify the deformation, overload damage, and rock cracks and other related problems. The optical fiber monitoring data of overburden is input into GIS to obtain the GIS state map in the process of coal mining. This paper discusses the properties of overload deformation and damage, and the division method of deformation zone. The existing control methods mainly follow the vertical stress, and cannot monitor the three-dimensional stress. In addition, most of these devices use electronic identification method, which has the disadvantage of weak anti electromagnetic interference ability, and cannot meet the requirements of three-dimensional stress monitoring. In this study, through the development of GIS technology, combined with the theory of flow stress and recovery, and aiming at the characteristics of FBG axial stress sensitivity, a three-dimensional stress-strain monitoring method of surrounding rock analysis based on FBG sensing technology is proposed. Based on this principle, a cubic three-dimensional stress FBG sensor is developed. This paper studies the stress-strain analysis of surrounding rock in goaf, and applies it to practical life, in order to promote its development and application. [ABSTRACT FROM AUTHOR]

To study the distribution law and flow field of gas concentration in goafs, using the goaf of the 714 working face in the Qinan Coal Mine as the engineering background, the gas concentration and flow field under different wind speeds were simulated based on the optimized porosity distribution model of gob caving rock using FLUENT software. The results show that, due to the influence of air leakage, the gas concentration in the shallow part of the goaf is greatly affected by the wind speed of the air intake air roadways, while the deep part of the goaf is nearly unaffected by the wind speed. When the wind speed of the intake air roadways is 1 m/s, there are three gas accumulation areas within the goaf, and, when the wind speed is between 2 and 3 m/s, there are only two gas accumulation areas. The distribution law of the gas concentration in the simulation results, based on the location of the gas accumulation areas and the rock properties of the "vertical three zones" in the goaf, informed the design of high-level drilling construction technology for the 714 working face of Qinan Coal Mine, and promising results are achieved. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to provide scientific basis for the stability evaluation of overburden rock of repeated mining goaf under the expressway. The objectives of the present study are to reveal the development of overburden rock fractures under repeated mining and to identify the fractal characteristics of the overburden rock fractures. The results show that (1) the separation fracture and vertical fracture fissure are developed in the overburden rock under repeated mining; (2) after the mining of the lower coal seam, the fractures developed in the overburden rock of the goaf are obviously retained in general. The number of fractures on both sides of the goaf is relatively large, while in the central part, it is relatively small and the fractures in most areas are basically closed; (3) under the same advancing length of working face in the lower coal seam, the fractal dimension in the caving zone is larger than that of the fractured zone; (4) with the increase of the advancing length of working face in the lower coal seam, the variation trend of the fractal dimension appears from small to large and then to small and stable; (5) when the repeated mining is over and the overburden rock movement is basically stable, the ratio of the fractal dimension in the caving zone and the fractured zone is 1.067:1. The results have an important reference value for ensuring the safety of the expressways above the repeated mining goaf in Shanxi region and similar areas. [ABSTRACT FROM AUTHOR]

Mine fire is a serious environment, health, and safety hazard throughout the world. Through analyzing the drawbacks of traditional extinguishing techniques on dealing with fire at top of goaf, we propose a new foam preparation method to make extinguishing foam. It uses a jet device to add foaming agent and a foam generator to produce foam. The driving powers are water pressure and compressed gas, which have strong intrinsic safety for application in underground coal mines. Testing results show that foam diffuses fast at the initial stage of infusion in the goaf, while the foam diffusion velocity finally maintains at 0.0084-0.0087 m/s. With a large tensile deformation, the foam flowing through a fracture aisle is within 0.4 s. The expansion foam accumulates upwards until it extinguishes fire at top of the goaf, making a sharp decrease on the fire source temperatures. It is feasible that foam is infused into the goaf discontinuously with an interval time less than the foam half-life to get a reasonable economic cost input and a good foam accumulation in the goaf. [ABSTRACT FROM AUTHOR]

This paper investigates the formation mechanism, relevant influential factors, and distribution laws of the collapse in the third mining area in Gong Changling District, Liaoyang City, China, by employing geological surveying, geophysical investigation, and theoretical analysis. The preliminary evaluation and prediction of ground settlement induced by the goaf collapse are presented. The results show that mining is the primary factor contributing to the ground subsidence and that groundwater infiltration accelerates this process. The three-zone model is proposed to analyse and evaluate the stability of the goaf. Based on this model, we conclude that the strata in the mined area and the surrounding non-mined area are unstable and could be subjected to ground subsidence and ground fissure once disturbed. [ABSTRACT FROM AUTHOR]

Due to coal mining taking place on a large scale in northern China, it is inevitable that wide-spread dewatering occurs in the aquifers overlying the resulting goaf. The purpose of this paper is to protect the groundwater of overlying unconsolidated aquifers. Based on physical model experiment, seepage experiments, and numerical simulation, this paper determines the patterns and distribution of the overburden rocks in the goaf, establishes the correlation between the fracture ratio and the hydraulic conductivity of the rock mass, and characterizes the groundwater flow pattern. The results show that (1) the residual fracture occurring ratio within the residual fracture zone is approximately 1.82 times that of the fracture compaction zone and 1.93 times that of the coal wall support zone; (2) the hydraulic conductivity of the rock mass in different parts of the goaf increases with increasing fracture ratio, the relationship of the two follows a power curve; (3) the predicted groundwater levels from numerical simulation is good fit with the measured and indicates that the hydraulic conductivities derived from seepage experiments are rational. We demonstrate how a laboratory-scale physical model can be used effectively to verify existing conceptual models in such a way that the impact of coal mining on groundwater resources can be predicted for similar regions. [ABSTRACT FROM AUTHOR]