Information on the ground fissures induced by coal mining is important to the safety of coal mine production and the management of environment in the mining area. In order to identify these fissures timely and accurately, a new method was proposed in the present paper, which is based on an unmanned aerial vehicle (UAV) equipped with a visible light camera and an infrared camera. According to such equipment, edge detection technology was used to detect mining-induced ground fissures. Field experiments show high efficiency of the UAV in monitoring the mining-induced ground fissures. Furthermore, a reasonable time period between 3:00 am and 5:00 am under the studied conditions helps UAV infrared remote sensing identify fissures preferably. The Roberts operator, Sobel operator, Prewitt operator, Canny operator and Laplacian operator were tested to detect the fissures in the visible image, infrared image and fused image. An improved edge detection method was proposed which based on the Laplacian of Gaussian, Canny and mathematical morphology operators. The peak signal-to-noise rate, effective edge rate, Pratt’s figure of merit and F-measure indicated that the proposed method was superior to the other methods. In addition, the fissures in infrared images at different times can be accurately detected by the proposed method except at 7:00 am, 1:00 pm and 3:00 pm.

To explore the strength development characteristics and engineering performance of different coal-based solid waste filling materials cemented into filling body, coal gangue was used as coarse material, fly ash, desulfurization gypsum, gasification slag, and furnace bottom slag as fine material, and cement as a gelling agent. The uniaxial compressive strength (UCS) and bleeding rate of coal-based solid waste cemented backfill (CBSWCB) were tested by an orthogonal experiment, and the influencing factors of mechanical properties and strength development were analyzed. The multiple generalized linear model of strength and bleeding rate was established, and the optimal filling material ratio was determined. The engineering performance index of CBSWCB with the optimal ratio was tested. The results show the following points: (1) the concentration and content of desulfurization gypsum had a great influence on the early compressive strength of CBSWCB, while fly ash, gasification slag, and furnace bottom slag had little influence on the early compressive strength. (2) High concentration, high content of fly ash and furnace bottom slag, low content of desulfurization gypsum, and gasification slag can significantly improve the early strength. High concentration and high content of fly ash, low content of gasification slag, furnace bottom slag, and desulfurization gypsum are beneficial to the later strength increase. (3) Under the optimal ratio scheme, the bleeding rate of CBSWCB was 1.6%, the slump was 16.6 cm, the cohesion was general, the segregation resistance was good, the initial setting time was 5.42 h, the final setting time was 7 h, and the early strength after curing for 8 h reached 0.24 MPa.

The large production and low comprehensive utilization rate of solid waste from coal power base affects the efficient and coordinated development of regional resources and the ecological environment. In order to promote utilization of solid waste from coal power base, coal gangue, fly ash, and gasification slag are mixed as raw materials to prepare filling materials, and a study on the evolution law of the mechanical properties of coal-based solid waste filling body is systematically carried out. After clarifying the physical and chemical properties of the filling materials, the Box–Behnken experimental design method was used to study the effects of slurry mass fraction, coal gangue, fly ash, and gasification slag on the strength of the filling body based on the response surface-satisfaction function coupling theory. Furthermore, a multivariate nonlinear regression model was constructed for the strength of the filling body at different maintenance ages. Based on the analysis of variance (ANOVA) and the response surface function, the impact mechanism of influencing factors and their interaction on the strength of filler were revealed. The results show that the strength of the filler is affected by single factors and interactions between factors. The interaction of slurry mass fraction and gangue dosing has a significant effect on the strength of the filler in the early stage; the interaction of fly ash and gangue dosing has a significant effect on the strength of the filler in the middle stage; the interaction of slurry mass fraction and gasification slag dosing has a significant effect on the strength of the filler in the final stage. The mixed filling materials significantly affect the strength of the filler as the maintenance time is extended. The mixed filling materials are extensively interlaced with the hydration products, calcium alumina, and calcium silicate hydrate (C-S-H) gel, forming a stable three-dimensional spatial support system as the maintenance time increases. The best ratio to meet the requirements of mine filling slurry pipeline transportation and filling body strength was selected using the regression model and the proposed economic function of filling material.

It has been proven that it is a feasible treatment method to prepare paste filling material from coal-based solid waste to fill underground goaf. Based on the complexity of the goaf environment, especially the influence of humidity on paste filling materials, this paper prepared paste filling materials with a mass concentration of 80% by using coal gangue and fly ash, and carried out a uniaxial compression test of coal-based solid waste paste filling materials under four different water-bearing states. The experimental results show that: (1) The binary primary equation fits well the variation trend of paste filling strength with water content. With the increase of moisture content, the compressive strength of paste filling material gradually decreases, and the higher the moisture content, the more obvious the influence on the strength of paste filling. (2) The damage evolution equation and constitutive equation of paste filling materials with different moisture content were established. With the increase of strain, the influence of moisture content on the damage of paste filling material decreases gradually, and the moisture content can promote the damage development of paste filling material to a certain extent. (3) The influence mechanism of moisture content on coal based-solid waste paste filling material is discussed from the three aspects of physical effect, structural effect and chemical effect, which provides a direction for further research on the influence mechanism of moisture content on filling strength. The research on the failure mechanism of coal-based solid waste paste filling and the safety production of the mine can be used as a theoretical support.

To study the stability control of stope mining roadways below remaining coal pillars, the present study investigates the destabilization mechanism of coal pillars and roadways in sections under the dual action of supporting pressure on the floor of the remaining coal pillar in the overlying coal seam and the mining at the working face of the lower coal seam and clarify the principle of surrounding rock stability control based on theoretical analysis, numerical simulation, and industrial testing. The results yielded the following findings. After the stope mining of the overlying coal seam working face, the stress transfer of the T-shaped remaining coal pillar significantly increased the vertical stress of the lower coal seam. The lateral support pressure generated by the stope mining at the lower coal seam working face further aggravated the stress concentration in the coal, leading to severe compression-shear failure of the surrounding rock. As the sectional coal pillar becomes wider, the roadway gradually avoids the area of peak superimposed support pressure. The vertical stress curve of the sectional coal pillar shifts from single-peaked to asymmetrically double-peaked, and the stress difference between the two roadway ribs and the stress concentration coefficients decrease continuously. A stability control method of long anchor cable reinforcement support is proposed. In-situ industrial testing showed that the surrounding rock deformation was basically stable during the service period of the 42202 stope mining roadway, thus achieving the stability control of the stope mining roadway.

In order to deeply study the basic characteristics, diffusion laws, and flow laws of coal gangue and coal gangue slurry, the basic characteristic parameters of coal gangue and coal gangue slurry were obtained through particle size distribution test, electron microscope scanning test, X-ray diffraction test, X-ray fluorescence spectrum test, and angle of repose test. The conveying performance test of coal gangue slurry was carried out, and based on this, a simulation test of coal gangue slurry caving areas was designed. The diffusion and flow laws of coal gangue slurry under the same inclination angle were summarized, and the field test of fluidization filling in the caving areas was conducted. The results show that: (1) The water-to-gangue ratio was the main controlling factor for the conveying performance of coal gangue slurry. The extensibility, slump, and bleeding rate of the coal gangue slurry increased with the increase of the water-to-gangue ratio. (2) The diffusion profile of coal gangue slurry at different dip angles was arc-shaped, and the diffusion distance of slurry increased with the increase of infiltration time. However, there were differences in the sustained diffusion ability of different dip angles. (3) At the same time interval, the spatial accumulation patterns of scattered gangue in different regions will lead to differences in the diffusion speed of the slurry. (4) Both burying and hanging pipes in the falling area can safely and efficiently fill the gangue slurry. The diffusion distance of the caving areas in the test working face was basically consistent with the diffusion distance of the slurry in the simulation test of the coal gangue slurry caving areas.