From the perspective of resource recovery and environmental protection, coal gangue-fly ash cemented backfill coal mining has become an important direction for the green development of coal mines in recent years. Analysis of the rheological parameters of backfill slurry is the basic principle to design a backfill pipeline system. Coal gangue-fly ash backfill slurry has a mass concentration of 76% to 79% and a maximum particle size 20 mm. Therefore, it is difficult to use conventional rheometers for experimental analyses of the rheological parameters of such fluids. We developed a rheometer for high-concentration coal gangue backfill slurry (HCGS rheometer) based on the coal gangue-fly ash backfill practice of Gonggeying Mine, and analyzed the rheological properties of the backfill slurry. The experimental results showed that the Reynolds number of the coal gangue-fly ash backfill slurry was much smaller than the critical Reynolds number, indicating the flow state in the pipeline was laminar. Based on these results, it may be more appropriate to control the mass concentration to 77% to 78%, and the suggested fly ash content is 25%. This work provides a scientific basis to optimize the backfill parameters and pipeline system in coal mines.

In order to explore the stability of overburden rock and the development height of water flowing fractured zone in roadway filling mining, based on the movement and deformation mechanism of overburden rock, the mechanical analysis of overburden stability and failure was carried out, and the mechanical model of main roof rock beam was established, and the ultimate span and limit deflection of rock beam fracture were deduced. Combined with the mechanical model of the main roof fractured rock, the basis for the judgment of overburden failure developing to fractured zone is given in this paper. Taking a coal mine roadway backfill under water-bearing stratum as an example, based on the equivalent mining height, the theoretical calculation and analysis are carried out on the stability of overburden rock and the height of water flowing fractured zone. The reliability of the theoretical analysis is verified compared with the empirical formula and the numerical simulation results. The results showed that the water flowing fractured zone developed to the bottom of no. 7 glutenite, with a height of 32.5 m, slightly less than the calculation result of the empirical formula. The thickness of the waterproof coal pillar was 39.8 m, which was much less than the distance from the aquifer to the coal seam and can be mined safely.

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To find out the effect of total tailing particle size and grading on the rheological property of filling slurry with high concentration, especially in high intensity, the experiment on the particle size of total tailings was conducted firstly to get the corresponding result. Then, the collapse test of mixed slurry with different cement tailing ratios and different concentrations was carried out to get the corresponding slump value and extension value. Furthermore, the rotational viscometer was applied to test shear stress in the samples with different cement tailing ratios and different concentrations, from which the relevant rheological parameter can be achieved through the Bingham rheological model. Finally, a strength test to mixed slurry block with different cement tailing ratios and different concentrations was conducted (3 days, 7 days, and 28 days); the corresponding intensity values were taken. The experiment result illustrates that with the increase of concentration and cement tailing ratio of the slurry, the collapse degree and extended degree of slurry decreased, while yield stress, plastic viscosity, and strength increased. When the concentration was raised from 70% to 72%, all parameters that characterize good fluidity reduced obviously. As a result, the mixed slurry with a concentration of 70% and cement tailing ratio of 1 : 8 not only meets the requirements of production intensity but also has good mobility and low pipeline wear.

Supply of cheap and abundant raw materials is a key factor in reducing the cost of cemented filling materials. To solve this problems of the high cost of cemented filling materials and insufficient sources of raw materials, an experimental study on cemented filling material with a large mass ratio of construction demolition waste was performed. A large amount of recycled aggregate of construction demolition waste was added to cemented material to prepare a high concentration slurry, from which the influences of aggregate/cement mass ratio, admixture/cement mass ratio, water/solid mass ratio, recycled aggregate gradation and mud content of recycled aggregate on slump, setting time and compressive strength of cemented filling material with a large mass ratio of construction demolition waste were analysed via the orthogonal test method and regression equation analysis. Finally, an industrial formula for cemented filling material with a large mass ratio of construction demolition waste was determined, and the mechanical and microscopic properties were analysed. The results indicate that the industrial formula with an aggregate/cement mass ratio of 3.0, an admixture/cement mass ratio of 1.5%, a water/solid mass ratio of 0.35, a recycled aggregate gradation of 40:30:15:15, a mud content of recycled aggregate of 0ཞ4% and a mass ratio of construction demolition waste to solid material of 75% exhibits the properties of rapid strength growth and high residual strength, and can be applied in underground coal mines conditions.