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To solve the problem of gangue discharge in coal mining, fluidized gangue filling technology was developed. The key scientific problem of this technology is the diffusion characteristics of the gangue in the goaf. Therefore, a discrete element fluidized gangue model was established based on the ARR contact model. Based on the Rblock module, a goaf model with a certain void ratio was created, and the meso-parameters of fluidized gangue were calibrated. The fluidized gangue diffusion and rock displacement laws were explored under different grouting speeds, void ratios, and gangue particle sizes. The research results show that with the increase in the grouting speed and void ratio, and the decrease in the gangue particle size, the diffusion radius gradually increases, and the rock displacement in the goaf also gradually increases. Under given geological conditions, the total grouting mass of a single hole can reach 5.63 × 104 kg. [ABSTRACT FROM AUTHOR]

The overlying rock structure and stress process are systematically analyzed to solve the coal pillar instability caused by the gangue fluidized filling process. The stability model of the key block above the coal pillar and the stability model of the coal pillar were respectively established. The key block instability criterion was obtained through a theoretical analysis of the key block balance equation. In combination with the theory of the plastic zone, the criterion of unstable coal pillars is proposed. The above calculation demonstrates that the pressure of the overburden, the width of the coal pillar, the elastic foundation coefficient of the gangue, and the grouting pressure are the main factors affecting the stability of the coal pillar. Based on the specific geological conditions of Pingmei No. 12 Mine, more calculations are derived: the width of a side of the plastic zone of the coal pillar is only 0.80 m, and the coal pillar will not be damaged during the filling process, and the stability is good. [ABSTRACT FROM AUTHOR]