Experimental Study on the Diffusion Law of Coal-Based Solid Waste Slurry with Grouting Filling in the Gangue Voids of the Caving Zone.

Due to the concealment of the caving zone, it is difficult to detect and grasp the diffusion law of the slurry in the voids of the gangue pile. On the preparation of reasonable grouting filling materials, a large-scale three-dimensional gangue grouting filling test system has been established to detect the slurry pressure and resistivity inside the gangue pile and analyze the flow pattern of the slurry in the voids of the gangue pile. The research results show that the slump and bleeding rate of the filling slurry are significantly reduced with the increase of the fly ash content. The optimal ratio of fly ash, coal gangue, and gasification slag is 7:2:1, with a mass fraction of 72%. In the process of grouting, the internal pressure of the gangue pile can be divided into the initial stable stage, the step growth stage, and the pressure stability stage, and the change curve of the pressure sensor at the lower level is similar. The resistance value of the original broken gangue in the experiment is approximately 1600 Ω. Grouting filling forms a slurry-rock mixture, and its resistance continuously decreases with the stable injection of the slurry (minimum value 150 Ω). It is determined that the slurry near the grouting hole mainly diffuses longitudinally with a good void filling effect. The void channels of slurry diffusion are randomly distributed and have different shapes, which hinder slurry flow and diffusion. Slurry particles accumulate and settle at local small voids. Meanwhile, the surface of the gangue blocks is dry, and the slurry absorbs part of the water during diffusion, resulting in the increase of the slurry concentration and the weakening of the lateral diffusion ability. Secondary or multiple grouting can effectively fill the void of the broken gangue and further improve the filling effect.