Research on the mechanism of fracture grouting diffusion and its application based on slurry-rock mass coupling effect

The deep mining process of North China type coalfields is highly threatened by the threat of water damage from the floor limestone aquifer. By arranging grouting holes reasonably to inject a large amount of slurry into the aquifer that directly threatens the safety of coal seam mining, making the strong aquifer a weak aquifer or an impermeable layer is the main means to solve such water damage problems. In microfracture grouting engineering, the slurry-rock mass coupling effect has a significant impact on the diffusion process of slurry. To this end, the interaction between slurry and rock mass and the diffusion mechanism of slurry during high-pressure grouting of coal seam floor aquifers was studied, a single fracture grouting diffusion theoretical model was established that considers the slurry flow-rock mass deformation coupling effect, based on the viscosity time varying Bingham slurry diffusion equation and fracture aperture control equation. The spatial distribution characteristics of slurry pressure and fracture aperture in the slurry diffusion direction were analyzed, and the effect rules of slurry-rock mass coupling effect on slurry diffusion was revealed, and the results were compared with the grouting model with constant fracture aperture. The results showed that the attenuation trend of slurry pressure and fracture aperture in the slurry diffusion direction was consistent, and both had obvious nonlinear characteristics, and the attenuation was faster in the fracture entrance area. The degree of slurry-rock mass coupling effect decreased with the increase of fracture aperture, and the design value of grouting pressure will be too high if fracture aperture was small and the slurry-rock mass coupling effect was not considered. The grouting pressure became the main controlling factor affecting the slurry diffusion distance gradually as the fracture aperture increased. By comparing the theoretical results with an example of grouting transformation of the limestone aquifer in the lower coal seam floor of Luxi coal mine, the validity of the theoretical model was verified.