Field application and diffusion law of grouting slurry in floor aquifer of a coal mine

Floor aquifers are responsible for approximately 55% of water inrush incidents in coal mines. As mining depths increase, the risk posed by confined floor aquifers becomes more severe. Grouting reinforcement and the sealing of water channels in the mine floor have been widely adopted as mitigation measures. This study investigates the flow and diffusion behavior of grout under hydro-static pressure by examining the fundamental properties of two grout types-pure cement slurry and cement-clay mixture-through orthogonal testing. The influence of grout specific gravity on key properties, including viscosity, bleeding rate, stone formation rate, setting time, and compressive strength, is analyzed. Furthermore, a mechanical model based on grout-rock coupled seepage theory is implemented in COMSOL Multiphysics to simulate grout diffusion. The effects of initial grouting pressure, initial porosity, and initial fracture aperture on grout diffusion radius and rate are systematically evaluated. Results indicate that viscosity, stone formation rate, and compressive strength of both grouts increase with specific gravity, whereas bleeding rate and setting time decrease. Based on the performance tests, mix A2 (pure cement) and B1 (cement-clay) are identified as the optimal proportions for their respective grout types. As grouting pressure decreases, the slurry flow rate gradually slows, and the grouting pressure approaches but remains slightly above the hydro-static pressure. The diffusion rate and radius of grout are positively correlated with the initial fracture aperture and porosity. Once porosity exceeds a critical threshold, grout rapidly infiltrates the fracture, after which the flow rate declines steadily. In a field application, an optimized slurry ratio was employed to treat an aquifer within a coal seam floor at a depth of 140 m. Field surveys confirmed that the grouting parameters satisfied the design requirements, and the grouting performance was effective.