Main Controlling Factors of Slurry Migration During Grouting at the Top of Ordovician Limestone Aquifer

Floor Ordovician karst confined water inrush severely restricts safe exploitation of lower coal seams across North China-type coal basins. Surface directional drilling regional grouting serves as the dominant aquiclude reconstruction technology for water hazard mitigation, yet existing research lacks quantitative decoupling and hierarchical sensitivity quantification of medium intrinsic attributes and controllable grouting parameters. To resolve this knowledge gap, this work delineates five core governing variables: porous medium permeability, matrix porosity, injection pressure, slurry dynamic viscosity and slurry bulk density. A coupled Darcy–Bingham two-phase flow numerical framework based on the COMSOL Multiphysics fluid–solid interaction module is constructed—combined with L25(56) orthogonal experimental design to quantitatively characterize the gradient response law of slurry effective diffusion volume against multi-factor perturbation. Variance analysis (ANOVA) demonstrates a hierarchical control sequence: porous medium permeability > matrix porosity > grouting pressure > slurry dynamic viscosity > slurry bulk density. Medium permeability, porosity and injection pressure dominate slurry migration behavior with diffusion volume perturbation amplitudes ranging 2–191%; whereas, rheological and density parameters exert secondary marginal effects limited within 1–8%. Fracture hydraulic theoretical interpretation reveals permeability acts as the primary groutability discriminant index, and injection pressure exhibits prominent marginal diminishing effect with an efficiency threshold of 8 MPa. This study establishes a quantitative parameter optimization framework for Ordovician top aquiclude reconstruction engineering, providing theoretical support for targeted grouting parameter regulation and risk reduction in blind high-pressure injection.