Numerical Simulation of Grout Diffusion and Overlap Characteristics in Horizontal Curtain Grouting for Underground Mines Within 3D Discrete Fracture Networks

Deep metal mines face increasing risks of water and sand inrush under complex fracture network conditions, where the unclear mechanism of slurry diffusion limits the reliability of horizontal curtain grouting. Taking the Cuihongshan iron–polymetallic mine as a case study, this paper establishes a stochastic three-dimensional discrete fracture network model and adopts an orthogonal experimental design to systematically investigate the effects of key engineering parameters on grout diffusion behavior. The results reveal that grouting pressure acts as the dominant controlling factor, significantly expanding the diffusion range and promoting the formation of continuous high-fill zones within the fracture network. Conversely, slurry viscosity exhibits a negative correlation with diffusion performance, leading to reduced inter-borehole connectivity as viscosity increases. Compared with conventional macro-indicators, the inter-borehole overlap rate provides a more precise quantitative measure of curtain continuity. The study demonstrates that achieving a sufficiently high overlap rate is critical for transitioning from discontinuous filling to a reliable impermeable curtain. These findings offer a theoretical basis for optimizing grouting parameters and evaluating sealing effectiveness in deep mine construction.