Evaluation of Pore Structure Characteristics and Permeability of In Situ-Blasted Leachable Ore in Stopes Under Varying Particle-Size Gradations

In recent years, in situ blasting–leaching, in the stope has emerged as an economically viable and environmentally sustainable mining technique for low-grade ore deposits. While the leaching efficiency is influenced by factors such as ore type, solution composition, and spraying speed, the most significant factor is the effect of post-blasting crushed-stone particle size and gradation on the pore structure, which subsequently influences seepage and leaching performance. To investigate how particle size and gradation affect the pore structure of granular media, physical models of ore particles with varying sizes and gradations were constructed. These models were scanned and three-dimensionally reconstructed using CT scanning technology and Avizo software (Avizo, Version 2023.1; Thermo Fisher Scientific: Waltham, MA, USA, 2023) enabling quantitative analysis of pore structure parameters. The results indicate that the coefficient of uniformity (Cu) is approximately negatively correlated with porosity, while the vertical absolute permeability (kz) follows an attenuated exponential trend. When the fine-particle content (L8 > L3 > L1) increases by 1.5-fold and 9-fold, the number of pore throats increases by 8.71% and 30.91%, respectively, the average pore size decreases by 75.1% and 64.4%, the average throat size decreases by 66.3% and 60%, and the connectivity rate decreases by 92% and 77.8%. This study further evaluates permeability based on the aforementioned pore structure parameters. Multiple regression analysis reveals that the connectivity rate and throat size have the most significant influence on permeability. Accordingly, permeability analysis and prediction are conducted using the improved Purcell formula, which demonstrates a strong correlation with the experimentally measured results.