Research and Development of New Slurry Sealing Materials Based on Box–Behnken Design and Multi-Performance Synergistic Regulation

To address gas leakage in coal mine gas extraction boreholes, this study developed a novel slurry-based sealing material using sodium bentonite as the matrix, compounded with sodium dodecylbenzene sulfonate as the dispersant and sodium carboxymethyl cellulose as the thickener. The optimal formulation, determined through single-factor experiments and response surface methodology, consisted of a water-to-bentonite ratio of 4.4:1, a dispersant content of 0.41%, and a thickener content of 0.12%. Under these conditions, the slurry exhibited a flowability of 134.8 mm, a water retention rate of 96.01%, and a permeability of 41.45%, representing improvements of 10.74%, 11.74%, and 14.47%, respectively, compared with the unmodified bentonite material. Fracture seepage tests further demonstrated that the modified slurry exhibited superior permeability to cement-based materials under different fracture porosities and grouting pressures. In addition, results from a self-designed airtightness testing platform showed that the material maintained excellent sealing performance under positive pressures of 0.1–0.3 MPa, with a significantly lower pressure decay rate than those of cement and polyurethane materials. These findings indicate that the proposed bentonite-based slurry provides an effective sealing material for coal mine gas extraction boreholes and may contribute to safer and more efficient coal mine production.