Slurry flow mechanism with time-varying viscosity in regional long-hole grouting for floor reinforcement

As deep coal mining has become more prevalent in China, ensuring production safety has become a significant concern due to complex geological conditions such as high-pressure water. To address the formation of water channels within the coal seam floor, regional grouting using long-hole drilling is a commonly employed on-site technique. This study focuses on analyzing the process of regional grouting using long-hole drilling based on field grouting projects. Theoretical models were developed for both overall and segmented grouting in near-horizontal drilling holes. Considering factors such as the time-dependent viscosity of cement slurry, pressure loss, and the gravity influence, calculation formulas were derived for different stages of long-hole grouting consisting of the grouting pressure in a single fracture. The validity of the calculation method, based on mathematical models, was confirmed by testing the distribution of cement hydration components using x-ray diffraction analysis. The grouting pressure gradually decreases along the branch hole because of slurry viscosity and pressure loss. The diffusion radius in a single grouted borehole exhibits a conical distribution along the spatial axis of the borehole. Building on these findings, the drawbacks associated with grout leakage in long-hole grouting were discussed, and its optimization methods were proposed, such as “staggered parallel grouting.” The results of this study are expected to provide theoretical guidance for the proactive prevention and control of water hazards in coal mines through the implementation of grouting techniques.