1446 Surface pre-grouting technology exhibits advantages, including no occupation of working face time, flexible equipment deployment, high attainable grouting pressure, wide slurry diffusion range, enhanced construction safety, effectively mitigating the risks of water inrush and surrounding rock instability (Tong et al., 2022; Liu et al., 2024). Originating in the coal mining industry in China, this technology has undergone sustained advancements in grouting materials, equipment, techniques, and operational processes since its initial successful application in 1958 (Hong, 2006). In 2010, kilometer-level shaft grouting was achieved, reaching a maximum depth of 1355 m (Gao, 2017; Gao, 2020). In recent years, through deep integration with directional drilling techniques, China Coal Technology and Engineering Group, Beijing Mine Construction Research Institute has developed the “L”-shaped directional hole grouting technology (Li et al., 2023). This method has been successfully applied in coal mine floor and roof water hazard control, roadway surrounding rock reinforcement, and emergency response to water inrush events (Yang et al., 2023). However, when extended to large fault-fractured zones in deeply buried water diversion tunnels, the technology continues to face substantial challenges, including difficulty in drilling trajectory control, low drilling efficiency, and insufficient understanding of slurry diffusion mechanisms, which have resulted in limited applications in water diversion tunnels. This study systematically examines the geological characteristics of long, deeply buried water diversion tunnels and reviews the current development status of in-tunnel grouting technologies. Based on the accumulated experience of surface pre-grouting practices in coal mines, a targeted technical system suitable for hazard prevention and control in water-rich fractured strata of deeply buried water diversion tunnels is proposed. The system integrates core technologies, including long-distance precision drilling, geological identification, and high-pressure segmented grouting. Its reliability and replicability are validated through multiple engineering applications, with the objective of providing an effective technical solution for ensuring the safe construction of deeply buried water diversion tunnels in western China. 2. GEOLOGICAL CHARACTERISTICS OF FAULT FRACTURE ZONES IN LONG, DEEPLY BURIED WATER DIVERSION TUNNELS AND CURRENT STATUS OF CONVENTIONAL IN- TUNNEL GROUTING TECHNOLOGY 2.1 Engineering Geological Characteristics of Fault Fracture Zones in Long, deeply buried water diversion Tunnels The geological structure of these tunnel sections is highly complex. Rock masses within fractured zones are predominantly fragmented, granular, or argillized and are frequently associated with karstified strata. Deep burial conditions generate a pronounced “three-high” environment, characterized by high ground stress, high external water pressure, and high ground temperature, with tunnel depths generally exceeding 600 m, posing systematic threats to construction safety (Niu and Zhang, 2019). Hazard types are both prominent and high risk, as collapses, mud and water inrush, and large deformation of soft rock frequently occur during construction. Fault zones exhibit extensive influence ranges and complex spatial distributions, with the width of a single fractured zone generally exceeding 100 m and showing marked spatial heterogeneity. 2.2 Limitations of In-Tunnel Treatment Technology Due to limitations in drilling length and grouting technology, the length of a single treatment cycle is typically restricted to approximately 30 m. For large-scale fault zones extending several hundred meters, segmented treatment must be repeatedly implemented, resulting in prolonged construction durations. In addition, confined operating space and existing support structures within tunnels impose constraints on grouting pressure, which is generally maintained below 5 MPa, limiting the effective slurry diffusion radius. Furthermore, dense full-face drilling at the working face is difficult to implement, particularly under TBM tunneling conditions, where feasibility is significantly reduced. Drilling operations are also prone to
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