185 KEYWORDS Mud and water inrush, Ground grouting, Fault fracture section, Diversion tunnel, Water plugging reinforcement. 1. INTRODUCTION Deep and long tunnels constitute critical components of national major infrastructure and play an irreplaceable strategic role in water resource allocation, energy transmission, and transportation corridor development (Xie et al., 2022). With the continuous expansion of water conservancy projects into high-altitude and tectonically active regions of western China, tunnel construction increasingly encounters compounded adverse conditions, including high ground stress, high external water pressure, elevated ground temperature, and strong construction disturbance. Excavation within weak and fractured strata is highly susceptible to severe engineering risks, such as mud and water inrush, excessive deformation of surrounding rock, and TBM jamming, which significantly constrain construction safety and operational efficiency (Zhang, 2025; He et al., 2023). Therefore, the effective prevention and control of mud and water inrush disasters of unfavorable geological conditions in deep and long tunnels, have emerged as urgent technical bottlenecks requiring systematic resolution. 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 faultfractured 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
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