1452 4.3 Case Ⅲ:Yangtze River to Hanjiang River Water Diversion Tunnel Treatment Project of the South-to-North Water Diversion Project This project traverses multiple deep and large fault zones, with a maximum burial depth of 1230 m, a designed tunnel diameter ranging from 10.3 to 10.5 m, a maximum water pressure of 5.7 MPa, and a total length of 3.1 km of tunnel sections predicted to have high risks of mud and water inrush. Since the initiation of the project, surface directional drilling-exploration-grouting integration technology has been applied for hazard prevention and control. Ten grouting boreholes were arranged in a ring along the tunnel cross-section within the fault-fractured zone, with a borehole arrangement radius of 11.75 m and a spacing of 7.26 m (Figure 8). In this project, a high-pressure perforated casing retreat grouting process was innovatively adopted, achieving precise grouting under a high pressure of 30 MPa for the first time, with the maximum single grouting volume exceeding 600 m³. This technology shortened the grouting construction period by more than 30%, significantly enhancing the efficiency and reliability of fault treatment under conditions of ultra-deep burial and ultra-high water pressure. Figure 8 – Grouting hole layout diagram for large-diameter tunnel 5. CONCLUSIONS (1) Based on the mechanisms of water plugging and structural reinforcement in water-rich faultfractured zones, together with the concept of active hazard prevention and control, a surface directional drilling-exploration-grouting integrated system for hazard prevention and control in water-rich fractured strata of long, deeply buried water diversion tunnels is established. This integrated system encompasses a complete technical chain that includes materials, construction processes, and specialized equipment, providing a novel and systematic solution for hazard treatment in deeply buried water diversion projects. (2) Engineering practice demonstrates that the drilling-exploration-grouting integrated technology for hazard prevention and control in water-rich fractured strata of long, deeply buried water diversion tunnels achieves the construction of an ultra-long, effective waterproofing and reinforcement curtain in a single operation. This approach effectively resolves the critical bottleneck associated with mud and water inrush during tunnel excavation, and its treatment capacity for fault-fractured zones in kilometer-level deep water conservancy tunnels is verified through practical application. (3) With the continuous advancement in research into the deep underground multi-field coupling environment and slurry diffusion mechanisms, the technical system for surface directional drilling and grouting will be progressively refined. It not only serves as an effective solution to tackle complex geological hazards in deeply buried water conveyance tunnels, but is also poised to evolve into a vital technical underpinning for ensuring the safe and efficient exploitation of deep mineral resources in the future
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