192 4.2 Case Ⅱ: East Main Line Tunnel Treatment Project of the Central Yellow River Diversion Project The tunnel passes through Ordovician limestone, strong karst water-rich strata, with a total length of 28.763 km, a maximum burial depth of 697 m, a designed excavation diameter of 4.11 m, and a water pressure ranging from 2.45 to 2.73 MPa. The maximum water inrush volume during the early stage reached 17,000 m³/h. For the remaining 5941 m section with extremely high-water inrush risk, surface directional, six boreholes were arranged in a ring along the tunnel contour, with differentiated grouting designs, as shown in Figure 7. To date, treatment of 2400 m of tunnel sections has been completed. After treatment, the water permeability coefficient was reduced to less than 2Lu, of which 751 m has been successfully excavated. No water inrush accidents occurred during TBM tunneling, and the average daily advance rate reached 10 m, enabling safe and efficient construction in strongly water-rich strata. Figure 7 – Grouting hole layout diagram for TBM-Excavated tunnel 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-explorationgrouting 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 faultfractured 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.
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