1451 Figure 5 – Grouting hole layout diagram for drill-and-blast tunnel Figure 6 – Grout veins exposed by the tunnel working face 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
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