191 fracture water plugging, while chemical slurry is employed for permeation grouting in porous and fine sand layers. 4. APPLICATION PRACTICE 4.1 Case Ⅰ: Xianglushan Tunnel Treatment Project of the Central Yunnan Water Diversion Project The No. 5 Adit of this tunnel traverses the Shihuiyao Fault Zone, with a total length of 1245.9 m and a maximum overburden depth of 552 m. The surrounding rock is highly fractured, the external water pressure ranges from 1.00 to 2.11 MPa, and the maximum mud and water inrush volume during the early stage reached 1000 m³. Following in-tunnel grouting, the monthly advance rate was limited to 3.3–4.7 m. For the remaining 552 m unexcavated section, surface directional drilling and grouting technology were applied for the first time to conduct water-blocking and reinforcement treatment of the tuff stratum, with six kilometer-scale highprecision boreholes completed and a deviation rate of ≤ 1.9‰ (Figure 5). The maximum grouting pressure reached 15.06 MPa, and the total grouting volume amounted to 92612.70 m³. After treatment, the stratum water permeability coefficient was reduced to below 2 Lu, the selfstability of the surrounding rock was upgraded to Class Ⅲ, and the working face remained dry without water inrush. Slurry diffusion traces were clearly observed, the fracture sealing rate exceeded 90%, and the water-stop curtain range exceeded 8 m (Figure 6). Therefore, the monthly advance rate of the drill-and-blast method increased to 60 m, representing an approximately 15-fold improvement in construction efficiency. Figure 5 – Grouting hole layout diagram for drill-and-blast tunnel Figure 6 – Grout veins exposed by the tunnel working face
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