186 technologies, including long-distance precision drilling, geological identification, and highpressure segmented grouting. Its reliability and replicability are validated through multiple engineering applications, with the objective of providing an effective technical solution for ensuring the safe construction of deeply buried water diversion tunnels in western China. 2. Geological Characteristics of Fault Fracture Zones in Long, deeply buried water diversion Tunnels and Current Status of Conventional In-Tunnel Grouting Technology 2.1 Engineering Geological Characteristics of Fault Fracture Zones in Long, deeply buried water diversion Tunnels The geological structure of these tunnel sections is highly complex. Rock masses within fractured zones are predominantly fragmented, granular, or argillized and are frequently associated with karstified strata. Deep burial conditions generate a pronounced “three-high” environment, characterized by high ground stress, high external water pressure, and high ground temperature, with tunnel depths generally exceeding 600 m, posing systematic threats to construction safety (Niu and Zhang, 2019). Hazard types are both prominent and high risk, as collapses, mud and water inrush, and large deformation of soft rock frequently occur during construction. Fault zones exhibit extensive influence ranges and complex spatial distributions, with the width of a single fractured zone generally exceeding 100 m and showing marked spatial heterogeneity. 2.2 Limitations of In-Tunnel Treatment Technology Due to limitations in drilling length and grouting technology, the length of a single treatment cycle is typically restricted to approximately 30 m. For large-scale fault zones extending several hundred meters, segmented treatment must be repeatedly implemented, resulting in prolonged construction durations. In addition, confined operating space and existing support structures within tunnels impose constraints on grouting pressure, which is generally maintained below 5 MPa, limiting the effective slurry diffusion radius. Furthermore, dense fullface drilling at the working face is difficult to implement, particularly under TBM tunneling conditions, where feasibility is significantly reduced. Drilling operations are also prone to disturbing concealed hydrological channels, increasing the likelihood of inducing secondary disasters such as water inrush and collapse. 3. Surface Directional Drilling High-Pressure Grouting Technology for Complex Formations in Long, Deeply Buried Water Diversion Tunnels 3.1 Challenges Faced by Surface Directional Drilling Grouting for Long, Deeply Buried Water Diversion Tunnels 3.1.1 High Requirements for Drilling Accuracy and Efficiency The implementation of kilometer-level directional drilling in water-rich fractured strata requires the realization of precise three-dimensional positioning and parallel borehole
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