1447 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 distribution within heterogeneous fractured rock masses. Under such geological conditions, drill bits are highly susceptible to uncontrollable deviation, while borehole instability phenomena, including collapse and shrinkage, occur frequently, leading to a high incidence of downhole accidents and significantly reduced drilling efficiency. 3.1.2 Unclear Prior Deep Geological Information For large fault -fractured zones, existing geological exploration data is severely insufficient. Influenced by complex mountainous terrain and deep burial conditions, surface geophysical prospecting exhibits limited resolution, which restricts the accurate identification of deep small-scale geological structures. Drilling construction is therefore characterized by sparse and discontinuous data acquisition, preventing the establishment of reliable and precise geological models. 3.1.3 Insufficient Adaptability of Surface Grouting Treatment Technology At present, there remains a lack of high-pressure segmented grouting materials, construction processes, and specialized equipment suitable for horizontal boreholes in fractured rock masses. Moreover, key process parameters, including slurry diffusion behavior and grouting pressure control, lack comprehensive theoretical support and standardized technical guidance. 3.2 Theoretical framework of active protection for Long, Deeply Buried Water Diversion Tunnels 3.2.1 Mechanism of Grouting Water Plugging and Reinforcement for Water-Rich Fault Fracture Zones The stratigraphic structure of large fault-fractured zones is highly complex and variable and is commonly classified into fracture-developed zones, cataclastic zones, and crushed zones, including argillized and sandy zones. Slurry diffusion mechanisms differ significantly among these strata. In fracture-developed and cataclastic zones, cement-based slurry primarily diffuses through fracture networks via permeation (Figure 1). In sandy and argillaceous crushed zones, slurry reinforcement is mainly achieved through pore permeation, high-pressure splitting, and compaction effects (Figure 2). The effective slurry diffusion radius represents a critical parameter for determining grouting hole spacing and ensuring curtain closure. It is governed by the coupled influence of multiple factors, including slurry properties, grouting pressure and duration, stratum permeability, ground stress, water pressure, and temperature. Engineering design commonly adopts reference values derived from coal mine kilometer-level shaft grouting specifications, wherein the effective diffusion radius of single-component cement slurry generally ranges from 4 to 6 m, while that of clay-cement slurry ranges from 8 to 12 m (Ministry of Housing and Urban-Rural Development [MOHURD], 2022). In practical engineering applications, these values are adjusted based on specific stratum conditions and grouting pressure to ensure effective grouting curtain closure. Following grouting reinforcement, a “slurry-rock (soil) composite” structure is formed, whose macroscopic mechanical behavior is influenced by factors such as the spatial distribution of slurry veins, the mechanical properties of hardened cement, rock mass characteristics, and the surrounding geological environment. Engineering practice
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