Hydraulic connectivity of water-rich strata and directional drilling grouting for deep tunnel

Aiming at the ambiguous hydraulic connectivity of water-rich strata and the technical challenges of water inrush control during deep tunnel construction, this study integrates field tests and theoretical modeling to investigate the hydraulic conduction characteristics of bedrock, the permeability properties of surrounding rock, and the associated grouting mechanisms and prevention technologies. The main findings are as follows. A wireless monitoring system for deep borehole hydraulic connectivity was established to characterize hydraulic conduction behavior at varying depths. Monitoring results reveal favorable hydraulic connectivity between shallow and deep strata, with a water head difference of only 0.3 m. A segmented pressure gauge installation scheme for single boreholes was proposed to eliminate leakage-related defects inherent in conventional testing methods. Field measurements indicate that the maximum permeability of the surrounding rock is 5.30×10^-7 m/s, corresponding to weak permeability. Seepage pressure increases with borehole depth, reaching a peak value of 0.24 MPa at a depth of 5.5 m. Based on the Bingham fluid diffusion model, a nonlinear relationship was identified between the rock mass permeability coefficient and grouting diffusion radius, whereas grouting pressure exhibits an approximately linear correlation with slurry diffusion range under fixed geological conditions. Considering in-situ stress and rock strength, the critical grouting pressure for rock failure was determined, and the maximum allowable grouting pressure was set at 8.0 MPa. In line with the proactive disaster prevention philosophy for tunnel engineering, a surface advanced directional drilling and grouting technique was proposed and validated using hydraulic connectivity data. Four grouting holes were arranged within a 7 m radius and 2.5 m from the tunnel contour. The water head at the monitoring point located 70 m from the tunnel axis increased by 4%, demonstrating the reliable water-blocking performance of the proposed method. This research enhances the understanding of groundwater evolution in tunneling environments and offers a novel technical approach for preventing water and mud inrush hazards in water-rich strata.