Grouting-Induced Spatial Heterogeneity and Hydro-Mechanical Response of Fractured Rock Masses: Insights from Experimental Investigation

Grouted rock masses are rarely homogeneous due to heterogeneous grout transport, yet its effect on hydro-mechanical properties is unclear. This study conducted a single chamber-scale grouting experiment on fractured rock, from which 36 cylindrical specimens were obtained using a spatially distributed sampling scheme (vertical position, radial distance, and azimuth), followed by stress–permeability coupling tests. The results show a progressive transition from high-strength–low-permeability near the injection point (lower region) to low-strength–high-permeability in the upper far-field, with azimuthal variations. Peak strength decreased from 38.39 MPa to 23.69 MPa, while initial permeability increased from 0.20 × 10−17 to 0.58 × 10−17 m2. Peak strength shows a nonlinear negative correlation with initial permeability, but strength–permeability relationships vary across regions; similar strength levels can have different permeability, indicating that bearing capacity and water-blocking are governed by cemented skeleton and residual flow channels jointly. The pressure-response characteristics and SEM observations suggest that nonuniform grout transport and filling, local clogging, and possible flow-path redistribution contributed to the observed spatial heterogeneity. Continuous permeability monitoring of four selected specimens showed that the lower/near-injection specimen exhibited limited pre-peak permeability variation and slower post-peak softening, whereas the upper and far-field specimens showed greater permeability fluctuations and more pronounced softening. The results provide a spatial basis for identifying weakly reinforced regions and evaluating grouting performance in fractured water-bearing rock masses.