Filling characteristics of grout diffusion zone in fractured rock mass and its influence mechanism on rock mass strength

In this study, numerical experimentation was employed to investigate the influence mechanism of rock mass filling degree with rough cracks on the strength of the reformed rock mass. The diffusion pattern of slurry within rough cracks, characterized by JRC parameters, was analyzed. Uniaxial compression tests (UCS) and direct shear tests under normal phase stiffness (CNS) were conducted to examine different roughness and filling degrees of the reformed rock mass. A systematic research approach was established to investigate the correlation between slurry filling patterns and the strength of the reformed rock mass. The findings reveal that slurry flow within rough cracks exhibits layer/turbulent characteristics, while slurry within smooth cracks experiences reduced shear forces along the crack walls, facilitating laminar flow. Rough cracks dictate slurry flow, inducing eddy currents near the wall. The compressive strength of the reconstructed rock mass exhibits proportionality to the extent of fracture filling. The fully filled fissure plastic zone transitions gradually from a double X shape to a single X shape. Unfilled fissures lack effective constraints on their boundaries, resulting in a significant difference between the maximum and minimum principal stresses. After slurry solidification, the joint action of cohesion and space encroachment limits the relative sliding of the fracture boss, increasing the initial friction and contact area of the fracture, thereby enhancing the shear strength of the modified rock mass. Under the boundary conditions of CNS, the increase in shear strain leads to stress concentration growth and an increased rate of new micro-crack formation in the grouting body, aligning with the stress distribution characteristics of the internal micro-cracks. These findings provide a solid experimental basis for analyzing the diffusion patterns of slurry in fractured rock mass and the evolution of rock mass strength after reconstruction.