Mechanical characteristics and load transfer mechanism of grout-rock dual media in penetrative fracture grouting

Grouting is a primary technique for enhancing the stability of fractured rock masses, and the load-transfer mechanism at the grout-rock interface significantly influences the failure of grouted rock masses. To investigate the load-bearing and load-transfer mechanisms in grouted rock masses with through-going fractures, artificial rock-like specimens containing fractures at various angles were prepared. After grout filling, uniaxial compression tests were conducted. Combined with discrete element numerical simulation, the influence of fracture inclination angle on the mechanical properties, failure modes, crack evolution, and load-transfer behavior of the specimens was studied. The load-transfer mechanism of the grout-rock dual medium was revealed through the analysis of macro-meso-scale structural changes in the grout body. Experimental and numerical results indicate:The strength of specimens with grouted through-going fractures is lower than that of intact specimens. Peak strength initially decreases and then increases with increasing fracture angle. At the grout-rock interface, normal stress progressively declines while shear stress increases. 45° is the critical angle threshold for changes in mechanical behavior, where specimen degradation is most severe, and normal and shear stresses reach equilibrium. Specimens with angles between 45°−75° exhibit significantly increased pre-peak strain and post-peak ductility. Intact specimens fail via splitting along both sides. Failure modes of fractured specimens are highly angle-dependent: For 0°−45°, failure manifests as flexural deformation with combined shear-splitting failure; bending occurs at the grout-rock interface, and cracks concentrate mainly in the upper-middle section. For 60°−90°, tensile-shear cracks in the specimen gradually converge toward both sides of the grout body, exhibiting a tensile-shear failure mode. A dynamic transition in the load-transfer mechanism of the grout-rock dual medium correlates with fracture angle. Taking 45° as the critical angle, the specimen structure shifts from an configuration centered on the grout to a configuration. In the former, the stronger central grout inhibits downward crack propagation, leading to a predominantly upper load-bearing structure. In the latter, both left and right structures contribute to load-bearing. As the angle approaches 90°, the influence of the grout on load transfer diminishes, resulting in more balanced crack distribution.This research provides a scientific basis for the design of grouting engineering under complex geological conditions.