Macro and meso scale damage characteristics of granite with rock bridges under freeze-thaw cycles and confining pressure

In response to the instability risks faced by fractured rock masses in cold regions under the coupled effects of freeze-thaw cycles and in-situ stress, this study focuses on granite with prefabricated rock bridges. By conducting freeze-thaw cycle tests and triaxial compression experiments, combined with real-time acoustic emission monitoring, mineral composition analysis, and microstructural observation, the macro meso scale damage mechanisms of granite containing rock bridges under the combined action of freeze-thaw and confining pressure are systematically revealed. The results are as follows: ①The freeze-thaw cycles leads to lattice damage of minerals such as feldspar and the propagation of micro-cracks at the boundaries of mineral particles. The evolution of rock damage exhibits a phased characteristic, with rapid accumulation in the initial stage and gradual stabilization in the later stage. ②With the increase of freeze-thaw cycles, the stress-strain curve exhibits repeated stress drops. The ring counts appears earlier and more densely, with a distribution that tends to be more dispersed. This indicates that the development of internal damage gradually slows down and becomes discontinuous, and the failure mode transitions from sudden to gradual ductility. ③For specimens with low fracture inclination angles, tensile failure at the fracture tip is predominant under a low number of freeze-thaw cycles, with the rock bridge remaining relatively intact. As the number of freeze-thaw cycles increases, the failure mode transitions to tensile-shear failure through the rock bridge. For specimens with high fracture inclination angles, the failure always penetrates through the rock bridge, and as the number of freeze-thaw cycles increases, the failure progresses to rhombic shear failure. ④The fracture inclination angle dominates the propagation direction of cracks. Confining pressure inhibits tensile fracture and delays the freeze-thaw deterioration effect. Freeze-thaw cycles promote the evolution of failure modes from a single shear plane to a complex conjugate shear network, significantly increasing the degree of fragmentation. These findings can provide a basis for stability assessment and disaster prevention for rock engineering in cold regions.