The role of effective pressure on fracture and failure mode mechanisms in freeze-thaw damaged rocks

Global climate change has increased the frequency and intensity of freeze-thaw cycles (FTCs) in high-altitude regions, progressively causing microstructural damage and significant deterioration of rock mechanical properties. Building upon our previous work, this study investigates the acoustic emission (AE) source mechanisms and fracture modes of Westerly granite under triaxial loading, using an improved freeze-thaw grain-based model (FT-GBM). The model incorporates a particle expansion method to simulate pore water and ice, effectively coupling discrete element method (DEM)-based FT simulation with triaxial loading and AE analysis, to examine degradation mechanisms of Westerly granite under cyclic FT conditions. Triaxial simulations under confining pressures ranging from 5 to 40 MPa reveal that increasing FTCs lead to progressive microcrack accumulation, whereas higher confining pressures promote more localized crack distributions. Tensile cracks predominantly develop within mineral grains, whereas shear cracks are mostly concentrated along grain boundaries. With an increasing number of FTCs, the granite exhibits reduced peak strength and increased peak strain, indicating a transition from brittle to ductile failure. These findings further validate the novel three-stage FT-induced damage framework. In this framework, partial saturation temporarily enhances structural integrity due to ice infilling in pore spaces. Following the damage initiation stage, frost-induced expansion causes severe structural degradation. AE analysis identifies compaction-type (C-type) events as critical precursors to dynamic failure, primarily concentrated near macroscopic fracture zones. These results underscore the predictive value of AE monitoring particularly the detection of C-type signals for identifying frost-induced damage in geotechnical applications in cold regions. The proposed FT-GBM model offers a refined predictive framework for understanding rock degradation under cyclic environmental stress and provides crucial insights into the resilience of infrastructure in cold climates. • Improved freeze-thaw grain-based DEM coupled with triaxial loading and AE. • Freeze-thaw cycles reduce strength and promote brittle ductile transition. • Confinement localizes cracks and shifts tensile to shear failure. • C-type AE events precede macroscopic shear fracture. • Three-stage freeze-thaw damage framework is validated.