Mode II Fracture Properties and Microscopic Damage Characteristics of Granite Under Freeze–Thaw Cycles: Laboratory Testing

Abstract

Rock masses in alpine regions inevitably undergo freeze–thaw (F–T) cycles, which affects the safety of infrastructure such as slopes, with shear failure being a significant concern. This study investigates the Mode II fracture behavior of F–T treated granite via the short core in compression (SCC) test, analyzing the related physical properties and mechanical properties while also discussing F–T damage mechanism at a microscopic level. Results reveal that as F–T cycles increase, the dynamic elastic modulus and P-wave velocity decrease, whereas porosity and backbone fractal dimension of pore scale increase, indicating a transition towards a large-scale pore. Mode II fracture toughness decreased by 31.19% and fracture process zone width increased by 248.49% with F–T cycles rising from 0 to 80, and related fractal dimension of surface morphology also increased by 11.17%. Microscopic observation reveals the microstructure deterioration induced by F–T treatment, indicating the correlation between microscopic damage and macroscopic fracture properties.