Dynamic mechanical response and rupture mechanism of freeze-thawed jointed sandstones

Abstract

High-altitude cold regions are susceptible to the coupled effects of external freeze-thaw (F-T) and internal joints, leading to a series of rock-related disasters triggered by earthquakes and blasting activities. To investigate the dynamic mechanical response and rupture mechanisms of rock masses in cold regions, this study subjected intact, low-dip, couple-dip, and high-dip jointed specimens to cyclic F-T treatment, followed by dynamic loading using the split Hopkinson pressure bar system. A comprehensive discussion was conducted by integrating micro-parameters, multiple regression, and principal component analysis. The results indicate that F-T weathering accelerates the weakening of rock properties during later stages and lowers the energy threshold for failure, while rock masses containing high-dip joints can more readily meet the crack initiation conditions. In terms of energy, the utilization efficiency of sandstone is minimally impacted by F-T and joints, while the energy dissipation density exhibits a positive correlation with strain rate and a negative correlation with F-T cycles. Additionally, the digital image correlation technique was utilized to investigate the progressive rupture behavior of sandstone. Qualitatively, the technique elucidated the transition from brittleness to ductility induced by F-T cycles, as well as the shift from tensile to shear fracturing associated with joint geometries. Quantitatively, the analysis revealed a power-law acceleration pattern of high-strain areas prior to sandstone failure. Furthermore, on one hand, micro-damage analysis was employed to illustrate the synergistic deterioration of physical and mechanical properties in cold region rocks. On the other hand, a predictive model for dynamic strength was developed, revealing that fragmentation states are predominantly influenced by strain rate and secondarily by F-T damage. This overcomes the limitations of conventional methods that rely on single-parameter thresholds to distinguish failure modes. The present study establishes a comprehensive framework for evaluating dynamic instability mechanisms of jointed rocks in cold regions.