Experimental study on effect of freeze-thaw cycles on dynamic mode-? fracture properties and microscopic damage evolution of sandstone

The investigation of dynamic fracture characteristics of sandstone after freeze-thaw (F-T) treatments is of great significance for the optimization of blasting parameters and stability analysis of rock masses engineering in cold or high-elevation regions. In the present study, the P-wave velocity, porosity, T2 spectrum curve, and micromorphology of sandstone specimen after different F-T cycles were measured using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques. The F-T damage factor was defined according to the reduction in wave impedance. Moreover, the dynamic mode-? fracture test was carried out using notched semicircular bend (NSCB) sandstone specimen. Meanwhile, the fracture process of NSCB spec-imen was captured by adopting a high-speed photography system. Test results show that F-T cycles can irreversibly deteriorate the microscopic pore structure and the cementation between mineral particles, which is manifested by an increase in the proportion of macropores and mes-opores. The dynamic fracture pattern of sandstone specimen is affected by the coupling of F-T cycle number and loading pressure. Furthermore, the dynamic fracture toughness of sandstone constantly increases with the increase of loading rate at a specified F-T cycle number, while the F-T cycle treatment has a significant weakening effect. There has a negative exponential correlation between dynamic fracture toughness and F-T damage factor.