Experimental assessment on the fatigue mechanical properties and fracturing mechanism of sandstone exposed to freeze-thaw treatment and cyclic uniaxial compression

The coupling problem of freeze-thaw (F-T) treatment and cyclic loading is extremely prominent for rock engineering in Tibetan Plateau, which has triggered many serious geotechnical engineering disasters. It is thus essential to systematically characterize the fatigue mechanism of rocks exposed to F-T treatment and cyclic loading. In this study, a series of cyclic uniaxial compression tests are conducted on sandstone subjected to 0, 10, 20, 30, 40 and 50 artificial F-T cycles to investigate the influence of F-T treatment on the fatigue mechanical properties of sandstone, regarding the fatigue deformation characteristics, energy evolution and coupled F-T-fatigue damage. Our testing results indicate that sandstone specimens exposed to higher F-T cycles are featured by larger irreversible strain and faster damage accumulation, leading to higher fatigue damage variable and lower fatigue life. By virtue of the digital image correlation (DIC) technique and scanning electron microscope (SEM), the progressive fatigue fracture process and the microscopic morphologies of fracture surfaces of the F-T treated sandstone specimens are revealed. During the cyclic loading process, the strain field in specimens uniformly distributes initially, and then it localizes continually with increasing cyclic number, triggering the eventual fatigue fracture. With increasing F-T cycles, the fatigue fracture of sandstone is more ductile and progressive. Moreover, the hidden linkage between microscopic fracture mechanism and macroscopic mechanical properties is further analyzed based on the test results. In addition, the microscopic fracture mechanism of F-T treated sandstone under cyclic loading and monotonic loading is also compared and discussed: the primary micro-mechanism causing the fatigue fracture of sandstone is the inter-granular (IG) fracture, while the micro-mechanism triggering the monotonic failure is the trans-granular (TG) fracture. • Investigated the influence of F-T treatment on fatigue mechanical properties of sandstone under cyclic uniaxial compression. • Revealed the progressive fracture process and microscopic morphologies of F-T treated sandstone under cyclic loading. • Analyzed the hidden linkage between micro-fracture mechanism and macro-mechanical properties of F-T treated sandstone.