Physical and mechanical properties and damage mechanism of feldspathic sandstone with different moisture contents after freeze-thaw cycles

To study the mechanical response characteristics and damage mechanism of rock mass in cold-region freeze-thaw slopes, taking the feldspathic sandstone of a slope in an open-pit mine in Xinjiang as the research object, longitudinal wave velocity tests, uniaxial compression tests, and scanning electron microscope tests were adopted to explore physical and mechanical properties, macroscopic failure morphology of feldspathic sandstone and the meso-structural characteristics under different moisture contents and different numbers of freeze-thaw cycles. The study shows that: with the increase of moisture content and the number of freeze-thaw cycles, the damage longitudinal wave velocity of feldspathic sandstone samples gradually increases, the trend of the stress-strain curve gradually flattens, the uniaxial compressive strength decreases accordingly, the elastic modulus continuously decreases, and the degree of damage intensifies, meso-structural defects gradually develop. The peak strain of feldspathic sandstone first increases and then decreases with the increase of the number of freeze-thaw cycles, and the peak strain of feldspathic sandstone basically remains consistent under different moisture contents. The reason is that the frost heaving force caused by freeze-thaw cycles makes the internal structure of the rock loose, aggravates damage, declines mechanical properties, and enhances plastic deformation capacity. However, when the number of freeze-thaw cycles exceeds a certain critical value, large cracks dominate the failure process, and the brittleness of the rock is enhanced. Secondly, water has a weakening effect on minerals such as feldspar, and the lubricating effect of water leads to the weakening of the internal friction of the rock, the decline of rock mechanical properties, and greater damage degree.