Abstract:To study the evolution of physical properties and mechanical behavior of sandstone under different uniaxial stress-induced damage conditions and freeze-thaw cycles, firstly, different axial stress levels were applied to sandstone samples to produce different damage degrees. Then, the stress-induced damaged sandstone samples were treated by freeze-thaw cycles. Finally, uniaxial compression tests were carried out on the damaged sandstone. The effects of damage inside the samples and freeze-thaw cycle on the deformation characteristics of sandstone were studied. The evolution laws of uniaxial compressive strength and elastic modulus of sandstone with different damage degrees were analyzed. The evolution mechanism of porosity, pore size, and pore structure fractal dimension before and after freeze-thaw cycle was revealed. The results show that the axial deformation of the samples increases significantly under the same stress after freeze-thaw cycles. The uniaxial compressive strength and elastic modulus of sandstone decrease gradually with the increase of damage stress and the number of freeze-thaw cycles. Before and after the freeze-thaw cycles, the porosity of sandstone increases gradually with the increase of damage stress, and the porosity of sandstone after the freeze-thaw cycle is obviously larger than that before the freeze-thaw cycles. The difference of sandstone porosity before and after the freeze-thaw cycles increases as the damage stress increases. With the increase of the equivalent radius, the proportion of sandstone pore number before the freeze-thaw cycle can be divided into three stages: gradually decreasing, first increasing and then decreasing, and gradually decreasing. After the freeze-thaw cycles, the proportion of sandstone pore number gradually decreases, and the proportion of pores with larger equivalent radius increases after the freeze-thaw cycle. The fractal dimension of sandstone pore structure after freeze-thaw cycles is larger than that before freeze-thaw cycles. The pore structure of sandstone samples after freeze-thaw cycle is more complex than that of sandstone samples before freeze-thaw cycle. Before and after the freeze-thaw cycles, the fractal dimension of sandstone pore structure increases gradually with the increase of damage stress, but the increase amplitude of the fractal dimension of sandstone pore structure after the freeze-thaw cycles is obviously smaller than that before the freeze-thaw cycle.
