Abstract: To study the damage of sandstone in different hydration environment conditions after repeated freeze-thaw cycles, saturated freezing and thawing experiments were carried out on sandstone samples under the freezing temperature of ?30 ℃ and melting temperature of 30 ℃. The acoustic emission (AE) signals were recorded during each freezing-thawing cycle, and the microscopic characteristics of sandstone were investigated by low field nuclear magnetic resonance (NMR) and an optical microscope after every three cycles. The uniaxial compression test was conducted at the end of cycles. The results show that since 3% NaCl solution leads to the internal microstructure destruction, with increasing cycle index, the spectrum shifts to the right, the total area of spectrum and the porosity increase. The AE absolute energy probability density of sandstone still meets the power law distribution after freeze-thaw cycle under uniaxial compression, but the critical exponent increases and the increment of 3% NaCl is greater than that of distilled water. In addition, the critical exponent of AE probability density for each freezing and thawing cycle increases first and then decreases with increasing cycle number, which is similar to existing ultrasonic testing results. The peak of critical exponent in thawing process is higher than that in freezing process, which means that thawing process has shorter breaking time and a lower damage degree. The freeze-thaw damage is mainly caused by the static pressure, osmotic pressure destruction and dissolution but also the erosion of rock by hydration medium. This study can provide some references for understanding failure mechanism and stability evaluation of rock engineering in cold regions.

Key words: sandstone, freezing and thawing cycle, low filed NMR, acoustic emission, uniaxial compression, probability density function