In order to study the effect of freeze-thaw cycles on the microstructure and dynamic mechanical properties of sandstone, nuclear magnetic resonance testing, electron microscope scanning and dynamic impact compression tests with impact velocities of 3, 6 and 9 m/s were carried out on sandstone with freeze-thaw cycles of 0, 30, 60, 90 and 120 times, respectively. The results show that the dynamic mechanical properties of sandstone deteriorate with the increase of freeze-thaw cycles at the same impact velocity. All dynamic mechanical properties have rate-dependent effects. In addition, the dynamic peak stress index attenuation model of freeze-thaw sandstone is established, and it is proved that the impact velocity can compensate the damage and deterioration of freeze-thaw cycle to a certain extent, which can reduce the attenuation constant and prolong the half-life of freeze-thaw sandstone. The dynamic impact failure mode of freeze-thaw sandstone is as a whole crushing failure. With the increase of freeze-thaw cycles and impact velocity, the fragmentation degree of sandstone increases, the fragment scale decreases, the fragment quantity and powder proportion increase, and the fractal dimension increases. Based on the above tests, the damage mechanism of sandstone under the action of freeze-thaw cycle is explored, and it is found that frost heave damage is the main cause of freeze-thaw damage of sandstone. With the increase of freeze-thaw cycles, the internal damage degree of sandstone intensifies, the bonding effect between mineral crystals and cementing materials weakens, the pore size and number increase, and even intergranular cracks and transgranular cracks appear. This study can provide relevant reference for rock engineering in cold area
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