Abstract: Geotechnical projects in cold regions suffer from both cyclic freezing-thawing and excavation unloading, giving rise to rock degradation. In this article, the strength characteristics and damage characteristics of sandstone subjected to both cyclic freezing-thawing and excavation unloading are analyzed systematically by freeze-thaw cycle test and triaxial unloading test. The results are concluded as follows: in freeze-thaw cycle test, the sandstone experienced a stage from tension failure gradually to shear failure as confining pressure rises; as the freeze-thaw cycle proceeds, the sandstone witnessed an apparent lateral expansion in the middle, with different levels of tension cracks, circular cracks, rock powder and rock fragments; while in triaxial unloading test, as freezing-thawing proceeds, the peak strength of sandstone reduces, and dilatancy stress declines in an exponential relation; destructive confining pressure is in a quadratic functional relation with cycle number; moreover, the freeze-thaw damage value increases linearly with the number of freeze-thaw cycles, indicating that the effect of cyclic freezing and thawing intensifies gradually.

Key words: sandstone, freezing and thawing cycles, triaxial unloading test, strength characteristics, damage characteristics