Abstract: In order to study the mechanical loading and unloading properties of rock after freezing-thawing damage,we carried out loading-unloading test on sandstone of two different moisture contents under different freezing-thawing cycles. The results show that sandstone was damaged under the action of loading and unloading after freezing and thawing. The crack propagation direction changed,and the development of cracks intensified, especially obvous in saturated sandstones. From the point of view of the crack propagation direction and the fracture surface angle,the sandstone was dominated by shear failure under loading condition and tensile and shear failure under unloading condition. The damage caused by freezing and thawing indicated that the loss of peak strength and elastic modulus of sandstone increased gradually, which was slightly larger in saturated sandstone than that in natural sandstone under loading condition. Under unloading condition,the variation regularities of the unloading deformation modulus and the unloading equivalent of sandstone with different cycle times were basically consistent. The deformation modulus decreased significantly when the unloading equivalent was about 80%. The unloading deformation modulus decreased with the increase of the freeze-thawing cycle times while unloading equivalent remained unchanged. In addition,the unloading rate was so small in this paper that the influence on the deformation modulus was not obvious. The test results provide reference for the excavation of rock slope in cold region.

Key words: sandstone, freeze-thaw cycles, loading and unloading tests, unloading equivalent, deformation modulus, unloading rate