Abstract: Seasonal freeze-thaw conditions are one of the key factors exacerbating the mechanical strength decay of excavated and unloaded rock on reservoir banks in cold regions. In order to study the effective mechanical properties of an excavated unloaded rock mass on a bank slope under freeze-thaw action, triaxial unloading tests were carried out on sandstone, freeze-thaw cycling tests were carried out to simulate freezing strength, and triaxial creep tests were carried out on unloaded specimens subjected to freeze-thaw action using graded incremental loading. The results show that the overall deformation of unloaded specimens is significantly higher than that of conventional specimens, and creep is more likely to occur in the lateral direction than in the axial direction; the level of envelope pressure determines the level of creep deformation of unloaded specimens and affects the variation pattern of creep rate; the freezing and thawing exacerbate the creep behavior of unloaded specimens, and the longer the freezing period, the greater the percentage of creep strain and the creep rate increases significantly; the unloaded specimens subjected to freezing and thawing are mainly characterized by shear damage, and the creep process exacerbates the derivation of tensile cracks. The creep damage is mainly in the form of shear damage, and the creep process intensifies the derivation of tensile cracks in the specimens; the higher the peritectic pressure of the unloaded specimens, the more plastic and less brittle the creep damage is. The freeze-thaw action significantly reduce the long-term strength of the unloaded specimens, which is about 55% of the instantaneous strength, and the long-term strength decreases significantly with the increase of freeze-thaw cycle and has a lower threshold value. The results of the research can provide a theoretical reference for the evaluation of the long-term stability of unloaded rock masses in excavations on cold slopes.

Key words: cold area slopes, unloaded rock mass, freeze-thaw action, unloading test, creep properties