Degradation characteristics of shear strength of joints in three rock types due to cyclic freezing and thawing

With massive engineering projects carried out in cold regions where freeze-thaw processes can affect the mechanical properties of rock material, the temporal variation of geotechnical stability is highly concerned. Three typical types of jointed rocks were selected to undergo a number of freeze-thaw cycles after which direct shear tests were conducted on samples of joints in the rock material. The degradation characteristics of the rock joints were examined by the changes of the shear parameters after increasing numbers of freeze-thaw cycles. The results show that the cohesion is more sensitive to cyclic freezing and thawing than the joint friction angle and that the influence on cohesion and joint friction angle is different between hard rocks and soft rocks. Based on the damage mechanics theory and the fact that the deterioration degree rises with increasing numbers of freeze-thaw cycles, the damage state variable was redefined to develop an exponential decay model of freeze-thaw cycles. The comparison of the fitting curves obtained by the proposed model with the experimental results shows that the model reasonably well reflects the degradation characteristics of the shear strength under cyclic freezing and thawing. The model can thus be used to predict the tendency of geotechnical strength degradation of rock masses in cold regions.