Mechanical Strength Decay Evaluation of Excavation Unloaded Rock Mass under Freeze-Thaw Conditions

The quality of excavated and unloaded rock masses on steep and high slopes in cold regions is prone to deterioration, which in turn affects the long-term stability and safety of excavated slopes. Based on a triaxial unloading-damage test of sandstone, the unloading quantity was used to analyze the evolution law of unloading damage; a freeze-thaw cycle test of the unloaded-damaged samples was carried out, and it was found that the average change in porosity and the reloading peak strength damage rate after freeze-thaw increased with the increase in the number of freeze-thaw cycles, and the porosity change characteristics were independent of the value of the confining pressure at the time of the unloading damage. An exponential decay model was used, and based on the average change in porosity after freeze-thaw, a freeze-thaw strength decay model that can take into account the effect of confining pressure was established, and its ability to predict the strength decay of unloaded-damaged rock samples after freeze-thaw was verified by experimental data. The research results provide a reference for the evaluation of freeze-thaw degradation of unloaded rock masses during slope excavation in cold regions.