Abstract: Freeze-thaw damage is a critical issue in engineering research in cold regions. Rock piles is a unique type of rock-soil mixture. To investigate the mechanical properties of rock piles in cold regions and the meso-scale damage induced by freeze–thaw erosion, the triaxial compression tests were conducted under varying water contents and freeze–thaw conditions. A pore damage increment model was proposed, and the particles (pores) and cracks analysis system (PCAS) method was employed to analyze the evolution of pore structure during the freeze–thaw process. Based on the fractal dimension of porosity, a freeze–thaw damage model was developed to systematically examine the relationship between freeze–thaw cycles and damage in rock piles. Combined with the variation patterns of meso- and macro-scale material parameters, the model’s rationality was verified and the damage mechanisms of rock piles under freeze–thaw action were elucidated. The results indicate that: (1) Meso-scale damage significantly affects macro-scale strength during freeze–thaw cycles. An increase in the pore increment parameter corresponds to a decrease in peak stress, indicating a negative correlation. (2) The peak stress of the rock pile decreases with increasing freeze–thaw cycles. The rate of decrease rises until approximately four cycles, after which the rate gradually declines. (3) The pore increment model, based on the fractal dimension of porosity, effectively confirms that freeze–thaw damage in rock piles increases with the number of cycles at the meso-scale. Model parameters show high consistency with measured data, and its calculations are simpler than those of traditional models.

Key words: rock piles, fine macro, pore damage increment model, fractal dimension, freeze-thaw damage