Abstract:

To investigate the mesoscopic damage accumulation and the loading-induced fracture process in freeze-thawed rocks, a method coupling water-ice particle phase transition and expansion based on the discrete element method is proposed. The rock freeze-thaw process is simulated using a particle flow program, and the reliability of the simulation results is verified through laboratory experiments. The frost heave evaluation index λ_v of pore water particles is quantitatively characterized, and a functional relationship between λ_v and the number of freeze-thaw cycles N is established. Furthermore, the fracture characteristics and the evolution of microcrack, displacement field and force chain field in freeze-thawed rocks during the loading process are evaluated. The results show that: (1) The volumetric expansion of pore water in the rock and continuous water replenishment are the essential causes of rock damage under freeze-thaw treatments. Microcracks in the samples are dominated by tensile cracks during the freeze-thaw process, exhibiting an “initially slow, then fast” evolutionary trend, with more significant displacement of rock particles on the periphery than those in the interior. (2) The number of microcracks in the samples under loading exhibits a “slow→gradual→rapid” growth trend. The numbers of freeze-thaw cycles positively correlated with the number of microcracks but negatively correlated with the microcrack initiation stress σ_i . (3) The fracture process and morphology of the samples differ significantly before and after freeze-thaw treatment. When the load approaches the peak stress σ_f , there are “abnormal signals” in the microcrack distribution, displacement field and force chain field, which can serve as a precursor to failure identification. Under the influence of freeze-thaw cycles, the spatial arrangement of microcracks inside the samples becomes more complex, and the fracture mode transitions from dominance by tensile microcracks to dominance by mixed tensile-shear microcracks. This study provides a new idea and method for exploring the failure behavior of freeze-thawed rocks.

Key words: discrete element method, freeze-thaw cycles, particle flow, mesoscopic damage, uniaxial compression, fracture evolution