Abstract: Freeze-thaw (FT) deformation accumulates in rocks in cold regions under cyclic FT conditions, adversely affecting engineering stability. Currently, understanding of cumulative FT deformation and its potential hazards in rocks is insufficient. Therefore, this study investigates the cumulative FT deformation characteristics of sandstone over multiple cycles and examines the effects of factors such as freezing temperature, cooling rate, saturation, and porosity through cyclic FT experiments. Optical microscopy, scanning electron microscopy, and mercury intrusion methods are used to analyze the distribution of micro pores, cracks, and pore sizes in sandstone before and after FT action, revealing the microscopic mechanism underlying macroscopic FT deformation characteristics of sandstone. Results indicate that the cumulative frost heave strain and residual strain in sandstone are significantly greater than those observed in the first cycle. Significant risk exists in cold region engineering response analysis based on single-cycle FT strain. Thus, using cumulative FT deformation as a basis is more reasonable. As freezing temperature decreases, cooling rate increases, or porosity increases, both cumulative frost heave strain and residual strain in sandstone increase. During FT cycles, micro pores and cracks in sandstone gradually develop, and connections between particles loosen. The internal pore structure changes, with a significant increase in the number of pores within certain pore size ranges. The total pore volume increases, resulting in irreversible plastic deformation. Consequently, macroscopic cumulative frost heave strain and residual strain increase gradually with the number of FT cycles.

Key words: sandstone, cumulative freeze-thaw deformation, multiple cycles, residual strain, microscopic mechanism