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.