Hydraulic conductivity of gravelly soils with various coarse particle contents subjected to freeze–thaw cycles

•Hydraulic conductivity in a gravelly soil is experimentally investigated through triaxial permeability tests.•Effects of freeze-thaw cycles, gravel content, confining stress and initial compacted water content are incorporated.•A prominent increase of hydraulic conductivity upon freeze-thaw cycles occurs in gravelly soil samples compacted at the dry side of wopt.•The relationship between hydraulic conductivity and void ratio is estimated by an exponential function regardless of cyclic freezing-thawing. Gravelly soils, characterized by a mixture of fine soil matrix and coarse gravel aggregates, are widely distributed in high mountain and cold plateau areas. These soils are frequently subjected to freeze–thaw (F-T) actions, and the hydraulic conductivity is crucial for analyzing hydrological processes and geological hazards. This study aims to investigate hydraulic conductivity in gravelly soils containing various contents of gravel particle fraction under cyclic freezing–thawing. The results show that the hydraulic conductivity in gravelly soils significantly depends on gravel content, confining stress, number of F-T cycles and initial water content. The presence of gravel particles modifies the porosity and pore connectivity/tortuosity in soil matrix, as well as affects the soil matrix-gravel interfaces. With increasing gravel content, the overall gravel assembly transforms from a state of floating in the soil matrix to forming a contacted skeleton structure. Thus, the extensively developed loose soil-gravel interfaces due to F-T cycles result in a significant increase in hydraulic conductivity. Increasing confining pressure significantly reduces the soil matrix void ratio and thereby decreases the hydraulic conductivity, while no longer recovers the degradation in soil-gravel interfaces induced by F-T cycles. Different initial compacted water content provides different compacted soil structures, divided by the optimum water content (wopt). A prominent increase of hydraulic conductivity after F-T cycles occurs in samples compacted at the dry side of wopt, while a slighter increase at its wet side.