Abstract: According to the special environment in deep seasonal permafrost regions, the repeated frost heave and thaw settlement properties of silty sand under different initial moisture contents, dry densities, overburden pressures, and freeze-thaw cycles were extensively investigated by means of laboratory experiments. Testing results show that: the freezing temperature is -1.03 °C. The deformation of frost heave and thaw settlement presents waves of ups and downs and then levels off in freeze-thaw cycles. Samples with higher dry density present expansion, while samples with lower dry density present compaction after repeated freeze-thaw cycles. The overburden pressure restrains the amount of frost heave, while increasing the amount of thaw settlement. However, the overburden pressure reduces the frost heave ratio and thaw settlement coefficient in every freeze-thaw cycle. At the optimal value of initial water content, the height of sample does not change after repeated freeze-thaw cycles. Due to water supplying to the samples, the water contents of samples frozen and thawed in the open system are greater than the initial water content. The increases of dry density and overburden pressure effectively restrain the outside water supply. The frost heave ratio and thaw settlement coefficient in every freeze-thaw cycle levels off after 4 freeze-thaw cycles.

Key words: silty sand, freeze-thaw cycles, frost heave and thaw settlement, frost heave ratio, thaw settlement coefficient