Effects of cyclic freezing and thawing on mechanical properties of Qinghai–Tibet clay

A fine-grained clay was compacted in the laboratory and was thereafter exposed to a maximum of 21 closed-system freezing and thawing cycles. The sample height, water content, stress–strain behavior, failure strength, elastic modulus, cohesion and friction angle were measured in initial unfrozen soil as well as in subsequent thawed soil. The results show that the physical–mechanical characteristic of investigated soils changed after it was subjected to freeze–thaw cycles. The height of sample increased and water content decreased before the sample exposed to 7–10th cycle of freeze–thaw, but both the height and water content remained constant after the 7th freeze–thaw. The shape of the stress–strain behavior curves were not affected by the freeze–thaw process, but the resilient modulus and the failure strength were heavily influenced by the number of freeze–thaw cycles. The minimal values for both the resilient modulus and the failure strength were frequently achieved after the specimen was exposed to about 3–7 freeze–thaw cycles, therefore, the resilient modulus and the failure strength of soils experienced seven freeze–thaw cycles could be applied to the process of cold region engineering design. For the soil investigated, the cohesion decreased with the increasing number of freeze–thaw cycles, and the friction angle exhibit an increasing trend.