Abstract: Expansive soil channel in seasonal frozen region is easy to be affected by freeze-thaw cycles, so as to will affect its stability and safety. In order to explore the effect of freeze-thaw cycles on the physico-mechanical properties of expansive soil, Nanyang expansive soil is taken as an example, which is prepared with different water contents and then on which deformation measurement, unconfined compressive test and microstructure test are carried out after different freeze-thaw cycles. The results show that in the progress of freeze-thaw cycles, the volume change of expansive soil samples with low water content could be expressed as “frost shrinking and thaw expanding”, in contrast, the samples with high water content could be expressed as “frost expanding and thaw shrinking”. Freeze-thaw cycles affected heavily the stress-strain curve, strength and elastic modulus of expansive soil, especially the first freeze-thaw cycle. The higher the water content of the expansive soil sample is, the greater the degree of its mechanical parameters affected by freeze-thaw cycles is. The relationship between porosity and pore orientation and mechanical parameters of expansive soil samples is generally negatively correlated, which can be inferred that the change of microstructure of expansive soil affected its mechanical parameters directly in the progress of freeze-thaw cycles.

Key words: expansive soil, freeze-thaw cycles, volume change, stress-strain curve, strength, elastic modulus, microstructure parameters