Study on the influence of freeze-thaw cycles on the deformation and mechanical properties of expansive soil

In order to explore the influence of the severe weather in the seasonal freezing area on the expansion and contraction deformation and physical and mechanical properties of the canal base expansive soil with different water contents, the expansive soil in the Altay area of northern Xinjiang was taken as the research object, and the freeze-thaw cycle test of the actual climatic conditions in northern Xinjiang was performed in the laboratory. Based on this, the volumetric deformation test, unconfined compressive strength test and scanning electron microscope (SEM) test of the expansive soil with moisture contents of 12%, 16%, and 20% were carried out, and the influence of freeze-thaw cycles on the volume deformation and mechanical properties of expansive soil was analyzed emphatically. The results show that during the freeze-thaw cycle, with the increase of water content, the volume deformation of the sample changes from "freeze shrinkage and thaw expansion" to "freeze heave and thaw shrinkage". The characteristics of the stress-strain curve are closely related to the number of freeze-thaw cycles and the moisture content. The unconfined compressive strength of the sample decreases with the increase of the moisture content and the number of freeze-thaw cycles. Among them, the first freeze-thaw cycle is the most obvious, and it stabilizes after three times. The function fitting shows that the unconfined compressive strength of the sample has an obvious natural exponential relationship with the number of freeze-thaw cycles. The greater the water content, the greater the influence of freeze-thaw cycles on the microstructure of the soil; the porosity of the soil gradually increases with the increase in the number of freeze-thaw cycles. The first freeze-thaw cycle has obvious effect, which is manifested macroscopically as the effect of freeze-thaw cycles on the degradation of soil mechnical properties.