Complex environment field in high and cold regions is an important factor for the deterioration of foundation soils, particularly leading to the serious damage of expansive soil canals. Therefore, this study aims to explore the effects of the freezing-thawing process among coupled wetting-drying-freezing-thawing cycles on the mechanical properties of canal foundation soils in cold regions. The expansive soil was also taken from the construction field in Northern Xinjiang, China. Firstly, the coupled wetting-drying-freezing-thawing and cyclic wetting-drying were performed on the expansive soils. A tri-axial consolidation drained shear test was then conducted below the canal structures. The variation characteristics were determined, including the stress-strain relationship, elastic modulus, failure strength, cohesion, and internal friction angel angle of expansive soils below the canal structures in the wetting-drying, and coupled wetting-drying-freezing-thawing cycles. The test results showed that the stress-strain relationship of expansive soils below the canal structures presented from general to weak hardening type (weak softening type), as the increase of wetting-drying and coupled wetting-drying-freezing-thawing cycles. It infers that the freezing-thawing in the coupled wetting-drying-freezing-thawing cycles significantly accelerated the development of transformation. Meanwhile, there was a significant decrease in the elastic modulus, failure strength, and cohesion of expansive soils below the canal structures at the beginning of coupled wetting-drying-freezing-thawing cycles. The decreasing trend was then gradually weakened, with the increase of cycles. Specifically, the elastic modulus, failure strength, cohesion, and internal friction angle of expansive soils below the canal structures decreased by about 13.1%-33.3, 21.2%-27.6,% 39.1%, and 15.6%, respectively, after 7 wetting-drying cycles, lower than the attenuation amplitude of 22.3%-34.5%, 22.2%-30.9%, 44.0%, and 11.7%, respectively, after 7 coupled wetting-drying-freezing-thawing cycles. It indicated that the freezing-thawing strengthen the attenuation of mechanical properties of expansive soils below the canal structures, but there was little effect on the internal friction angle. In addition, there was much more obvious damage of expansive soil under a low confining pressure. Since the damage was normally characterized by the traditional parameter of elastic modulus, there was an underestimated damage level of expansive soils below the canal structures subjected to wetting-drying and coupled wetting-drying-freezing-thawing cycles. As a result, a suggestion was made to consider the failure strength attenuation of expansive soils below the canal structures in high and cold regions. The findings can provide a sound scientific basis for the construction and maintenance of water delivery projects in Northern Xinjiang, China. © 2021, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
