Multiscale study of the strength deterioration and microstructure changes in loess during dry‒wet and freeze‒thaw cycles

To study the influence of climate and the environment on the stability of loess slopes in Yan'an, China, the macromechanical deterioration and changes in its internal structure were explored by simulating its behavior during drying, wetting, freezing and thawing under natural conditions. A triaxial apparatus was used to conduct multiple shear tests to obtain stress‒strain relationships and shear strength parameters of the soil under different cycle modes, and the results were applied to analyze the macromechanical changes of the loess samples with increasing numbers of cycles. The results of the stress‒strain curves and the trends of the shear strength parameters showed that when a sample experienced coupled dry‒wet and freeze‒thaw cycles, its shear strength was considerably lower than that under a single type of cycle. Additionally, dry‒wet cycles had a stronger negative effect than freeze‒thaw cycles on soil strength. Microscopic tests showed that the contact mode of particles tended to be unstable due to the effects of dry‒wet and freeze‒thaw cycles, resulting in the reduction of soil cementation. The results of this multiscale research provide a reference for future work on geological disaster prevention and engineering control in areas where loess is present.