Collapsibility deterioration mechanism and evaluation of compacted loess with sodium sulfate under drying–wetting cycles

The deterioration of loess collapsibility under drying–wetting cycles is one of the serious threats to the artificial loess slopes and foundations in China, especially when soluble salt is involved. In this paper, a series of collapsibility tests were used to study the collapsibility deterioration of compacted loess with sodium sulfate under drying–wetting cycles, and the scanning electron microscope (SEM) tests were carried out to investigate the variation in microstructural properties. The results show gradual increase in the collapsibility of the loess samples with the increasing drying–wetting cycles and salt content. The collapsibility coefficient increases and gradually tends to stabilize with the progress of drying–wetting cycles, while changes linearly or exponentially with the salt content. The coupling effect of drying–wetting and salt erosion makes the loess skeleton looser and weaker in structure, providing more pore space for the deterioration of collapsibility, and when the salt content is greater than 0.5%, the deterioration ratio due to salt erosion is higher than that of drying–wetting. By fitting the collapsibility deterioration data with the hyperbolic function, the effect of drying–wetting cycles and salt content on the maximum and development speed of deterioration rate are quantitatively analyzed, and then, an interpolation equation of collapsibility deterioration considering both the influencing factors is established, which can well evaluate the collapsibility deterioration of compacted loess.