Owing to the alternating processes of rainfall and evaporation, the compacted loess employed in ground and roadbed construction frequently experiences drying and wetting (D-W) cycles. These cycles are prone to induce substantial deformation of the soil mass, posing a risk to the integrity of buildings and infrastructure. Consequently, this study delved into the effects of D-W cycles on the deformation behavior of compacted loess, considering varying initial dry densities and water contents. To achieve a profound understanding of the deformation characteristics of the compacted loess, we meticulously monitored the resistivity ratio, crack ratio, and microstructure throughout the tests. Furthermore, a constitutive model was developed to forecast the deformation of compacted loess under D-W cycles. The findings revealed that both the vertical strain and crack ratio exhibited an upward trend with the increase in D-W cycle numbers, while they exhibited a downward trend as dry density increased. Notably, water content was identified as a significant factor affecting both the crack ratio and resistivity ratio. Additionally, the occurrence and progression of D-W cycles and cracks led to a slight increase in particle abundance and the proportion of total pore area. Meanwhile, during the wetting process, the infiltration of water softened the cementing substances, resulting in a disruption of the connections between aggregates. This made it much easier for cracks in the soil to expand after the sample dried. The constitutive model was meticulously constructed by incorporating yield surfaces that account for decreasing and increasing water contents. The validity of the proposed model was substantiated through a comparative analysis of the measured and calculated data. This comprehensive investigation furnishes a theoretical foundation for assessing the stability of compacted loess ground and roadbeds subjected to D-W cycles.

Existing constitutive models for unsaturated sand cannot capture the irreversible volumetric strain in the drying and wetting (DW) cycles. This study develops a novel hypoplastic model that aims to capture the behaviour of unsaturated soils, with a specific emphasis on the DW cycles experienced by unsaturated sand. The formulation integrates a hypoplastic model proposed by von Wolffersdorff for saturated sand with Bishop's effective stress. The simulation of soil water characteristic curve hysteresis is achieved through the implementation of the scanning rule for the main drying/wetting curve and scanning curve. The incorporation of a new tensorial term, Hs, into the hypoplastic equations, captures the irreversible volumetric strain in the DW cycle. A novel pyknotropy factor, referred to as fus, is proposed to replicate the rate at which irreversible volumetric strain accumulates during the DW cycle. Furthermore, the influence of suction effects on the critical state line is taken into account to represent the shear behaviour of unsaturated sand. The evaluation of the model performance is conducted through existing element tests on unsaturated sand. The comparison illustrates that the proposed model has the capability to capture certain essential characteristics, such as irreversible volumetric strain in the DW cycles and critical state behaviour of unsaturated sand. Due to its simplicity, the proposed model lends itself to straightforward implementation and potential utilization in future engineering applications, particularly in the analysis of slope stability in the presence of rainfall-induced conditions.