Abstract:

Transversely isotropic loess undergoes dehumidification and shrinkage when subjected to vertical stress, resulting in changes to its water-retention characteristics and mechanical behavior. Improper management of this phenomenon can lead to substantial engineering losses. However, no theoretical models have been reported that investigate the impact of dehumidification and shrinkage on water-retention characteristics under vertical stress. This study utilized a pressure plate apparatus to perform soil-water characteristic curve (SWCC) tests on transversely isotropic loess with different initial dry densities. Water content w and volumetric changes were measured after stabilization at each suction level. The results indicate that, except for soil samples with lower initial dry density, the θ-s (θ is volumetric water content) curve displayed a slight upward trend under high vertical stress and low suction, while the water content of other samples generally decreased with increasing suction. During the suction increase, except for soil samples with very low initial dry density, the SWCCs of samples with the same initial dry density but different vertical stresses intersected. As suction increases to a certain value, higher vertical stress results in larger values of w, θ, and saturation S_r for the soil sample. Soil samples with higher initial dry densities exhibited reduced sensitivity to variations in vertical stress within their SWCCs. The volumetric strain of the soil sample increases with both increasing vertical stress and suction. By integrating generalized Hooke’s law with the Fredlund-Xing model, we established a volumetric strain model that accounts for coupled vertical stress-suction effects and a modified SWCC model for volume changes. Both models effectively captured the evolution of volumetric strain and saturation in transversely isotropic loess during dehumidification and shrinkage under varying vertical stresses. This research not only advances the theoretical framework of unsaturated soil SWCC models, but also offers critical insights for ensuring the safety of natural stratified foundations and compacted fill engineering projects.

Key words: transverse isotropy, unsaturated loess, volume change, water-holding characteristics, vertical stress