The relation between the soil-water characteristic curve (SWCC) and the soil freezing characteristic curve (SFCC) is investigated based on the similarity between the freezing/thawing and drying/wetting behaviors of soils. The SWCCs of clay and silt are obtained by the pressure plate extractor and vapor pressure method, while the SFCCs are determined from the unfrozen water content measurement using the nuclear magnetic resonance (NMR) and temperature measurement. The pore water potential of the frozen soil is derived from a generalized Clapeyron equation, which addresses the effects of capillarity, sorption, and osmosis, and compared to that of unsaturated soils. Our experimental results show that at low water content the matric potential in the soil saturated with pore water and pore ice is generally different from that in the soil saturated with pore water and pore gas. A series of experiments on the soil samples saturated by NaCl solutions of different concentrations were performed to determine the osmotic potential and the water retention characteristics. Based on the principles of surface chemistry, a relationship between the adsorptive forces and the water film thickness is developed, which is capable of describing the soil water characteristic when the sorption effect is significant. Our results indicate that the freezing-point depression method should be applied with caution in determining the soil water retention characteristics of unsaturated soils at lower water content.

The pore-water status, including adsorptive and capillary water, in expansive clay with different dry densities was investigated under the effect of temperature and saline solution via the nuclear magnetic resonance technique. Combined with a method of distinguishing the adsorptive and capillary water, the variations in the adsorptive water content with the thermochemical effect were obtained quantitatively. The experimental results show that the adsorptive water content decreases as the temperature increases, consistent with the theoretical conclusion, which is considered to be attributed to the increase of the chemical potential and the activity of the pore water. On the other hand, the volume of micropores decreases while the volume of macropores increases with the increasing temperature or concentration, resulting from the flocculation and agglomeration of soil particles. Meanwhile, the increase of salt concentration can suppress the electric double layer and decrease the micropore volume, resulting in a decrease in the adsorptive water content. In addition, due to ion hydration, the relaxation of water molecules accelerates, shifting the water distribution curves of soil leftward as concentration increases. This effect overshadows the suppression of electric double layers and the decrease of the micropores, rendering higher adsorptive water content. The microstructure and the pore size distribution, obtained by the scanning electron microscope and mercury intrusion porosimetry experiments, were used to validate the variation of the adsorptive and capillary water in the pores.

Chalk shows a pronounced water-weakening effect, which can be attributed to the microscopic physicochemical interactions between the pore fluid and the chalk matrix. In this paper a conceptual elastoplastic model is developed for describing the chemo-mechanical behaviour of chalk based on the framework of the modified Cam Clay model. Central to the model is the concept of intergranular stresses, introduced as the substitute for Terzaghi's effective stress to describe the chalk behaviour. In this context, the microscopic physicochemical interactions are characterised by introducing a macroscopic surface force potential. The composition and significance of pore water pressure are analysed, and the intergranular stress tensor is explicitly defined. To address the hardening effect of the microscopic physicochemical interactions, the preconsolidation pressure function is modified by introducing the intrinsic intergranular pressure as an additional hardening variable that accounts solely for the chalk–fluid interaction. It is shown that the proposed concept of intergranular stresses can address the effects of osmosis, adsorption and capillarity on the chalk behaviour in a consistent and systematic way. Comparisons between the theoretical simulations and experimental results demonstrate that the proposed model is capable of capturing the main features of the chemo-mechanical behaviour of chalk saturated with an individual or two (miscible or immiscible) fluids.