Modeling the Unfrozen Water Content of Frozen Soil Based on the Absorption Effects of Clay Surfaces

• Published in: Water resources research Vol. 56; no. 12
• Main Authors: Jin, Xiao, Yang, Wen, Gao, Xiaoqing, Zhao, Jian‐Qi, Li, Zhenchao, Jiang, Junxia
• Format: Journal Article
• Language: English
• Published: 01.12.2020
• Subjects: electrical double‐layer theory; soil freezing characteristic curve; unfrozen water content
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2020WR027482

Unfrozen water content significantly affects the thermal‐hydro‐mechanical characteristics of frozen soil. Currently, theoretical explanations for the presence of unfrozen water include capillary action, surface effects, adsorption forces, and the electrical double layer. However, the relationships between unfrozen water and these actions are not well explained, except for capillary forces. In addition, although frost heave experiments indicate that the electrical double‐layer solution on a clay particle contains the main portion of unfrozen water, the electrical double‐layer theory which produces a cation solution has not previously been used to calculate unfrozen water content. In this paper, it is assumed that the residual unfrozen water at very low temperatures (below −18°C) is held within the adsorption‐layer solution and that the remaining unfrozen water within the influence of surface effects is the cationic solution in the diffuse layer. Based on these assumptions, a theoretical model of unfrozen water is established with independent variables of temperature, specific surface area, and electrical double‐layer parameters. While the input parameters of the theoretical model are numerous and difficult to obtain, the theoretical model is simplified as a parametric model. Results of the parametric model are strongly consistent with experimental data within a certain temperature range, supporting the hypothetical conditions. The similarity in the underlying mathematical structure of the derived theoretical and parametric models to current semi‐empirical models further suggests that the surface effects of clay are the main causes of unfrozen water in frozen soil. Key Points The presence of unfrozen water is explained by surface effects, adsorption forces, and the nature of the electrical double‐layer solution The surface effects are defined as the combined actions of molecules and negative charges on the clay surface The residual unfrozen water is a stable adsorption‐layer solution