State Key Laboratory of Frozen Soil Engineering, Beilu'He Observation and Research Station on Tibetan Plateau, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA; Department of Joint NMR Laboratory for Freeze-Thaw Processes in Soils of State Key Laboratory of Frozen Soil Engineering and Suzhou Niumag Analytical Instrument Corporation, Lanzhou 730000, China.
Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA.
Adv Colloid Interface Sci. 2021 Aug;294:102465. doi: 10.1016/j.cis.2021.102465. Epub 2021 Jun 9.
The physical behaviors of water in the interface are the fundamental to discovering the engineering properties and environmental effects of aqueous porous media (e.g., soils). The pore water pressure (PWP) is a key parameter to characterize the pore water state (PWS) and its phase transition in the micro interface. Traditionally, the water in the interface is frequently believed to be uniform, negative in pressure and tensile based on macroscopic tests and Gibbs interface model. However, the water in the interface is a non-uniform and compressible fluid (part of tensile and part of compressed), forming a spatial profile of density and PWP depending on its distance from the substrate interface. Herein, we introduced the static and dynamic theory methods of non-uniform water based on diffuse interface model to analyze non-uniform water state dynamics and water density and PWP. Based on the theory of non-uniform water, we gave a clear stress analysis on soil water and developed the concepts of PWS, PWP and matric potential in classical soil mechanics. In addition, the phase transition theory of non-uniform water is also examined. In nature, the generalized Clausius-Clapeyron equation (GCCE) is consistent with Clapeyron equation. Therefore, a unified interpretation is proposed to justify the use of GCCE to represent frozen soil water dynamics. Furthermore, the PWP description of non-uniform water can be well verified by some experiments focusing on property variations in the interface area, including the spatial water density profile and unfrozen water content variations with decreasing temperature and other factors. In turn, PWP spatial distribution of non-uniform water and its states can well explain some key phenomena on phase transition during ice or hydrate formation, including the discrepancies of phase transition under a wide range of conditions.
水在界面上的物理行为是发现含水多相介质（如土壤）工程特性和环境效应的基础。孔隙水压力 (PWP) 是描述微界面孔隙水状态 (PWS) 和相转变的关键参数。传统上，根据宏观测试和吉布斯界面模型，界面中的水通常被认为是均匀的、负压和拉伸的。然而，界面中的水是一种非均匀的可压缩流体（部分拉伸，部分压缩），根据其与基质界面的距离形成密度和 PWP 的空间分布。在此，我们介绍了基于弥散界面模型的非均匀水的静态和动态理论方法，以分析非均匀水状态动力学和水密度及 PWP。基于非均匀水理论，我们对土壤水进行了明确的应力分析，并在经典土力学中发展了 PWS、PWP 和基质势的概念。此外，还考察了非均匀水的相变理论。在自然界中，广义克劳修斯-克拉佩龙方程（GCCE）与克拉佩龙方程一致。因此，提出了一种统一的解释来证明 GCCE 可用于表示冻土水动力学。此外，非均匀水的 PWP 描述可以通过一些专注于界面区域特性变化的实验得到很好的验证，包括空间水密度分布和随温度降低等因素变化的未冻结水含量。反过来，非均匀水的 PWP 空间分布及其状态可以很好地解释冰或水合物形成过程中相变的一些关键现象，包括在广泛条件下相变的差异。
