Assessing the role of the pore solution concentration on horizontal deformations in an unsaturated soil specimen during drying

Volume changes occurring in soil–water systems are the result of multi-scale interactions that affect several processes in the soil–water continuum. For example, the soilʹs shrinkage/swelling properties result in horizontal and vertical deformations at the soil specimen scale, and lead to cracking which is often responsible for producing preferential flow paths that impact the hydrologic response at the plot and field scales. In spite of their significance, a complete understanding of soilsʹ deformations and their corresponding impact on volume change behavior continues to be a major challenge. This paper presents an approach to quantify and interpret the role of the pore solution concentration on horizontal deformations of unsaturated soils. Specifically, a restrained ring method (RRM) is integrated with digital image correlation (DIC) techniques to relate the internal soil stress (caused due to drying) to the shrinkage strain (deformation) that develops in the soil specimen. The experimental results are described in the context of the theory of drying while explicitly considering the effect of changes in the properties of the pore solution (i.e., surface tension, viscosity and density) induced by the addition of a binary salt (NaCl). The experimental results conform to fundamental expectations and thereby this approach facilitates a better understanding of volume changes in unsaturated soils exposed to saline environments.