Contribution of Osmotic Suction to Suction Stress for Unsaturated Saline Clay and Its Suction Stress Characteristic Curve

Abstract

The presence of water and salt transport in complex hydrochemical environments allows for continuous changes in the suction state of clay (matric suction, osmotic suction, and their interactions). The interaction between salt solution and negatively charged clay matrix alters the interparticle physicochemical forces, which makes the conventional suction stress theory for unsaturated soils not able to well characterize the local interparticle forces in unsaturated saline clays. For this reason, the relationship between osmotic pressure and osmotic suction of clay when the pores contain a general salt solution is first revealed from the concept of soil-water potential for the problem of macroscopic description of physicochemical forces in unsaturated saline clay. Subsequently, the suction stress formula for unsaturated saline clay is presented with the help of the mechanical analysis. The suction stress of unsaturated saline clay is divided into matric suction stress and osmotic suction stress, and its suction stress characteristic curve (SSCC) is analyzed. Finally, the extended suction stress theory is verified by utilizing the test results of the soil-water characteristic curve (SWCC) and shear tests for the four types of clays. The results indicate that the osmotic pressure of clay is affected by the clay’s type, osmotic suction, and stress level, so it is key to accurately consider the relationship between osmotic pressure and osmotic suction to describe the osmotic effect of saline clay. The presence of osmotic effects not only generates osmotic suction stress in clay but may also alter its matric suction stress, and the sum of these two components yields the total suction stress in unsaturated saline clays. From the verification, it is noted that the extended suction stress theory can effectively characterize the SSCC of unsaturated saline clay by solely increasing the surface fractal dimension. Additionally, this work provides a theoretical basis for explaining the mechanical behavior of unsaturated clay in response to hydrochemical environments.