Soil Sorptive Potential: Concept, Theory, and Verification

Abstract

Despite the widely accepted notion that water potential is the fundamental variable for describing soil–water interactions in soil under unsaturated conditions, it is unable to describe several basic soil properties and behaviors such as pore-water pressure, soil water density, and phase changes of soil water. A variable with greater explanatory power, sorptive potential, is conceptualized as the origin of matric potential and pore-water pressure. The sorptive potential is the sum of the locally varying electromagnetic potentials comprising van der Waals attraction, electrical double-layer repulsion, and surface and cation hydration. Local thermodynamic energy equilibrium dictates that the sorptive potential is always transformed or equal to matric potential minus the pressure potential within a representative elementary volume of matric potential. Limited verification was demonstrated by reducing the sorptive potential to the two well-established concepts of disjoining pressure and osmotic swelling pressure. A parametric study was conducted to illustrate how soil and pore-fluid properties affect sorptive and pressure potentials, indicating that the pore-water pressure under unsaturated conditions can be as high as 0.6 GPa. Such locally high pore-water pressure is induced by the sorptive potential and provides an explanation for phenomena such as abnormally high soil water density, supercooling, and decreased cavitation observed in fine-grained soils.