Soil Sorptive Potential: Concept, Theory, and Verification

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.