A Comparison of Experimental and Predicted Moisture Loss in Unsaturated Residual Soils Exposed to Relative Humidity Gradients

Abstract

The use of appropriate tortuosity factor in determining Dv (diffusion coefficient) leads to an accurate estimation of vapor fluxes from porous medium like soil. Tortuosity is the representation of interconnectedness of the pore space, and it accounts for the convoluted flow path traversed by the water (liquid/vapor) to diffuse into the atmosphere. As the soil desaturates into funicular and pendular regime from the saturated regime, reorganization of water takes place making the path less easy and more tortuous for its movement. Many researchers proposed several tortuosity models to predict the diffusive flux, but the applicability of a single tortuosity model (either as a function of volumetric air content/volumetric water content or an empirical value) for the entire suction range remains questionable. As the dominant mode of water transport (liquid and vapor) varies with desorption, the movement is dependent upon the interconnectedness of voids. Available relations to estimate τ based on idealized pore structure, porosity, and volumetric air content, led to large variations between experimental and predicted moisture vapor flux. A new simple relation based on experimentally derived data of a residual soil is proposed to predict τ from volumetric water content (θ).