Mechanisms and critical properties in drying shrinkage of soils: experimental and numerical parametric studies

Mechanisms of free-shrinkage strains of desiccating deformable initially saturated soils are studied. The role of the surface evaporation rate, surface tension and viscosity of pore fluid, and soil compressibility and permeability is investigated in experimental and numerical parametric studies. Two different geomaterials with three different pore fluids are tested and numerically simulated using a macroscale Biot theory model and a mesoscale vessel model. Evolution of shrinkage strain and fluid content is reported and evaluated. The total amount of shrinkage and shrinkage limit are found to correlate with both solid fraction compressibility and surface tension of the fluid fraction. Most of the strain occurs in the saturated stage of drying concomitant with a build-up of fluid suction. The macroscopic Biot model yields good results in the saturated stage of drying. However, the air-entry criteria are all formulated at meso- or microscale. Hence, a mesoscale deformable pore vessel model is adopted, with pore fluid suction limited by a fluid tensile stress threshold identified with fluid cavitation. Beyond cavitation, air entry occurs. Subsequently, partially fluid-filled pore vessels are considered with fluid evaporation across a migrating fluid–gas interface within the vessel. A mesoscale model parametric study confirms that the total drying shrinkage strain and the shrinkage limit depend on the solids' compressibility, as well as on the fluid surface tension.