Wetting‐induced soil structural changes: The theory of liquid phase sintering

Abstract

Rapid wetting of structurally unstable soils causes aggregate disintegration and settlement near the soil surface, thereby reducing soil porosity and intake properties. Beneath the slaked surface layer where unsaturated flow conditions develop, structural changes driven mostly by capillary forces take place at slower rates. The collapse of structural voids in the sublayer is due to coalescence of aggregates into larger units. We propose to adopt a model of liquid phase sintering of glass compacts to describe wetting induced densification of aggregated soil. The analogy between these processes is based on the observations that (1) the reduction in soil strength upon wetting is similar to the effect of high temperatures on glass powders and (2) in both systems capillary forces induce viscous flow. A sintering model which assumes a porous medium with tractable geometry was modified to accommodate soil conditions. The model considers the reduction in the water‐coated solid surface areas (i.e., water‐air interfaces) as the energy source for the soil viscous flow. Data from wetting experiments of aggregated silt loam were used to test the plausibility of the theory. The main unknown in the system was the viscosity of wet soil which was estimated to be in the range of 1.37×106 to 1.9×106 Pa s−1. The use of solid matrix with tractable geometry and energy considerations should prove useful for other studies of the dynamics of soil structure.