Desiccation shrinkage of non‐clayey soils: multiphysics mechanisms and a microstructural model

Abstract

SUMMARYAnalysis of macroscopic desiccation shrinkage experiments indicates that most, but not all of the shrinkage during drying occurs while soil is still saturated. Shrinkage practically ceases and air starts to penetrate the soil, when the water content is still quite high, for example, above 20% for the tested soils. The remaining, unsaturated drying process occurs with a much‐reduced shrinkage rate. In this context, we examine data of the pore system evolution as represented by the mercury porosimetry experimental results. The process is then modeled as a two‐stage process of deformation and evacuation of a two‐tube vessel system driven by the external evaporation flux. In the first stage, Poiseuille flow occurs through the vessels. The amount of water evaporated in this stage equals to the reduction of volume of the vessel through the deformation of its walls. This stage ends when a negative water pressure (suction) required to further deform the vessel reaches a critical value at which air enters the pore space. Two physical interpretation of such threshold are discussed. In the subsequent stage, evaporation proceeds with a receding liquid/vapor interface starting from the open end, incrementally emptying the vessel but with a marginal water flow and vessel deformation. The leading variables of the process are identified, and a quantifiable multiphysics meso‐scale scenario of models is established. Copyright © 2012 John Wiley & Sons, Ltd.

Multi-Scale Approach for Modeling Desiccation Shrinkage in Granular Soils

“…In this context we examined (Hu et al, 2013a(Hu et al, , 2013b) microscopic data of the pore system evolution as represented by the mercury porosimetry results and postulated corresponding mechanisms based on the pressure (suction) development in the pore-vessels and ensuing water cavitation at a critical suction. The event of air entry plays a central role in the process of desiccation cracking; it is envision that it may signify the onset of desaturation stage.…”

“…A symmetric localized unstable mode of the interface evolution is observed. Hu et al (2013a;2013b) developed a meso-scale tubular model to simulate 1D shrinkage of drying silty soils, based on the Mercury Intrusion Porosimetry (MIP) results of evolution of the pore size distribution. Despite its geometric simplicity, it yields reasonable agreement with experimental observation of shrinkage characteristics of drying soils with different pore liquids (Hu et al 2013c).…”

“…The vapor flux applied at the pore-vessel end imposes the Poiseuille flow of water throughout the vessel, associated with the shrinkage of tubes, commensurate with the volume of water removed. Hu et al (2013a;2013b) established the formulation of viscous flow through a deformable single (straight) microscopic vessel in terms of the fluid pressure in the pore-vessel, p(x, t), based on Fung's equation for pressure vessel deformation (Fung 1984). This model is modified with a conventional linear elastic pressuredisplacement formulation (e.g., Hill 1950;Chen and Han 1988).…”

“…A parametric study would exemplify the complex nature of a drying and shrinkage process. The present study utilizes simple parameters discussed in Hu et al (2013a;2013b) and shows a sequence of desaturation development in different stages.…”

“…It should be noted that an approximate formulation for the interface movement is used. Hu et al (2013a;2013b) formulated a Stefan problem of moving boundary to account for the motion of the interface. The presented analysis simplified that equation by ignoring the small water pressure gradient, and arrives at a formula for the subsequent evolution of the liquid/gas interface, s,…”