INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS Int. J. Numer. Anal. Meth. Geomech. 2013; 37:1782–1800 Published online 9 July 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/nag.2107 Desiccation shrinkage of non-clayey soils: a numerical study Liang Bo Hu 1 , Hervé Péron 2 , Tomasz Hueckel 3, * ,† and Lyesse Laloui 2 1 Department of Civil Engineering, University of Toledo, Toledo, OH, U.S.A. 2 Laboratory of Soil Mechanics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 3 Department of Civil and Environmental Engineering, Duke University, Durham, NC, U.S.A. SUMMARY A mesoscale model of desiccation of soil based on the evolution of the pore system idealized as bimodal is numerically examined. A simplified evolution of the model reveals a series of characteristics that qualitatively agree with the observed macroscopic experimental findings. The principal mechanism is deemed to be driven by the surface evaporation and water outflow generating a pore pressure gradient resulting in the shrinkage mainly of the largest pores. The amount of shrinkage is a function of (negative) pore pressure and is controlled by the compressibility of the solid matrix. The numerical model includes also the ensuing partial saturation stage initiated by the air entry simulated as a scenario with a moving phase interface inside the pore. The proposed model can be extended beyond the two-mode porosity soils, to include the multi-modal porosity, or its statistical representation. Copyright © 2012 John Wiley & Sons, Ltd. Received 25 August 2011; Revised 16 April 2012; Accepted 26 April 2012 KEY WORDS: soils; desiccation; shrinkage; pore water cavitation; suction; porosity; simulation 1. INTRODUCTION Macroscopic desiccation shrinkage experiments on wet soils indicate that most of the drying shrinkage occurs while soil is still saturated [1]. Shrinkage practically stops simultaneously with the air entrance into the soil, when the water content is high (above 20% for the soils tested by the authors). The remaining drying process occurs with a much-reduced shrinkage rate, but almost entirely via desaturation [2–6]. Still, the specific mechanisms of shrinkage limit and air entry value are still not well understood. Hu et al. [7] (this Journal, this issue) have examined 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 vessels and a critical water pressure at the moment of air entry. The proposed model is based on macroscopic drying experiments [8–10], which indicate that at least two distinctly different stages develop in soils during drying, prior and post shrinkage limit, separated by the air entry. Physically, the pore system is represented by a two-vessel system, with the vessel diameters corresponding to two chosen principal mode pores. The first stage of drying consists in a Poiseuille flow of water in deformable pore vessels driven by the evaporation flux imposed at the boundaries (by the humidity difference). Air entry is interpreted either as a meniscus plunging or a subsurface cavitation in water, which are ‘physically indistinguishable’ phenomena [11]. The latter, implies reaching the tensile water stress equal to water tensile strength, which notoriously depends on the presence of dissolved air microbubbles or solid impurities in water. In the post air entry stage, evaporation proceeds according to a classical scenario of the receding liquid–vapor interface from the *Correspondence to: Tomasz Hueckel, Department of Civil and Environmental Engineering, Duke University, Durham, NC, U.S.A. † E-mail: hueckel@duke.edu Copyright © 2012 John Wiley & Sons, Ltd.