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DIVISION S-1—SOIL PHYSICS

Relationship between Clay Content, Clay Type, and Shrinkage Properties of Soil Samples

^a Lab. of Soil Science, Swiss Federal Institute for Technology, EPFL-ENAC-ISTE, 1015 Lausanne, Switzerland
^b INRA, rue Fernand Christ, 02000 Laon, France
^c Institut National de la Recherche Agronomique, Route de StCyr, 78026 Versailles Cedex, France

^* Corresponding author (pascal.boivin{at}epfl.ch).

The availability of methods for quasi-continuous measurements of soil shrinkage curves allowed the development of new models. The exponential (XP) model allows the calculation of the volume of two pore phases in the soil, namely macro and micropore volumes. The micropore volume is identified with the pore volume of the soil clay matrix according to the assumption that the maximum swelling of the clay matrix (MS) is the point of minimum water content of the structural shrinkage (Point D). This is discussed using undisturbed and repacked soil samples with various clay contents and clay types. The slope of the shrinkage curves as a function of equivalent saturated-pore radius show a transition in pore type around a 10-µm pore radius, where smaller and more deformable pores start to desaturate. This corresponds to the fitted D point and is close to the size of the largest pores in the clay matrix or clay–silt phase reported in the literature. The calculated micropore volume and micropore swelling properties are close to clay paste properties reported in the literature. At low water content, the specific micropore volume is independent from clay content. At Point D, the shrinking capacity of the specific micropore volume decreases with increasing clay content for clay contents below 40%. Our results show that Point D can be identified with the MS of the clay matrix, and that the XP model can be used to calculate the swelling properties of clays in the soil, without extraction.

Abbreviations: AE, air-entry point • LM, macroporosity limit • MS, maximum swelling point • SL, shrinkage limit • XP, exponential

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