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Modeling the Soil Shrinkage and Water Retention Curves with the Same Equations

^a Institute of Research for Development (IRD), LTHE, Universite J. Fourier, B.P. 53, 38041 Grenoble Cedex 9, France
^b INRA, rue Fernand Christ, 02000 Laon, France
^c Laboratoire d'étude des Transferts en Hydrologie et Environnement, LTHE, UMR 5564 (CNRS, INPG, IRD, UJF)- BP 53, 38041 Grenoble Cedex 9, France

View larger version (16K): [in a new window]   Fig. 1. Example of an experimental shrinkage curve (solid line) with the location of the transition points of the XP model: shrinkage limit (SL), air entry (AE), macroporosity limit (ML), and maximum swelling of plasma (MS), and the structural, basic, and residual shrinkage domains. Dashed line: theoretical 1:1 saturation line.

View larger version (28K): [in a new window]   Fig. 2. Examples of simultaneously measured shrinkage (ShC) and water retention (WRC) curves with the fitted XP equations, for Cambisols with (a) 17% and (b) 14% of clay, Vertisols with (c) 46% and (d) 51% of clay, and Fluvisols with (e) 8.5% and (f) 42% of clay. Abscissa: gravimetric water content W. Ordinates: specific bulk volume V (solid line), fitted XP model (dashed line), saturation line (dotted line) and suction h (black dots).

View larger version (13K): [in a new window]   Fig. 3. Calculated structural (KStr–triangle) and basic (KBs–square) slopes of the shrinkage curves as a function of swelling capacity (SC) for the whole set of data. Thirty repacked soil samples (open) and 28 undisturbed soil samples (black). F: Clayey fluvisol. V: Vertisol.

View larger version (27K): [in a new window]   Fig. 4. Examples of shrinkage (ShC) and water retention curves (WRC) measured simultaneously with the fitted VG equations, for Cambisols with (a) 17% and (b) 14% of clay, Vertisols with (c) 46% and (d) 51% of clay, and Fluvisols with (e) 8.5% and (f) 42% of clay. Abscissa: gravimetric water content W. Ordinates: specific bulk volume V (black solid line), fitted VG-modified equation (black dashed line), suction (gray solid line), and fitted VG equation (gray dashed line).

View larger version (18K): [in a new window]   Fig. 5. Examples of problems faced when fitting the VG modified equation on experimental shrinkage curves with linear phases, sloping ends, or dissymmetric parts. Experimental shrinkage (ShC) and water retention (WRC) curves (solid line), fitted VG modified and VG equations (bold dashed gray line) compared to fitted XP models (black dotted line) for sample C-15 (top) and sample F-17 (bottom) different from the ones presented before.

View larger version (20K): [in a new window]   Fig. 6. Examples of estimation of the water retention curve using shrinkage properties. Comparison between experimental data (solid line), direct fitting of the exponential model equations (dashed line), direct fitting of van Genuchten equation (gray dashed line), and estimation with the use of (i) macroporosity limit (ML) or maximum swelling (MS) water content fitted on the shrinkage curve, (ii) the slopes of the linear parts, and (iii) recorded suction at MS or ML (see prediction methods 2 and 3, Table 3, for the equations used). C-17 and C-14 are Cambisols, V-46 and V-51 are Vertisols, F-9 and F-42 are Fluvisols.

View larger version (17K): [in a new window]   Fig. 7. Relation between macroporosity limit (a) and maximum swelling (b) gravimetric water content values, fitted independently on shrinkage curve (abscissa) and water retention curve (ordinates), respectively, for the whole set of data: 30 repacked samples (open) and 28 undisturbed samples (black). Linear regressions are forced through the origin; R2 is the coefficient of determination.