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Modeling the Swelling Curve for Packed Soil Aggregates Using the Pedostructure Concept

^a Institut de Recherche pour le Développement (IRD), Pôle de Recherche Agronomique de la Martinique, BP 214, F-97283 Le Lamentin, Martinique, France
^b Agric. and Biological Engineering, Purdue Univ., West Lafayette, IN 47906, USA

View larger version (36K): [in a new window]   Fig. 1. Schematic representation of the pedostruture composed of primary peds and primary particles.

View larger version (31K): [in a new window]   Fig. 2. Various configurations of air and water partitioning into the two pore systems, inter and intra primary peds, related to the shrinkage phases of a standard Shrinkage Curve. The polygon lines (1), (2), ..., represent the assumed swelling path steps of a bed of packed soil aggregates which is smoothly immersed in the water under conditions described in the article. The various water pools, wre, wbs, wst, wip, are represented with their domain of variation. The linear and curvilinear shrinkage phases are delimited by the transition points (A, B, C, D, E, and F). Points N', M', and L' are the intersection points of the tangents at those linear phases of the SC.

View larger version (17K): [in a new window]   Fig. 3. Graphs representing the water suction in macropore, hma (gray dots), the swelling pressure in primary peds Psmi (black line), and the cohesive pressure on the primary peds, Pc. The hma curves are measured tensiometric curves given in Braudeau and Mohtar (2004) for two soil samples of this study, and the Psmi curves are modeled according to Psmi = w Emi/wbs (Eq. [7]).

View larger version (32K): [in a new window]   Fig. 4. Apparatus and procedure for the continuous measurements of swelling for a reconstructed soil sample immersed in water followed by shrinkage and evaporation (weight) measurements during air drying.

View larger version (16K): [in a new window]   Fig. 5. Comparison between the different measurements of the structural parameters required for the swelling curve equation: a) water contents at particular points of the shrinkage curve, WN, WM, WL, and b) the slope of the basic shrinkage phase Kbs. Parameters of the non altered soil core sample replication are put on the X-axis while on Y-axis are reported the measurements of the reconstructed aggregated soil corresponding to the shrinkage curves of the two cycles R1 and R2.

View larger version (20K): [in a new window]   Fig. 6. Sample results of continuous measurements of two swelling-shrinkage cycles for T140 soil.

View larger version (23K): [in a new window]   Fig. 7. a) Swelling curves of two successive swelling-shrinking cycles of the T140 soil sample; dark dots represent the modeled swelling curve and the gray circles are the measured data. b) The corresponding linear regression according to Eq. [16] to determine the coefficient A = wkmiEmi/(WM – WN)2; circles are the measured data.