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This paper presents the experimental validation of a macroscopic model of unsaturated flow in double-porosity soils, which was developed using the asymptotic homogenization method. The model was implemented into a code which enables micro--macro coupled calculations of macroscopically one-dimensional and microscopically three-dimensional problems. A series of drainage experiments were carried out in a column filled with a double porosity medium. The porous medium is composed of Hostun sand and porous spheres made of sintered clay, periodically distributed in the sand. The characteristic pores sizes of the two media differ by two orders of magnitude. During the experiments the water content evolution inside the column, the capillary pressure, and the flux at the bottom of the column were measured. The numerical simulations results showed a good agreement with the experimental data, confirming the predictive ability of the model. The experimental and numerical evidence of the influence of the microporous inclusions on the flow dynamics (flux retardation, water retention in the microporosity), is clearly shown. DOI: 10.1061/(ASCE)1090-0241(2008)134:2(231) CE Database subject headings: Unsaturated soils; Nonuniform flow; Drainage; Microstructure; Heterogeneity; Scale effect; Gamma rays; Model verification; Porous media.

Recent studies underlined the likeness of soil water retention (WRC) and shrinkage curves (ShC) with respect to their shapes. This paper aims at experimentally discussing the possible use of the same equations to fit them. The WRC (on the tensiometric range) and ShC were simultaneously determined on a series made of 28 undisturbed soil cores collected in surface horizons from a wide variety of soil types, with clay content ranging from 8.5 to 65% and of 30 repacked soil samples of various clay contents and mineralogies. The van Genuchten (VG) closed-form equation of WRC and the VG modified equation of ShC, with five and three parameters, respectively, were found to fit well to both curves, but they did not properly reproduce the observed linear parts and sloping ends of both curves, and the dissymmetric shapes of the ShC as well. The exponential shrinkage model XP fitted significantly better to both the WRC with five parameters and the ShC with eight parameters. It is shown that the transition points of the XP equations independently fitted on the ShC and WRC curves occur at the same gravimetric water content, thus illustrating the likeness of the curves with respect to their shape. The WRC was estimated with a reasonable accuracy from the water content of the ShC transition points plus some measured suction values.

The last years have seen the development of field methods that are capable of being applied to the direct measurement of simultaneous water and solute transport properties of soils. A tension disk infiltrometer was used to determine the ratio (f = [[Theta].sub.m]/[Theta]) between mobile water content ([[Theta].sub.m]) and the total volumetric water content ([Theta]) of a soil and to characterize the hydraulic properties. The soil is a heterogeneous stony soil of a cultivated plot, recently plowed. The hydraulic conductivity and the sorptivity were obtained using a new approach that considers the transient three-dimensional infiltration from a disk. The measurement of the mobile water content was performed by adding KCl tracer after prewetting the soil with water. Results show an important nonlinearity in both conductivity and sorptivity of the soil with applied pressure heads. The mobile water content ratio changes with the applied water pressure, and it was found to be a function of the effective mean pore size, [[Lambda].sub.m]. Results show a transition from a capillary-dominated to a gravity-dominated flow. The soil water flow changes to a macroporosity flow when the water pressure head increases from -100 to 0 mm, resulting in an abrupt increase in the mobile water content ratio from 0.11 to 0.37. The proposed f([[Lambda].sub.m]) relationship is an S-shaped analytical equation. It appears that for a given porous network topology, the mobile water content depends both on the dynamics of the water movement and on the connectivity of the porous network.

Batch and column experiments were conducted on a solute transport model integrating the leaching process and the adsorption-desorption process to study the relationship with time between H2SO4 consumption and Cu extraction. The rates of H2SO4 consumption and Cu extraction coincided, establishing the accuracy of the experiments. The consistency suggested the need for a second-order kinetic relationship for Cu dissolution and a first-order equilibrium isotherm for Cu to represent Cu recovery concentration at each column.

In Vandervaere et al. (2000) it was shown that the transient regime of axisymmetric infiltration can be described by a two-term equation with one term proportional to the square root of time and the other term proportional to time. The two corresponding coefficients, [C.sub.1] and [C.sub.2], are functions of the hydraulic conductivity, K, and the sorptivity, S. In this paper we propose four different methods to achieve the determination of S and K. The four methods differ by the number of disk radii and the number of supply pressure head values which are utilized. We show that the accuracy of a given method is highly dependent on the combination of S and K values obtained. Three situations can be distinguished, depending on the disk radius: (i) the flow is dominated by the lateral capillary term; (ii) the flow is dominated by the gravity term; (iii) lateral capillary and gravity terms have equivalent weights. The seven model soils tested here all correspond to the first situation with usual disk radius values. This tends to show that a precise estimation of K is unlikely from disk infiltrometer data. We introduce a new time scale, [t..sub.stab], which generalizes the concepts corresponding to the two well known time scales [t.sub.grav], and [t.sub.geom]. We propose a guideline for the investigator to choose between ali existing methods of analysis that use steady or transient flow. Finally, the four new methods are tested against numerically simulated tests with Grenoble sand and Yolo light clay.

Tension disk infiltrometer experiments are generally conducted until apparent steady state is reached because most of the methods of analysis are based on Wooding's solution for steady state flux. However, the time necessary to reach steady state may be a penalizing aspect for soils with low permeability and the information contained in the transient stages is not utilized. Moreover, these methods assume homogeneous soil and a uniform initial water content, which may be unrealistic when a large volume of soil is sampled, in this series, we propose and compare several new methods of analysis that are based on the transient stage of axisymmetric infiltration. In the first part, we show that a two-parameter equation--one term linear in square root of time and one term linear in time--adequately describes the transient flow from the disk infiltrometer for both simulated and laboratory tests. The technique used for the determination of the two coefficients must meet two criteria; it must verify the validity of the two-term equation throughout the duration of the experiment, and it must account for the early-time perturbation that is induced by the sand-contact layer placed between the disk and the soil. We show that the best technique consists in linearizing the data by differentiating cumulative infiltration with respect to the square root of time. Direct nonlinear fitting on cumulative infiltration or infiltration flux is likely to lead to unacceptable errors, either because of the undetected invalidity of the two-parameter equation or arising from the influence of the contact layer.

The article presents details regarding a controlled condition analysis on partitioning of evapotranspiration (ET) fluxes into soil evaporation and plant transpiration utilizing water stable isotopes. It reveals that it was possible, given the controlled conditions, to make partition without creating hypothesis of steady state transpiration. Moreover, it notes uncertainties related to the finding of partition values and isotopic composition measured in the field.