Hydraulic conductivity of the matric porosity of an unsaturated vertisol: a field and laboratory comparison

Abstract

In many swelling clay soils several types of porosity can be defined: matric, structural and crack porosities. Measuring the hydraulic conductivity associated with the matric porosity is of major interest because soil movements are governed by matric water flows. Our purpose was to determine the matric conductivity of a vertisol from Guadeloupe (French West Indies) under laboratory and field conditions. We used an Eulerian flow description to measure the conductivity of natural vertisol clods in the laboratory with a drying method. In order to take into account soil movements in every direction, we introduced a tensorial analysis of soil deformations and hydraulic conductivity. The instantaneous profile method was used in the field under wetting conditions. Using soil layer thickness transducers we described water flows in a material coordinate system that can deal with volumetric soil deformations. For wet soil the ratio between the hydraulic conductivity measured in the field and that measured at the laboratory was around 10. However, because the spatial variation of the water content was large, no final conclusion could be drawn to explain this discrepancy. We showed that the gradient of the overburden potential was smaller than that of the matric potential in the field experiment.

Combined effect of interblock and interaggregate capillary cracks on the hydraulic conductivity of swelling clay soils

“…The reliable prediction of the hydraulic properties of deformable (swelling) soils is important for the development of actions connected to environment protection and water management and is a difficult problem even if cracks are absent [ Garnier et al , 1997a, 1997b, 1998; Ruy and Cabidoche , 1998; Askar and Jin , 2000]. However the hydraulic conductivity of swelling clay soils actually contains contributions of both soil matrix and cracks.…”

Numerical modelling of water infiltration into the three components of porosity of a vertisol from Guadeloupe

“…We suppose that the potential of water in the structural porosity is a linear function of the saturation of this porosity: struc is equal to 0 cm when the structural porosity is saturated and is equal to ae when it is air filled, where ae is the soil water potential at the CAE point (Ruy, 1997). The overburden component of the total potential of water (Philip, 1969) is not accounted for (Ruy & Cabidoche, 1998).…”

“…The method of was used to measure the first set of parameters, which are: the specific volume of solids, the specific volume of air and the matric WC at the crack air entry point. The second set of parameters (the water retention curve, the shrinkage curve, and the matric hydraulic conductivity) was measured according to the methods described in Ruy & Cabidoche (1998). The anisotropy ratio k was calculated from in situ measurements of vertical and horizontal soil movements (Ruy, 1997).…”

Mixture theory and unsaturated flow in swelling soils

“…About the same time, Philip (1969) presented his classical one-dimensional analysis of the problem, which was later improved upon by Sposito (1975). Following the publication of these articles, a number of other onedimensional studies rapidly began to appear (Smiles 1995, 2000, Narasimhan and Witherspoon 1978, Kim et al 1992a,b, 1993, Greco 2002, Wells et al 2003, Askar and Jin 2000, Ruy and Cabidoche 1998, Ruy et al 1999, Booltink 1994. Although these approaches are not mixture theoretic, but many of the results can be obtained using mixture theory.…”