MEASUREMENT AND MODELING OF HYDRAULIC CHARACTERISTICS OF UNSATURATED POROUS-MEDIA WITH MIXED WETTABILITY

The spatial distribution of the solid grain's wettability strongly inf luences the phase-interconnection, phase-flow and solute transport in unsaturated porous media. Non-uniform wetting conditions can arise in soils and aquifers from natural or anthropogenic impacts. In this stud y, a water-air system in porous media consisting of several types of g ranular materials is considered. A conceptual model for pressure-wise estimation of water saturation and relative unsaturated hydraulic cond uctivity of such materials is proposed. The model uses the boundary wa ter retention curves and corresponding wetting angles of the pure comp onents of the mixture as the input parameters. The approach is based o n simplified statistical and geometrical assumptions for describing th e mixed porous material and its capillary behavior. In the experimenta l part of this study, three materials with different wetting angles (q uartz sand, silanized quartz and teflon grains) were used both as pure and as homogeneously mixed packings to conduct experiments with a wat er-air system in short columns under well-controlled laboratory condit ions. The hydraulic characteristics were determined for packings with various mixing ratios. The non-uniform matrix wettability was found to strongly influence the water retention behavior of the packings, wher eas its impact on the water-saturation-dependent hydraulic conductivit y was weak. The measured data are compared to model predictions. The r esults show that the model is capable of providing good qualitative es timates of both the boundary water retention curves and the curves of the relative hydraulic conductivity for all investigated materials. (C ) 1998 Elsevier Science B.V. All rights reserved.