Edinburgh Napier University

  The modelling of infiltration and moisture movement within a porous medium requires information on the moisture retention and hydraulic conductivity properties. In this study, the unsaturated hydraulic behaviour of a compacted waste sample based on the composition of Lyndhurst Landfill site in Melbourne, Australia was investigated in laboratory. Two fundamental aim of the study were to establish the moisture retention characteristics of Municipal Solid Waste (MSW) sample and measure its unsaturated hydraulic conductivity.
In landfilled waste, the particle and pore size distribution, heterogeneity of waste composition and leachate chemistry complicate the determination of moisture retention and hydraulic conductivity. In this study the modification and use of a standard pressure plate apparatus was described which can be used establish moisture retention properties of samples of 230 mm in diameter. The experiments showed that the moisture retention characteristics of compacted waste sample were comparable to soils. It has been shown that water retention in waste is a function of its position relative to the phreatic surface, in other words, its hydraulic boundary conditions which will vary with elevation. Some difficulties and limitations of using this method were discussed.
As with conventional inert soils, laboratory determination of unsaturated hydraulic conductivity is difficult and recourse is often made to analytical methods as those presented by van Genuchten (1980). One aim of this study was to compare the unsaturated hydraulic conductivity of MSW obtained using Passioura' s (1976) onestep outflow test method with predictions using van Genuchten's model. Good agreement is observed between the predictive model and experimental method for unsaturated hydraulic conductivities at low moisture contents but there is poor agreement at high degrees of saturation. This latter discrepancy is attributed to the difficulty of measuring retention properties of large pores at low suctions and the applicability of the van Genuchten model to such a material. Results also suggest that dual porosity exists within waste.