Influence of Chemical Stabilisation on Permeability of Municipal Solid Wastes

There are a number of important challenges in redevelopment of closed landfill sites including high permeation, complexity in settlement behaviour, weak shear strength, gas emission as well as health and safety issues. This paper is a part of a thorough experimental study on chemically stabilised old landfill sites. The decomposed waste materials were collected from Bankstown landfill located in the south-west of Sydney. The samples were prepared by mixing MSW, with a mixture of fly ash–quicklime with a ratio of 3:1 in percentages of 5, 10, 15 and 20 of fly ash by dry weight of the MSW. Permeability of treated and untreated MSW samples has been estimated during consolidation of MSW specimens in an automated triaxial cell. According to the results, increasing the content of fly ash–quicklime in the MSW specimen reduced the coefficient of permeability, the coefficient of consolidation and the permeability change index (C_k). The coefficient of permeability for an untreated specimen was 6.2 × 10⁻⁸ m/s and this figure was reduced to 3.2 × 10⁻⁸ m/s in specimens mixed with 26 % fly ash–quicklime (under an average confining pressure of 250 kPa). Increasing the effective confining pressure up to the pre-consolidation pressure caused no significant change in the coefficient of permeability. However at higher pressures the reduction was tangible. It is found that the chemical stabilisation effectively reduces the permeability of the MSW layer. This reduction in the coefficient of permeability can be attributed to a reduction in the bleed channels and void spaces due to the conversion of soluble calcium hydroxide to cementitious compounds. It will be beneficial and effective in redevelopment of closed landfill sites incorporating chemical treatments. The outcomes of this study may facilitate the hydraulic properties of chemically treated closed landfill sites.