Improving Geotechnical Properties of Closed Landfills for Redevelopment Using Chemical Stabilization Techniques: A Case Study on Samples of a Landfill Site in Southwest of Sydney

Construction on closed landfill sites is generally a challenging task due to the complex behavior of creep, settlement, high amount of moisture content, and weak shear strength of waste materials. This chapter presents the experimental results and numerical analyses for the use of fly ash and quicklime in improvement of the geotechnical properties of municipal solid wastes (MSW). The waste materials were collected from a closed landfill in the southwest of Sydney. The samples were prepared by integrating 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. A series of experimental tests and numerical analysis were conducted on treated and untreated MSW samples. It was found that the chemical stabilization effectively increased the compressive strength, the shear strength parameters, the stiffness, and the brittleness index, whereas it decreased the settlement and the permeability of the MSW layer. The finite element program, PLAXIS version 9, was used to evaluate the settlement of a landfill model. The laboratory results were used to validate the numerical model. The settlement of the landfill model 10 and 20 years after the surcharge load was applied for different fly ash–quicklime contents and various depths of improvement was estimated. Results indicated that treatment of MSW significantly reduced the vertical displacement of the landfill model under surcharge load. This reduction was greater with higher depths of improvement.