Characterisation of municipal solid waste materials for the purpose of engineering design in transport infrastructure project

Space restriction especially in the urban area has contributed to the reuse of landfill area, where Municipal Solid Waste (MSW) is disposed, for the purpose of infrastructure development. This type of development presents some significant challenges in the engineering design due to high variability of MSW properties and the uncertainty in relation to the application of conventional geotechnical engineering principle for the engineering design involving MSW materials. MSW materials are highly variable not only in different landfill sites, but they also are likely to vary over the distance and depths within a landfill site. In addition, the engineering properties of MSW materials are influenced by a number of factors including the landfill age, constituents of landfill, placement method and the leachate recirculation. This variability along with a risk associated with the biological and chemical hazards arising from the direct exposure to the waste materials and toxic gas pose limitations in conventional (a) geotechnical site investigation and (b) laboratory testing of MSW. Therefore, characterisation of MSW for the engineering design needs to be carried out based on limited site specific information and published data. This paper presents a typical geotechnical investigation and characterisation of waste materials for the engineering design of a transport infrastructure considering the aforementioned limitations. A case study involving a proposed transport infrastructure over an active landfill site in NSW has been selected. A Geotechnical Site Investigation (SI) involving a sonic borehole drilling has been carried out with a primary objective of obtaining continuous samples for the observation of waste materials as opposed to the in-situ testing and drilling with poor recovery. In addition, test pit excavation and geophysical investigation have been carried out to gather more information to develop the geotechnical model. Various MSW materials recovered in the boreholes and test pits were thoroughly assessed on site during the SI to obtain the MSW composition including the proportion of each type of waste material using the method outlined in Landva and Clark (1990). This observation was then compared against the results of geophysical investigation. By using the outcome of SI, previous geotechnical investigation and settlement monitoring conducted about 30 years ago within the subject area and extensive published data on MSW properties including the Waste Compressibility Index, a comprehensive guide has been prepared to develop the design parameters for geotechnical design of the proposed rail embankment. This guide will be a useful tool for practicing engineers to develop geotechnical design parameters of landfill materials.