In-situ Waste Characterisation For Primary Settlement Assessment For High Embankment Built Over Municipal Solid Waste

Due to land restriction, some sections of several highway and railway projects have to be constructed over poor and uncommon foundation such as waste materials placed as part of the preceding landfill operation. Waste/Municipal Solid Waste (MSW) materials especially those comprising high amount of organic and readily degradable materials are highly compressible and have high variability in composition and void distribution. Conventional geotechnical laboratory testing and limited in-situ testing are often insufficient to characterise waste material. A design of field trial to understand the settlement characteristics will also require a reasonable understanding of the properties of waste materials.

This paper presents a basic methodology for in-situ characterisation of waste materials to enable the assessment of geotechnical properties of these materials on the basis of their composition and organic content. This includes the selection of suitable drilling method to allow for a good quality and continuous waste sample recovery. From such characterisation, a dimensionless Waste Compressibility Index (WCI) can then be derived based on procedures given in the published literature. The WCI value can then be correlated with compression ratio used to analyse primary consolidation settlement.

A case study is presented in this paper where a railway embankment was to be built over a landfill foundation consisting of existing Municipal Solid Waste (MSW) in the east coast of Australia. The foundation was treated by means of high surcharge. The abovementioned methodology has been used in the design to characterise MSW materials and assess primary settlements. The back-analysis by using settlement monitoring data indicate a reasonable agreement between the WCI related to the back-analysed compression ratio and the estimated WCI values. This agreement was obtained despite the variability in the aforementioned correlation. It shows that a basic methodology for in-situ waste characterisation on the recovered waste sample was able to provide a reasonable estimate of compressibility parameters for the purpose of analysing primary settlements.