Geotechnical characteristics and admixture stabilization of biosolids

Biosolids are defined as appropriately treated sewage sludge which consists of organic slurry residue derived from wastewater treatment processes. The sustainable usage of waste materials such as biosolids in engineering applications is of social and economic benefit to industrialized nations. Due to the shortages of natural mineral resources and increasing waste disposal costs, recycling solids wastes has become significant in recent years. This thesis presents research on the geotechnical properties of biosolids and investigates their sustainable usage as an embankment fill material, Field sampling of biosolids was conducted at three stockpiles at Biosolids Stockpile Area, Western Treatment Plant in Melbourne. An extensive suite of geotechnical laboratory tests were undertaken on untreated biosolids and biosolids stabilised with various additives. The geotechnical laboratory tests undertaken included index tests as well as more detailed tests. These tests included consolidation, triaxial, particle density, particle size analysis, Atterberg limits, compaction, California bearing ratio (CBR), hydraulic conductivity tests on untreated and well stabilised with admixtures such as lime, cement, bauxsol and fly-ash were determined and analysed in this research study. The Plaxis finite element analysis software was used to analyse the behaviour of various heights of embankments using stabilised biosolids with lime, cement, bauxsol and flyash. The primary, secondary and also the creep settlement were determined from the finite element analysis and analysed. In addition to the primary and secondary settlement, biodegradation settlement of the biosolids were also analysed by adapting theories that are presently used for landfills. As biodegradation is sensitive to pH values of the biosolids, a sensitivity analysis was undertaken by varying the pH value of the untreated biosolids and also the stabilised biosolids with admixtures. The laboratory testing results indicate that the biosolids stabilised with the required proportions of additives possess sufficient shear strength and bearing capacity to make them suitable for use as fill material. The results of the finite element analysis agree well with the laboratory results and indicate that biosolids, when stabilised with additives to the required percentages, can be used as stabilised fill in embankments