Geotechnical characteristics of stabilised aged biosolids

Stockpiles of air-dried sludge from wastewater treatment plants, known as biosolids, are constantly increasing worldwide. This subsequently adds to the urgency of stabilising biosolids in an effort to convert them into a suitable construction material for use in engineered fills. This paper reports the result of a laboratory testing programme on biosolids stabilised with two types of waste materials, namely, bauxsol and fly ash. The biosolids collected from the Western Treatment Plant in Melbourne were stabilised in different ratios and tested to determine their compaction, strength, permeability and deformation characteristics. Both static and dynamic compaction methods were used in the preparation of the test specimens. Results suggest that the hydraulic conductivity values of biosolids consistently decrease with increasing amounts of additives, which is an indication of decreasing void ratio of material. In addition, increasing the amount of additives was found to lead to a subsequent decline in the compressibility of the stabilised biosolids. The strength of the biosolids samples increased with the addition of bauxsol and fly ash, with the highest shear strength found to be achieved with around 10% fly ash mixture. The application of stabilised biosolids in road embankments is discussed as a sustainable solution in geotechnical engineering applications.