Long-term settlement prediction for wastewater biosolids in road embankments

Abstract

An innovative research study was undertaken to characterize the settlement characteristics of aged wastewater biosolids to facilitate its long-term settlement prediction when used as fill material in road embankment applications. Settlement can be sub-divided into compression due to consolidation and deformation attributed to biodegradation. Results of an extensive geotechnical laboratory evaluation including compaction characteristics, shear strength parameters, coefficient of consolidation, compression index, swell index and coefficient of secondary consolidation were used to predict the consolidation settlement of biosolids in road embankments. Other relevant parameters for biodegradation settlement prediction, such as organic content, pH and electrical conductivity of the biosolids were also determined. The biodegradation induced settlement of a road embankment built with aged biosolids was subsequently analyzed by applying an analytical method used previously for municipal solid waste landfills. The adopted model shows that the rate of biodegradation settlement reduces with the reduction in pH values of biosolids. The model also suggests that the time taken for full process of biodegradation decreases dramatically with pH value of the biosolids between 0 and 6 and then increases exponentially with pH value of the biosolids between 8 and 14. A framework has been developed to predict the total settlement of wastewater biosolids in road embankments for end-users.