Thesis Defence: Influence of Biochar and Polymer Amendments on Strength, Shrinkage and Water Retention Properties of Clay-Based Landfill Liners

Usmita Adhikari, supervised by Dr. Sumi Siddiqua, will defend their thesis titled “Influence of Biochar and Polymer Amendments on Strength, Shrinkage and Water Retention Properties of Clay-Based Landfill Liners ” in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering.

An abstract for Usmita Adhikari’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Please email sumi.siddiqua@ubc.ca to receive the Zoom link for this defence.

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Abstract

Fluid movement in the unsaturated zone is crucial in various geoenvironmental engineering challenges. These include designing landfill cover and liner systems for municipal waste disposal facilities. To understand seepage, unsaturated soil resilience, and other hydromechanical parameters in unsaturated soil, the establishment of the soil water characteristic curve (SWCC) and soil shrinkage characteristics curve (SSCC) is necessary. This study provides comprehensive experimental research that was utilized to develop SWCC and SSCC of landfill liner soil. Two sustainable additives, Bis (2-Hydroxyethyl) terephthalate (BHET), a chemically depolymerized form of Polyethene Terephthalate (PET) and Biochar, are used in the liner soil. The adoption of biochar in soil improvement has become a feasible and eco-friendly alternative for establishing hydraulic barriers in waste disposal facilities. Additionally, BHET polymer possesses desirable properties such as cementitious behavior, non-toxic nature, low biodegradation and ability to adsorb heavy metals, which makes BHET a promising candidate for inclusion in landfill liner material. However, unsaturated behaviour, including shrinkage and water retention of BHET-treated biochar-amended soil, remains unexplored. Therefore, different dosage of biochar (0%, 5%, 15% and 25%) and BHET polymer (0%, 2% and 3%) was mixed with locally available soil-clay mixture and thus, several tests such as, compaction, compressive strength, volumetric shrinkage, water retention, electrical conductivity were performed. Furthermore, microscopic examinations were carried out using Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy.

Results showed that compressive strength, water retention capacity, shrinkage limit and electrical conductivity of the composite soil increased with biochar and polymer treatment. The Air Entry Value (AEV) increased with biochar and BHET polymer treatment; 0% to 3% incorporation of BHET polymer increased the AEV of soil up to 23.35 %, as evidenced by the upward shift of the SWCC curve. Conversely, SSCC exhibited a downward shift when BHET polymer was introduced in biochar-treated soil. The outcomes showed that the addition of these eco-friendly materials can greatly help with moisture retention and reduce the shrinkage of liner soil. The results are promising and provide a framework for the use of waste products like biochar and PET in significant geotechnical projects like the construction of solid waste disposal facilities.