Biomediated improvement of tropical residual soil for compacted liner in sanitary landfill
Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Teknologi Malaysia
Abstract
Clays soils of very low permeability (k = 1x10-9 m/s) are often used for construction of compacted clay liner in sanitary landfill systems. However, such suitable clay soils are not always readily and widely available. In practice, native soils are commonly improved using either conventional or alternative materials to meet the standard criteria for suitable materials for compacted clay liner. Despite their effectiveness, most conventional and alternative soil improvement materials are not sustainable, they are environmentally dangerous, and costly. Recently, biomediated and bio-inspired soil improvement techniques have gained tremendous attention due to their sustainability, environmental friendliness, and cost-effectiveness. Enzymatic induced calcium carbonate precipitation (EICP) is one of such technique that utilizes free urease enzyme to produce calcium carbonate precipitation via urea hydrolysis process. This study employed the use of EICP to improve the engineering properties of residual soil for compacted clay liner. The study investigated the effect of variation in the concentration of cementation solution (0.25 M – 1.25 M) and curing periods (3, 7, and 14 days) on the amount of calcium carbonate precipitation via a test tube test. The research determined the effect of EICP treatment at various concentration of cementation solutions (CCS) (0.25 - 1.00 M) as well as moulding water content and compaction energy (CE) - British standard light (BSL) and reduced British Standard light (RBSL) on the physical properties; compaction behavior; hydraulic conductivity; volumetric shrinkage strain (VSS); and unconfined compressive strength (UCS) of the residual soil. Chemical and microstructural analyses were performed on the natural and EICP treated soils to understand the mechanism involved in change in soil properties due to EICP treatment. Digital image technique (DIT) was also adopted to evaluate the influence of biocementation on the leachate penetration pattern and hydraulic conductivity of EICP treated residual soil. Preliminary results from the test tube test indicated that the highest CaCO3 precipitations of 1.577 g is achieved at 1.00 M CCS. The results also demonstrated that curing periods has insignificant influence on the amount of calcium carbonate precipitations. The results showed that EICP treatment significantly improved the plasticity behaviour, hydraulic conductivity, UCS, and VSS of the residual soil. It was found that at 30 oC, a minimum k value of 6.2 x 10-10, a maximum UCS of 710 kPa, and the lowest VSS value of 1.49% were determined at 1.00 M when the soils were compacted using BSL effort. It was found that the soils treated with higher CCS values of 0.75 M and 1.00 M satisfied all the requirements of k = 1x10-9 m/s, UCS = 200 kPa, and VSS < 4% when compacted using BSL. Also, all the criteria were met using RBSL compactive effort when the soil was treated with 1.00 M. It was revealed through ANOVA test that variation of CCS, curing temperature and CE have significant influences on the k, UCS, and VSS values of the EICP treated soils. The curing period and moulding water were found to have an insignificant effect on the parameters. It was also revealed that the rate of leachate penetration had been reduced significantly upon EICP treatment. The results obtained from chemical and microstructural analyses have confirmed the formation of calcium carbonate precipitations in the residual, and calcite was the main minerals produced due to EICP treatment. In conclusion, it was found that biocementation via EICP in residual soil had significantly improved the engineering properties required in compacted clay liner design, and 1.00 M was the optimum concentration of cementation solution.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Sanitary landfills, Soil bioventing, In situ bioremediation, Clay soils—Testing