Browsing by Author "Thilakarathna, AMGGG"

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item: Conference-Abstract
Isolation and characterization of ureolytic bacteria from landslide-prone areas in Sri Lanka for the stabilization of unstable slope surface by bio-cementation
(Division of Sustainable Resources Engineering, Hokkaido University, Japan, 2024) Srirajatheepan, R; Ducksan, S; Srirangan, S; Thilakarathna, AMGGG; Nawarathna, THK; Gowthaman, S; De Silva, LIN; Karunawardena, A; Iresha, H; Elakneswaran, Y; Dassanayake, A; Jayawardena, C
Landslides are natural disaster, long-existing as one of the geotechnical threats in the central region of Sri Lanka. During the monsoon period of every year, number of human lives are lost due to the landslides. Therefore, early recognition of the potential areas and implementing landslide mitigative measure are essential to prevent the damages. Portland cement and chemical grouts are typically used to enable a protective cover over the slope surface. However, these approaches are recognized environmentally detrimental and expensive. The use of bio-grouting materials is a new proposal to stabilize the slope surface, disclosing the likelihood of eco-friendliness and sustainability. Among various bio-grouting techniques, microbial induced carbonate precipitation (MICP) has gained much attention recently. MICP is a process that triggers the precipitation of calcium carbonate using the metabolic aid of ureolytic bacteria. This paper presents the initial works carried out to isolate and characterize urease-producing bacteria that are competent for the application of MICP-based stabilization of Sri Lanka's unstable slopes. Few landslide-prone areas were identified in Matale district (of Sri Lanka) with the support of National Building and Research Organization. From each location, soil samples were obtained in sterile centrifuge tubes and transported to the laboratory. After a series dilution, soil samples were plated on trypticase soy broth agar medium and incubated at room temperature for two days. Grown-colonies were then carefully separated on new agar plates. Initial screening of potential bacteria was carried out using phenol red pH indicator. The growth and urease activity of identified bacteria were then measured over time. A set of test tube precipitation tests was also performed to verify the applicability of the bacteria. The results indicated that most of the identified bacteria exhibited adequate growth and urease activity during the second and third days of the culturing. The test tube test revealed that the natively-isolated bacteria were highly potential to produce CaCO3, thus disclosed the potential for MICP application. Based on the preliminary results, laboratory-scale slope model tests and field-trails are to be performed in the subsequent phase of this work.
item: Conference-Abstract
Polymer-modified microbial induced carbonate precipitation for stabilizing unstable slope surfaces in Sri Lanka
(Division of Sustainable Resources Engineering, Hokkaido University, Japan, 2024) Chandraleka, K; Sabeshraj, P; Thilakarathna, AMGGG; Nawarathna, THK,; Gowthaman, S; De Silva, LIN; Karunawardena, A; Iresha, H; Elakneswaran, Y; Dassanayake, A; Jayawardena, C
Cement grouting is a widely using technique in Sri Lanka to stabilize the unstable slope surfaces. Although cement grouting has been identified as an efficient mean of stabilization, it is not an ecofriendly practice. Polymer-modified microbial induced carbonate precipitation (PM-MICP) has been recently recognized as a promising pathway to produce bio-grout material that has the potential to be used for stabilizations in the place of cement. In MICP, calcium carbonate bio-cement is produced through enzymatic reactions. The efficiency of the process can be further improved by incorporating bio-polymer. In this research, the viability of the PM-MICP to stabilize the Sri Lankan unstable slope surfaces was evaluated. Representative soil samples were collected from unstable slope areas in Matale district of Sri Lanka. Sporosarcina pasteurii was the ureolytic bacteria, and chitosan was the natural biopolymer used for the experiments. Laboratory scaled specimens were prepared and treated using (i) saturation and (ii) percolation methods; for different concentrations of cementation solutions (i) 0.3 mol/L and (ii) 0.5 mol/L); (i) with 0.05% and (ii) without chitosan. Bacteria culture was injected twice during the fourteen days of treatment, while the cementation solution was injected daily. After the treatment, samples were removed from the mold and subjected to a comprehensive evaluation program. Laboratory-scale model slope was also prepared and treated after 28 days of treatment, and the surface strength was determined. The samples treated with 0.5 mol/L cementation solution and polymer, exhibited a strong solidification compared with the specimens treated without polymer in both saturation and percolation methods. However, bottom of samples showed a weak solidification due to the less penetration of the bacteria and cementation solution to the bottom of the sample. In without polymer case, a weak solidification was observed for the samples treated using percolation method compared with the saturation method. Higher cementation could be achieved for the samples with 0.5 mol/L cementation solution than the sample with 0.3 mol/L. Comparatively, the surface strength was higher for the slope treated with polymer, thus the PM-MICP can be recommended as a promising alternative approach to conventional cement grouting for stabilizing the unstable slope surfaces in Sri Lanka.