Browsing by Author "Nawarathna, THK"

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item: Conference Full-text
Effect of organic bio-polymer on bio-mineralization of CaCO3
Nawarathna, THK; Nakashima, K; Kawasaki, S; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y
Organic matrix in the biogenic CaCO3 has a significant influence on the CaCO3 crystal growth, its polymorphs and morphology. In this research, effect of the cationic and anionic organic bio-polymers on the crystallization of CaCO3 was investigated in microbial induced carbonate precipitation (MICP) process. In the current study, poly-L-lysine and poly-glutamate were used as cationic and anionic biopolymers, respectively. Urea hydrolysis by ureolytic bacteria Pararhodobacter sp. led to CaCO3 formation in the presence of Ca2+ ions. The reaction was conducted with the addition of the polymers under different conditions. After oven-drying precipitation, the amount of precipitate was measured and morphology of the precipitate was analyzed by using scanning electron microscope. Bell-shaped curve was obtained in the relationship between the amount of the precipitate and the poly-L-lysine concentration. However, amount of precipitate remained approximately constant with the increase of the poly-glutamate concentration. In the presence of poly-L-lysine, morphology of the crystals changed from well-developed rhombohedral crystals to ellipsoidal shaped aggregates. But in poly-glutamate addition, polyhedral and spherical crystals are predominant.
item: Conference-Full-text
Effects of discontinuous properties on the stability of tunnels
(Department of Earth Resources Engineering, 2010-09) Nawarathna, THK; Kulathilake, LKNS; Perera, HDH; Premalal, PAM; Dharmaratne, PGR; Chaminda, SP; Rohitha, LPS; Ratnayake, NP; Abeysinghe, AMKB; Premasiri, HMR; Karunaratne, S
Many failures of underground openings during excavation are closely related to discontinuous properties of the surrounding rock mass and they affect differently to the stability of underground openings. In this research, attempts have been made to study the effect of discontinuities over the rock mass stability with various infilling materials, dip angles and strikes by using laboratory scaled models. Specimens were casted using cement concrete mixture and five different dip angles (30°, 45°, 60°, 75°, 90°) and three infilling materials (quarry dust, kaolin and graphite) have been selected for the study. Models were tested to determine their uni-axial compressive strength. The results indicate that the dip angle of the joints and the orientations of the tunnel axis have significant impacts on the stability of the tunnel. The dip angle at 90°, perpendicular to the tunnel axis shows a higher stability while the angle at 45°, shows the lowest stability. The tunnels excavated with axis parallel to the discontinuous plane should be avoided as much as possible. If it is unavoidable in any circumstances, well designed support system should be used. Types of infilling materials also affect the stability of the tunnel with graphite being the most unfavourable among the selected materials.
item: Thesis-Full-text
Estimation of the stability of embankment slopes using field monitoring data
Nawarathna, THK; De Silva, LIN
In Sri Lanka lands underlain by soft, weak and problematic soil are being use for various constructions due to rapid development and the lack of suitable lands. Construction of an embankment over soft soil is challenging due to its low shear strength and high compressibility nature. As a result of that embankment can be subjected to a shear failure or excessive settlement. Assessment of the stability of the embankment is vital to ensure a safe embankment and stability can be evaluated by using available analytical methods or field monitoring data. Use of field monitoring data to evaluate the stability is easy and more practicable. In Sri Lanka Matsuo chart which is based on the field monitoring data was used for the prediction of stability of the embankments in the Colombo Katuanayaka highway project. However applicability of Matsuo chart for various embankment conditions is still questionable. This study was carried out to investigate the applicability of Matsuo chart for various embankment conditions using advanced numerical tools. Two test embankments published in the literature and three embankments, which belong to the Colombo - Katunayaka expressway were analyzed by using Finite Element Method, Limit Equilibrium Method and Matsuo chart and compared with the field data. Further, the effect of embankment width, height and the subsoil parameters on the prediction of stability using Matsuo method was investigated. Research finding verify that the Finite Element Method, Limit Equilibrium Method and Matsuo chart can predict the stability of the embankment accurately and Finite Element Method can be used to predict the deformation characteristics. Stability of the embankment is directly proportional to the un-drained shear strength of the sub soil and Factor of Safety values decrease with the increase of the embankment height. However it was found that the embankment width has little influence on the factor of safety.
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.