Browsing by Author "Thilakarathne, T.M.D."

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Open Access
Computational Approach for Determining the Variation of Coefficient of Secondary Compression in Secondary Settlement Prediction of Soft Soils
(Sri Lanka Institute of Information Technology, 2023-03-25) Thilakarathne, T.M.D.; Vidurapriya, K.V.D.; Thilakasiri, H.S.
Secondary consolidation settlement takes place in soils after the completion of primary consolidation settlement, which is due to the dissipation of pore water pressure under the applied loads. The secondary settlement usually occurs due to the plastic adjustment of the soil particles and most commonly takes place in organic fine grained soils or soft soils. Hence, it is important to accurately estimate the secondary settlement in soft soils as the final stability of infrastructures built on soft soil grounds mainly depends on the amount of secondary settlement that takes place after the end of primary consolidation settlement. The coefficient of secondary compression (C) is a governing parameter in predicting the secondary settlement which is the slope of the consolidation curve for void ratio versus time. Also, various empirical correlations have been found by the past researches to find the value of the coefficient of secondary compression. In most of the instances, the secondary settlement is estimated by considering the coefficient of secondary compression as a constant value. However, the C value shows a variation with time and this could affect the secondary settlement estimation. Hence, it is necessary to investigate how the variation of coefficient of secondary compression affects the estimation of the secondary settlement in soft soils. In this study, the settlement data obtained from the Weligama Bay Marriot Resort and Spa project, Sri Lanka, is compared with the settlement values obtained from a computer generated programme. The progarmme simulates the settlement by considering the variation of the coefficient of secondary compression and by considering a constant coefficient of secondary compression value. The results show that the consideration of varying coefficient of secondary compression (with time) gives more accurate results than considering a constant coefficient of secondary compression in settlement prediction in soft soils.
Open Access
Strength Gain of Organic Soil Deposits Subjected to Increase in the Effective Stress
(Sri Lanka Institute of Information Technology, 2023-03-25) Nanayakkara, D.A.S.; Thilakarathne, T.M.D.; Thilakasiri, H.S.
Organic soil has weak shear strength properties in its natural texture. However, a significant gain in strength can be achieved in such soils by increasing the effective stresses using preloading techniques. This research focuses on the organic soil deposits in Sri Lanka by analyzing the data from Colombo- Katunayake Expressway (CKE) project and Elevated Highway (EH) project spanning from New Kelani Bridge to Athurugiriya. As a developing country, Sri Lanka is facing a huge challenge due to its limited land available towards the infrastructure development. Therefore, construction should also be directed on organic soils despite of considering its weak shear strength properties as the soil can be modified to enhance its properties. To predict the strength gain of organic soils subjected to effective stresses, empirical correlations are used such as Skempton and Bjerrum equation (1957). As depicted in such correlations, the ratio of undrained shear strength and effective overburden pressure is observed against the Plasticity Index (PI) using field data. From the results of the analysis, it is discovered that using empirical correlations is very conservative for organic soils within the Sri Lankan context. Particularly, use of empirical correlations is very safe but beyond the economic considerations. In the extension of the research, an argument is generated to validate the use of PI to predict normalized shear ratio. To validate the argument, SPSS statistical software was used to perform the multiple regression analysis having PI, natural void ratio and organic content as the independent variables. From the statistical analysis, it was found that using only PI to predict the strength gain is not conservative for Sri Lankan organic soils subjected to effective stresses. These generated results are identical to conclusions drawn governing the inorganic soils in the state of Missouri (2011).