Browsing by Author "Priyantha, SM"

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    item: Article-Abstract
    Investigation of the accuracy of the elastic settlement estimation methods and the extrapolation techniques of plate load test results
    Thilakasiri, HS; Priyantha, SM
    Accurate estimation of the settlement of shallow foundations is an important aspect in the design of such foundations. Most often elastic settlement estimation methods are used in the estimation of settlement of shallow foundations. In addition, plate load tests are also performed to estimate the settlement of shallow foundations. Since a smaller size plate is used in the plate load test, the settlement obtained from such tests should be xtrapolated to the actual size footings. Even though there are large number of settlement estimation methods and extrapolation techniques for plate load test results, the verification studies of the accuracy of the methods are very rare. It is very often observed that the settlement of shallow foundations are estimated based on the plate load tests carried out in layered soil medium, where a stiff fill soil layer overlying a soft soil. Extrapolation techniques of the plate load test results are highly questionable under such situations. A finite element model was developed using the software called PLAXIS to simulate the settlement of footings. The developed model was used to model some case studies presented in the literature to investigate the accuracy of the model predictions. Thereafter, parametric studies were carried out to investigate the accuracy of: (i) commonly used elastic settlement estimation methods; (ii) the commonly used extrapolation techniques in the homogeneous subsurface conditions; and (iii) the commonly used extrapolation techniques in the two layered medium with a hard layer overlying a soft layer.
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    item: Thesis-Full-text
    Seismic hazard assessment for Colombo city with local site effects
    Priyantha, SM; Lewangamage, CS
    floods, droughts, landslides etc. Due to the experiencing of ground shaking in last few decades and the disaster on 26th December, 2004 due to tsunami, Sri Lanka cannot further treated as an earthquake damage free country. Few research has been carried out to investigate seismic hazards at Colombo city area and the response spectrum at rock level for Colombo city area has been proposed with the PGA (Peak Ground Acceleration) of 0.1g. However, no studies have been carried out to develop earthquake response spectrum for Colombo city with local soil variations. This study discusses generalized soil profiles for Colombo city and earthquake response spectrum with local site effects for Colombo city area. 77 borehole logs done at the study area are collected and locations were plotted on a map of study area. Eight vertical sections were obtained through the study area and using them eight soil profiles which have horizontal soil layers were developed. All eight profiles highlight that the average soil cover in Colombo city area is about 20m. Just above the basement rock dense to very dense silty sand/ sand layer is present. Topmost layer also having loose to dense sandy soil. In between both of sand layers, very loose to loose clay/ silt or organic material layer is encountered in all boreholes. The developed soil profiles were used to analyze with earthquake motions using the computer software called EduShake. The six earthquake motions are applied at rock level as input motions. The response spectra at rock level and the response spectra with the local soil effects were obtained as the output file. The program was run for the eight soil profiles and obtains the average value of both output files as final result. Finally, earthquake response spectrum has been proposed for Colombo city area and it was compared with existing response spectrum at rock level for Colombo city. According to this study, the PGA with local site effects is 0.13g for Colombo city area.