Geotechnical investigations on earth dams in Sri Lanka unnichchai dam as a case study

Abstract

Sri Lanka is a country where there are large numbers of earth dams. Most of them are suffering partial failures due to excessive seepage, piping, excessive lateral deformations etc. But limited investigations have conducted on the performance of earth dams from the geotechnical point of view. This paper draws attention to some of the possible failure mechanisms based on steady state seepage, rapid draw down, and response due to an earthquake by analysing a set of computer based models of Unnichchai earth dam. The main objective is to evaluate the risk of failure for above mentioned mechanisms. The analysis revealed that the factor of safety against rapid draw down condition and in steady state conditionis lying closely for selected conditions and fairly high enough to obtain good performance. Behaviour of the dam under seismic loads urn analysed using computer models and manual methods and showed acceptable factor of safety against liquefaction. When overall result is considered it can be stated that the Unnichchai earth dam is performing well under normal conditions prevails in Sri Lanka.