Analysis of liquefaction potential of foundation soils of the right embankment dam at Isimba Hydro Power Plant

Abstract

Earthquake occurrences have led to the failure of very many embankment dams worldwide. This failure is accompanied by catastrophic and severe economic and life losses. Majorly the effects of earthquakes are manifested through failure of foundation material and cracking of the embankment dams which leads to erosion of the earth materials used for the dam construction and then to total failure of the whole dam structure. The foundation material therefore is checked for susceptibility to liquefaction due to earthquakes and also the evaluation of the triggering of liquefaction. The susceptibility to liquefaction of foundation material is tested using soil index properties while the evaluation of triggering of liquefaction takes into the consideration the loading imposed on the soil during an earthquake and then the soils’ ability to sustain the cyclic stresses. The project focused on the foundation material of the right embankment dam of Isimba hydro power plant. The following methods were used to achieve the project objectives. A criteria proposed by Bray and Sancio 2006 was used to analyze for the susceptibility of the foundation material to liquefaction. Field work was done which involved the collection of soil samples from the section of the right embankment dam that is at KOOVA island and beyond the river channel following the dam axis. The depth to ground water table was measured in pit 2. Laboratory testing was carried out on the 3 samples. The tests included; particle size analysis, Atterberg limits, natural moisture content and all was done according to British standards. The results obtained were then analysed and the soils were classified as sands and it was found out that the foundation material of RED of Isimba HPP is not susceptible to liquefaction. SPT data analysis was done. This involved initially obtaining recent geological investigation reports having results of the standard penetration test which was carried out at KOOVA island. With the results, a detailed analysis of the data was done using a semi empirical procedure proposed by Idriss and Boulanger 2008. The factor of safety against liquefaction was calculated and the values indicate that the foundation material is safe from liquefaction. (FOS>1)