Dam Heightening (Case Study Gefersa-I/II Dam)
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Date
2019-05-15
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Addis Ababa University
Abstract
Sediment problem is a major problem which highly reduces the live storage capacity of the reservoir. Gefersa-I/II dam is one of the major embankment dams in our country Ethiopia which trap huge amount of sediments in each year. Due to this reason AAWSA decide to heighten the existing dam up to 5m effective height with 2m additional freeboard. This case study mainly focuses on determining the suitable and stable heightening type which is compatible with the existing dam condition. From different point of view this study preferred to heighten the existing embankment as homogenous clay fill embankment. Due to the upstream condition of the existing dam, most of the fill is done at the downstream side of the embankment. this create good environment to start the fill on the crest of existing dam by letting 2m width for working space. While 2m working space is provided at the upstream side of the dam automatically berm is created with 2m width. Since soil material is sensitive for deformation, 7m berm is provided at the downstream side of the dam to prevent such problem. The geometry of the heightening part was fixed as 1V: 3H at the upstream face and 1V:1.45H and 1:4.17 at the downstream side (from top to bottom) after a number of trials. Analysis was conducted using Geostudio 2007 software as a major tool. Steady state seepage analysis was conducted and the seep water to the body of the dam is around 1.952*10-7m3/sec/m. During this study the stability of the dam was analyzed and as the result indicates, the dam side slope is safe for all loading condition. Deformation and earth quake analysis also conducted and, as the result shows the vertical and horizontal settlement was found in allowable range.
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Keywords
Gefersa-I/II Dam, Heightening, Dam Heightening