Engineering Geological Evaluation of Embankment Dam Foundation and Construction Materials Characterization of Fato Dam Site, Central Ethiopia
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Date
2023-08
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Addis Ababa University
Abstract
Our country, Ethiopia, has constructed a number of dam projects, including the Renaissance Dam in Abay. The location of the present study (the Fato Dam site) was located in upper Guder, which was a sub-basin of the Abay basin. Geographically located between 360252E/979403N at the right abutment and 360386E/979644N at the left abutment. However, the location of construction materials was here and there within a less than 1km radius around the dam site, except for the sand proposed from the Senkelle area. The local geology of the site was composed of basaltic volcanic formations (vesicular, porphyritic, and aphanitic) from top to bottom. The tops of the abutments were composed of residual soils. Especially in the right abutment, the thickness of the
soil reached around 30m from the surface.
The objective of the present study was the evaluation of the dam foundation and the characterization of the construction materials used for each zone of embankment. Evaluation of the foundation was mainly in terms of its seepage condition by plaxis software, with construction materials suitability in terms of location, quality, and quantity based on standards and finally recommend remedial measures for the seepage problems.
In order to meet the objective of the present study, literature reviews of different papers from both published and unpublished sources and reports of geotechnical investigations (previous work) of the site were used. In addition to these geophysical survey report, bore logging data and other in-situ data done by WWDSE in 2016 and Plaxis 2D software seepage analysis were performed to evaluate the seepage condition of the dam foundation and construction materials at the site.
From the borehole data and laboratory test results, the foundation soil was residual, dominantly cohesive soil. The soil of the foundation exhibits low to high plasticity in silty clay and also contains sand. The SPT results of the foundation were interpreted as medium to stiff consistence, while strength fell between 50 and 400 Kpa in the range of 4 to 15 N60 values for dominant in different depths. The permeability of the foundation soil was low to very low. The rock mass
rating of the foundation fell from fair to good in its quality. The strength test results of the foundation rock ranged from 42-478 Mpa uniaxial compressive strength, and the permeability packer test result was above the required lugeon (<3LU) values. These were due to the deep, localized fractures and weathering conditions of the site.
From the gradation analysis of construction materials, the core material was suitable as it meets the standards. The sand material proposed for the filter and transition zone from the Senkelle area was not suitable because it contained a fine percent above the standards. In turn, locally available basalt is processed and used for filters and transition zones. Rock fills, riprap, and rock toe were also prepared from a basaltic quarry located near the site.
The foundation of the embankment dam had seepage problems, so improvement techniques, three rows of curtain grouting of depth 0.75 H (height dam above reservoir), and around the highly affected toe of the dam should be treated with dental treatment of Shasta’s formula
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Keywords
Permeability, Seepage, Plaxis 2d, Core, Filter