Characterization and Suitability Analysis of Embankment Material for Dam on Berga River, Central Ethiopia
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Date
2013-05-05
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Addis Ababa University
Abstract
Material quality and suitability is one of the main criteria for the success of embankment dams. Seepage through the embankment, foundation, and abutments must be controlled and collected to prevent excessive uplift pressures, piping, sloughing, dissolution and erosion of material. The embankment, foundation, and abutments must also be stable against slumping, sliding and sloughing during construction, reservoir operation and during events such as earthquake and floods. The present study was conducted on a proposed Berga earth dam which is located on river Berga in central Ethiopia, located approximately 11.5 km north of Holeta town. The main objective of the present study was to characterize and to assess the suitability of the proposed construction material for various zones of the embankment dam. Besides, it was also proposed to evaluate and characterize the dam foundation for its suitability for the dam.
For foundation characterization data pertaining to Rock mass classification (RMR) was collected from the left abutment. Further, stability analysis was made for both the abutments. The left abutment was found to be stable whereas, right abutment was analyzed for rotational mode of failure. The results revealed that right abutment will be stable only for static dry condition and for anticipated worst conditions the abutment slope would be unstable. Further, the soil samples were collected from the dam site and were analyzed. From the investigations conducted during present study it was found that the dam site possesses weakness in terms of seepage potential and abutment slope stability condition. However, in terms of bearing capacity, both the abutments have high capacity as they are composed of very strong basalt rock.
In order to assess the general suitability of the construction material for various zones of the embankment from the proposed borrow areas samples were collected and tested for grain size distribution, Atterburg limits, swelling potential, activity and permeability. Besides, data on soil properties from previous study was also reviewed and analyzed. Besides, mineralogical analysis was also made for core samples. In order to assess the general suitability of the filter material various filter criteria were applied. In general the proposed construction material for the dam is slightly plastic in nature. Thus, it is anticipated that this may result in to high compressibility which may lead to instability. Also, the proposed filter materials contain more fine materials than the desired percentage.
Also, the initial design was prepared by using Taylor’s stability numbers. Later, the stability of the embankment slopes was analyzed by using SLOPE/W and SARC software. The stability analysis results revealed that the dam design will be stable when there is no water in the reservoir. However, the factor of safety will decrease under anticipated adverse conditions which may possibly result in to the failure of the slopes.
Finally, in general it is found that proposed dam site is feasible with minimum engineering geological problems and construction material is available within the economic distance though it requires certain treatment for its improvement. Based on the findings of the present study certain remedial measures are forwarded.
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Keywords
Characterization, Suitability Analysis, Embankment Material, Dam on Berga River, Central Ethiopia