Stability Assessments on the Selected Reservoir Slopes of Ajima Earth Dam North Shoa, Central Ethiopia
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Date
2024-01
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Addis Ababa University
Abstract
This study was conducted in the Ajima Chacha earthen dam area in North Shoa, central Ethiopia. The study aimed to assess the stability of three critical slopes selected in the dam reservoir. These slopes were selected based on their geometry, steepness of slopes, slope material weathering conditions, rockmass discontinuity, and lithology type, which makes them prone to failure. The failure of these slopes can lead to significant problems in the dam reservoir, which is why assessing their stability is crucial for ensuring the safety of the dam.
To conduct the stability analysis, a comprehensive field investigation was undertaken, and rock and soil samples were collected from the selected slopes for testing in the laboratory. The input parameters obtained from these tests were used in the slope analysis carried out using Fast Lagrangian Analysis of Continuum (FLAC2D) and DIP software. However, FLAC2D was mainly used for stability analysis in this research.
The Kinematics analysis was conducted on the upper section of RS-1, which is located on a highly fractured and weathered rhyolite unit and toppling failure type is shown from the DIP analysis. The slope analysis of the entire section of RS-1, RS-2, and RS-3 was done using FLAC2D. The FOS (Factor of Safety) for RS-1, RS-2, and RS-3 was 1.63, 1.42, and 1.32, respectively, under static dry conditions. Under static saturated conditions, the FOS for RS-1, RS-2, and RS-3 was 0.99, 1.12, and 1.24, respectively. Since the FOS (Factor of Safety) for slope one (RS-1) under static saturated conditions was less than one which indicating instability and measures should be taken to stabilize the existing slope. Furthermore, evaluating the dam reservoir slopes' stability under seismic conditions would provide a better understanding of dam safety in the long term.
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Ajima Chacha, Slope Stability, Kinematic Analysis, Finite Difference Method, FLAC 2D, Insitu Tests, Factor of Safety