Evaluation of Embankment Dam Failure and Remedial Measure (Case Study of Gomit Dam in Amhara Region)
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Date
2016-10
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Addis Ababa University
Abstract
The main objective of this research is to evaluate the causes of Gomit embankment dam failure, emphasis on seepage and slope failure using Geo studio softwares and finally to come up with the possible remedial measure. Analysis of seepage was done using seepage analysis methods by analytical using Phreatic line and numerical using Geo studio software of Seep/W) method at normal and current pool level, compared with the current measured seepage at downstream i.e.0.004m3/s. The result shows that there was excessive seepage passing through the dam body and foundation. Analysis of static slope stability is performed to assess the safe design of upstream and downstream slopes of the dam. Slope/W software is used to calculate the factor of safety under the standard loading conditions for limit equilibrium methods of Ordinary, Bishop, Janbu and Morgenstern–Price method and compared with the observed downstream slope failure at steady state seepage. The result shows the dam was safe under this loading condition. However, from field observation, the downstream slope was failed. The major cause for downstream slope failure is the steady state loading condition in which the shear strength parameters of cohesion and angel of internal friction(C and Φ) value at current condition don’t attain the real value stated at the design document. The current C and Φvalue, the critical slip surface and the minimum factor of safety obtained from the back calculation using slope failure model just at failure. The calculated factor of safety just at failure is 0.996, which is less than the stability safety factor (FOS=1) and resulting slope failure at downstream that was similar to observed failure. Finally, since the dam was endangered to public life and property, the possible remedial measures proposed for seepage control are grouting, impervious blanket, rehabilitating the existing filter and toe-drains, adding both toe drains and drainage zones, and for downstream slope failure by removing the weak zone and failure part and fill with similar material, raise and re-constructing berms, regular maintenance and cover the downstream slope with grass.
Key words - Seep/W, Slope/W, Limit equilibrium method, Factor of safety
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Keywords
Seep/W, Slope/W, Limit equilibrium method, Factor of safety