Abstract:
Dams have one of the most important roles in utilizing water resources. An
embankment dams are more common than any other type of dams. Seepage and slope
stability failures cause completely failure of embankment dams. Dam failures not only
risk public safety, they also can cost our economy millions of dollars in damages. The
prime objective of this research was to assess Arjo-Dedessa embankment dam,
highlighting on seepage and slope stability analysis. The study area is found in
Oromia regional state between East Wollega and Bunno Bedele Zone. The dam is
located on Dedessa River, tributary of Blue Nile River. Analysis of seepage quantity
was done by Darcy’
s phreatic line, and SEEP/W software model for both
homogeneous and zoned dam. The expected quantity of seepage estimated with the
SEEP/W software model analysis that includes foundation seepage is 6.6*10-6
m
3
/sec
which was compared with the quantity of seepage estimated at the designed document
that is 4.16*10-5
m
3
/sec. Therefore, the design document has no problem of
quantifying the expected quantity of seepage. But seepage is visible at the
downstream berms of dam and downstream face of the existing Upstream Coffer
Dam. The document stated that, the shell material used for the design was larger than
the required size of shell material which may create Wet spots or seepage problem in
the embankment. Even though, the dam has a problem data on construction history.
Slope stability analysis is to contribute to the safe and economic design of upstream
and downstream slope of the dam. Factor of safety was calculated under the standard
loading conditions for limit equilibrium methods using entry and exit trial slip
surface. The factory of safety obtained by Morgenstern-Price method for end
construction is (FOS=1.99), for steady state (FOS=2.03) and rapid drawdown
(FOS=2.91).The result shows that dam was safe when compared with international
standards and design document. However, at the design document shell material
hadn’t been designed properly. From field observation, there was also the oversized
stone of shell materials and wrong placement of stones in the downstream of the dam
which may leads to Face (slope) failure on the downstream slope of the dam. Finally
the paper concluded that the possible remedial measures for seepage controls are
impervious blanket, grouting, and for downstream slope failure by removing the weak
zone and fill with similar graded material, regular maintenance and cover the
downstream slope with grass.
