Cause of failure of micro embankment dam and remedial measeres; a case of gomit micro embankment dam, amhara region, Ethiopia

Abstract

Safety of earth dams depends on the proper design, construction, and monitoring of actual behavior during the construction and operation of the structure. Many embankment dams are constructed in Ethiopia, However; their capacity reduces frequently before their design life time due to a number of reasons like improper design, lack of thorough investigation, inadequate care in construction and poor maintenance. In order to protect public safety, life and property, all embankment dams in service, regardless of their age, should be evaluated for their safe performance under all operational conditions. Gomit micro embankment dam were constructed in 2002 GC to irrigate 90ha of irrigable land, But the dam has not providing a service as per design. The primary objective of this study was to identify the cause of failure of GMED and coming with the possible remedial measures. Through field investigation the dam has revealed that excess amount of water seeps from downstream toe of the dam and from right foot side of the spillway. In order to realize such problem the analysis of seepage has been done with Darcy’s law phereatic line and SEEP/W software model. The analysis was focused on checking the design quantity of seepage of the dam with different methods. The largest value of seepage estimated by this study at the normal pool level is 6.05*10-3 m 3 /s, which is done by SEEP/W software model in the case of zoned dam with consideration of horizontal drainage filter and foundation; it is the actual type of the dam. In the same case but at the current water level quantity of seepage estimated by the software is 9.25*10-3 m 3 /s which is larger than that of the quantity of seepage estimated at the normal pool level, this shows that the presence of failure of seepage on the study area. From the design document seepage has estimated in the case of homogenous dam with consideration of horizontal filter but the actual type of the dam is zoned therefore there was a problem in quantification of seepage. Based on the result of the study grouting, dawn stream berm, horizontal drainage filter, toe drain and upstream impervious blanket were recommended as the possible remedial measures to the existed seepage problems.