INVESTIGATING THE CAUSE OF FAILURES OF EMBANKMENT DAM (A CASE STUDY OF GRINDEHO EARTH FILL DAM, NORTHERN, ETHIOPIA)

Abstract

Grindeho earth fill dam located at Agulae near Wukro town, Tigray Region, North Ethiopia. Grindeho earth fill dam planned to harvest 4.2MCM of water from a catchment area of about 78.03 km2 to introduce a modern irrigation practice downstream side of the dam. The planned net irrigable area was about 400ha. However, the dam performs under capacity and does not give service yet as a result of high water loss. Therefore, the main objective of this study was to focus on the investigation of cause and type of failures of Grindeho earth fill dam. To achieve the objectives of this study, primary and secondary data has been collected from the study site, design documents, internet sources related research, references and books for emphasis the literature review, and interviewing the site engineer, hydro geologist and others. The analysis was conducted using GEO-SLOPE software to analyze the seepage flux, slope stability and stress deformation. The amount of Seepage losses through the abutments of the dam based on the design document and laboratory test data are 8.9 *10-4 m3 /sec and 1.1*10-2 m3 /sec, respectively, however the actual seepage losses of the dam based on measurement of the seepage flow at the downs stream side is 0.221 m3 /sec which is much greater than the expected as per the design, the dam has been exposed for piping failure. The stability analysis results based on design document data as well as laboratory test data indicated that the critical upstream and downstream slope of the dam are safe for the possible loading and operation cases. The stress-deformation analysis during the empty and full reservoir conditions and the maximum horizontal and vertical displacements are calculated. The maximum horizontal and vertical settlement for full reservoir conditions is found to be 0.20% and 0.94% of the dam height respectively which is within the safe limit as to deformation is considered. The impervious core material is not safe against the inside cracking and hydraulic fracturing due to the horizontal displacement, however, the dam couldn’t be affected by overtopping problem through the impact of current vertical settlements