Investigation on the causes of failure of Tana Beles Weir
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Date
2019-07
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Addis Ababa University
Abstract
An investigation on Tana Beles diversion head-work is carried out for this research work and
attempt is made to understand the failure problems encountered. This serve for different
purposes such as for construction of new diversion structure (either as replacement for existing
structures, or as an entirely new structure), rehabilitation of existing structures (from minor
repairs to complete re-engineering either to maintain existing function, or to meet new
requirements).
Hydrology and hydraulic analysis, structural analysis and evaluation of the foundation
condition of the weir has been made to investigate the causes for the failure of the weir.
The hydrology analyses is made by Hec-hms and the result shows that the peak flood used for
the design of the weir is smaller than the result obtained in this investigation, but the water way
of the weir built can accommodate the estimated peak flood. Models used for the hydrology
analysis include Global Mapper, Arc-GIS, Hec-Geohms and Hec-hms. On the other side,
hydraulic design is evaluated and the evaluation exposes the absence of concrete floor, absence
of energy dissipater and protection works on the hydraulic design of the weir and clogging of
under sluice as a cause for the failure of the weir. The structural analysis involves checking
stability analysis of the weir against overturning, sliding and shear. Surveying data upstream
and downstream of the weir is collected and foundation condition were investigated by
comparing the collected surveying data with the design bed level.in addition to this the applied
foundation treatment is evaluated by comparing it with standards and found that the main
structure was built on weak foundation which activates the weir failure. This investigation
shows that the main cause of Tana Beles weir failure is due to the weak foundation condition
of the weir and absence of the necessary concrete floor and energy dissipater on its design.
Finally, the remedial design for the weir is recommended.
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Keywords
Analysis, Concrete Floor, Diversion, Downstream, Energy Dissipater, Gates, Head work, Regulator, Scour, Seepage, Silt, Stability,