Impact of Drawdown Speed on Slope Stability of Tendaho Dam Under Static and Pseudo Static Earthquake Loading Condition
No Thumbnail Available
Date
2018-09
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Dams are hydraulic structures used to store, control, divert water impounding it behind the upstream
side of dam in a reservoir for different purposes, like hydropower generation, water supply,
irrigation, navigation and transportation, etc. Although dams have many advantages, the risk that
may happen due to the failure still exists.
One of the most dangerous conditions causing failure of earthen dams’ upstream slope is speed of
drawdown condition when the countervailing upstream water pressure has disappeared with fastest
speed; it causes a danger to the upstream slope.
In this work Tendaho earthen dam, low permeability construction material, which is located on the
highly seismically active zone, Eastern Ethiopia Rift Valley was studied. The overall objective of the
study was assessing the impact of drawdown speed on Slope Stability of Tendaho dam under static
and pseudo static earthquake loading Condition by using different methods. Traditional limit
equilibrium methods and a finite element software, GeoStudio 2007 and 2012 computer program
were utilized in the slope stability analysis. Seep/w, Slope/w and Sigma/w GeoStudio sub program
were used to analysis and develop pore pressure curve and factor of safety curve for purpose of
reservoir water level operation monitoring.
The developed factor of safety curve shows that safety of upstream slope of the dam decrease during
drawdown condition and seismic load effect. The upstream slope of Tendaho dam is stable during
different drawdown speed and reservoir water level fall from FRL to MDDL. But, the worst case
scenario occurs when reservoir water falls below 387m from FRL (408m) within recommended
values of evacuation periods. In addition, during earthquake force was applied to the model the
critical drawdown level and evacuation period is 394m and 40 days, respectively. It is also found that
drawdown situation of Tendaho dam under reservoir operation have not affect on upstream slope of
the dam and emergency drawdown is not required till now. However, assessing the dam slope
stability under different drawdown speed and earthquake loading condition is important to avoid the
upstream slope sliding during drawdown condition in the future.
Description
Keywords
Earthen Dam, Finite Element Method, Limit Equilibrium Method, Factor of Safety, Earthquake Force, Slope Stability, Drawdown Speed