Structural Stability of Gravity Dams: Comparisons of Performance Indicators

Concrete gravity dams built in the twentieth century has started to experience structural issues due to aging. Furthermore, rising water levels in reservoirs caused by climate change make dams more vulnerable. It is therefore necessary to develop effective methods to assess structural stability to facilitate analysis and decision-making. Several methods exist already to evaluate dam stability and to estimate ligament and cracking length at the dam-foundation interface, such as the load-increasing method and the strength reduction method. The load-increasing method involves raising the water level or increasing water density. The strength reduction method involves reducing the internal friction angle or reducing the cohesion at the dam-foundation interface. These methods are applied by incrementing the parameters of interest and by multiplying these parameters by a coefficient K to find the critical case when the sliding safety factor is equal to one or when the cracking at the base is significant to threaten the stability. To analyze these methods and their effectiveness, they are tested and compared on a 17.9 m high gravity dam using the gravity method for structural analysis. Some comparisons are made with the finite element method to highlight some limitation of the gravity method. The increasing water level method proves to be interesting, as it is relatively easy to apply. However, simplifying assumptions must be made for overtopping conditions. Results obtained when water density is incremented are not obvious, making this method not recommended. The strength reduction method gives good results and is easy to use.