Static and seismic analysis of an arch-gravity dam
Formulator: Frédéric Andrian (Artelia), Pierre Agresti (Artelia), Geoffrey Mathieu (Artelia)
The Janneh dam (RCC, 157 m high), under construction in Lebanon, was initially designed as a straight gravity dam. Due to seismic reasons, the layout of the dam has been arched in order to prevent from an unacceptable sliding of the dam on its foundation. Moreover, for the purpose of concrete saving, the downstream face of the dam has been vertically truncated.
Arch effect is triggered in the dam owing to its curvature, even for Normal Water Level. The arch effect offloads the central block and overloads the bank blocks. Therefore, the bank blocks exhibit an opening at the upstream toe as soon as the reservoir is impounded. Such behavior is generally not tolerated for a straight gravity dam.
Moreover, as the downstream face is vertically truncated, the 2D section of the central block does not satisfy the generally adopted stability criteria for straight gravity dams. The stability of the dam relies consequently on its 3D behavior.
Due to this very specific behavior, the excavation of the dam has been provided with a converging geometry as to guarantee that the arch stress is as perpendicular as possible to the excavation. In addition, the design of its components needs to be accommodated. The drainage gallery and the grout curtain needs to be moved toward downstream, avoiding the region with upstream toe opening. Otherwise, the drainage is likely to be saturated and the grout curtain bypassed by the water. However, if placed too far downstream, their efficiency decreases.
The seismic behavior of the dam is also to be checked. The converging geometry of the excavation prevents from any overall sliding toward downstream under the Safety Evaluation Earthquake. However, the dam and most of its appurtenant structures shall remain functional after the occurrence of the Operating Basis Earthquake.
The numerical analysis of this dam is proposed as theme B of the 14th ICOLD Benchmark Workshop and will comprise static as well as seismic calculations.
The calculations to be carried out will follow a progressive approach: the subsequent stages are of increasing complexity.
For the static analyses, the first stage considers a linear analysis with the uplift to be considered as a post-treatment parameter. The final stage considers a non-linear analysis with a coupled hydro-mechanical approach at the opened regions of the dam / foundation interface.
For the seismic analyses, the stages range from pseudo-static analysis to non-linear time history analyses with increasing complexity of simulation of the dam-reservoir-foundation interaction.
The simplest stages are mandatory to report if participating to theme B. The more complex ones are optional.
The participants are requested to provide with results corresponding to a few parameters described by the formulators. The formulators will provide with the input parameters to be used in the models as well as examples of meshes and dxf geometries.
The aim of the theme is to highlight the possible assets brought by more advanced modelling approaches for the design and the safety of this type of dams.
The instructions and data can be downloaded from the following link