Stability Analysis of an Overtopped Spillway Using Computational Fluid Dynamics: Fid-Bau Portal

Stability Analysis of an Overtopped Spillway Using Computational Fluid Dynamics

Freitas, M. / Léger, P. / Pedroso, L.

Concrete gravity dams are usually designed to be non-overflow sections. However, due to global warming, flood events have become more frequent and more intense, possibly surpassing the amount of flow for which old structures were designed. Estimating the hydrodynamic forces acting on a dam or spillway during a flood is challenging. Typically, either simplified analytical solutions or complex and expensive physical models have been used. However, Computational Fluid Dynamics (CFD) is now an attractive alternative that can yield more accurate results than simplified analytical solutions while being cheaper and faster to implement than physical models. This paper presents a back analysis of the Chute Garneau concrete spillway during the Saguenay flood of 1996. During this event, the spillway bridge, which is 6.35 m high, was overtopped by about 2 m. There was a significant accumulation of floating debris that got stuck on the gates lifting structure. Some gates could not be opened because of ongoing rehabilitation work. Despite the severity of the flood, the structure survived the event. Herein, a CFD analysis is performed to obtain the hydrodynamic pressure fields on the structure under different scenarios, such as with gates open, closed, partially closed and with accumulation of floating debris. Then, the hydrodynamic pressure is integrated to obtain the resultant forces which are used as input to a stability analysis using the gravity method. It is shown that a small amount of cohesion and tensile strength on the rock-concrete interface, both very uncertain parameters, were mobilized to keep the structure stable.