Avalanche action on rigid structures: Back-analysis of Taconnaz deflective walls' collapse in February 1999

Knowledge about action undergone by an obstacle impacted by an avalanche is still insufficient to allow civil engineers to design really efficient and resistant structures. The main difficulty is to take into account the mutual interactions that occur between the structure and the flow and the influence of the obstacle on the avalanche action itself. An original back-analysis principle is proposed to obtain information on avalanche action from real destructive event and to ensure that the result is effectively what is undergone by the structure and not only what could be generated by the phenomenon. In that way, the destruction of two deflective walls in Taconnaz site by the 11th of February 1999 exceptional avalanche is studied with several parts: firstly, a large site investigation program is conducted to gather observations including material specimen's tests and to exhibit two collapse scenarios. Then, laboratory experiments are performed to confirm failure mechanisms. Finally, numerical simulations used a rigorous three-dimensional finite elements model and a realistic representation of the concrete behaviour to evaluate the effective resistance of the structures under different conditions, including quasi-static, cyclic and dynamic influences.