Laouzas dam: behavior of a thin concrete arch dam located in a wide valley and foundation stability improvement

Through the example of Laouzas dam owned by Electricite de France, this paper presents the mechanical behavior of a thin concrete arch dam located in a wide valley. From the first impoundment of the reservoir, this dam was affected by an opening of the rock-concrete interface near the central cantilevers. The reinforcement of the monitoring system, in particular the installation of piezometers at the downstream part of the dam-foundation contact, enhanced the progression of pore pressure in this zone beyond the generally admitted hypotheses. In order to explain such situation and to evaluate the consequences, finite-element analyses taking into account hydro-mechanical modeling were performed. They helped in understanding the observed phenomena and describe the conditions of the damfoundation thrust transmission towards downstream in the central part of the foundation. On Laouzas dam, after study of different solutions of reinforcement, local foundation reinforcement downstream of the central blocks was decided and implemented.