The paper describes the case-history of the Beauregard dam (Italy), a concrete arch-gravity structure 132m high built between 1951 and 1958 on the Dora di Valgrisenche River. The design reservoir volume was about 70Mm3.The geological and geotechnical investigations carried out since the dam construction and deepened in the last decades have underlined that a Deep-Seated Gravitational Slope Deformation (DSGSD) is located on the left slope.

Since the first fillings of the reservoir, the interaction between the DSGSD and the dam was recognized to have relevant implications on the dam structural safety. For that reason, the Italian Dam Authorities in 1969 prescribed a limitation of the reservoir level with a corresponding reduction of its volume to 6.8Mm3, about 1/10 of the initial design volume.The investigations, which include a detailed analysis and thorough interpretation of the monitoring data over a time span of more than 50 years, have allowed to gain insights into the understanding of the DSGSD behavior and its interaction with the dam.

The interpretation of the effects of the slide movements against the dam, the forecast of the future possible trends and the choice of the design solution to guarantee the long-term safety operation of the dam – consisting in the demolition of the upper part of the structure in order to drastically avoid the foreseen occurrence of large deformations and displacements in the dam body associated to the DSGSD movement – have been performed making resort to complex numerical modelling activities that are widely described in the paper.