The safety assessment of Campotosto Lake dams following 2016-2017 seismic sequence in Central Italy. Focus on Poggio Cancelli embankment dam

The Campotosto Lake is one of the biggest reservoirs of Europe, with a storage capacity exceeding 200 million of m3. The natural original lake was confined with three large dams owned by Enel. In the recent past, the lake and the dams have been subjected to a series of seismic events known as the seismic sequence of L'Aquila in 2009 and the seismic sequence of Central Italy in 2016-17. Following the last one, Enel promptly decided to temporarily lower the water level to carry out surveys, measurements and automatic monitoring activities. Based on available data, in order to verify, ensure and asseverate the safety conditions of the dams and the lake’s slopes, a series of multi-disciplinary studies and in-depth analysis were specifically conducted. Detailed studies were developed for the Poggio Cancelli embankment dam: geotechnical surveys, geophysical in situ tests and “advanced” laboratory tests in order to define at best the foundation soil characteristics, thus reasonably excluding the liquefaction risk applying sophisticated methods of analysis. Moreover, InSAR analysis allowed to retrieve the displacement history of the sites and confirmed the topographic measurements taken before and after the earthquakes. Displacement data, together with the real accelerograms recorded at the dam toe were used for a back analysis of the settlements by means of a FEM model of the dam. With this validated model, it was possible to simulate the seismic response of the embankment in the catastrophic scenario represented by the worst expected earthquake at the site. However, recent and important research contributed to establish the position and associated potential magnitude of the Campotosto fault. They indicate that the seismic scenario adopted by our analysis is precautionary, therefore our results are conservative. Seismic assessments on the other dams and InSAR analysis of the slopes surrounding the reservoir were also carried out. All these studies were concluded in 2020 showing good results and satisfactory safety factors, allowing Enel to set up again Campotosto reservoir to normal water levels.