Calibration of finite element models of concrete arch-gravity dams using dynamical measures: The case of Ridracoli

Accurate and reliable predictions of the dynamic behaviour of dams is essential to ensure their correct management and the safety of the downstream population. In this context, structural monitoring and testing procedures for their dynamic characterization are essential tools for the calibration of numerical models of dams. This paper presents some results of an ongoing research program aimed at an accurate definition of the geometric and structural properties of a large arch-gravity dam: the Ridracoli dam in the Emilia-Romagna region, Italy. In the first part of the research, a detailed survey carried out by an Unmanned Aerial Vehicle has allowed the detailed reconstruction of the three-dimensional geometry of the structure. The dense point cloud, as provided by the aerial survey, has been the base for the definition of a high-fidelity finite element model, including the dam, the surrounding rock mass, with a detailed reconstruction of the site topography, and the reservoir water, whose dynamic interaction with the structure is modelled by means of acoustic elements. A large program of structural monitoring, including a number of vibration tests, has been performed on the Ridracoli dam during the last thirty years. The dynamic monitoring system includes accelerometers, located in the structure and in the foundation rock mass, strain gauges and hydrodynamic pressure cells. The forced vibration tests were carried out in correspondence to the maximum water level, in order to identify the dynamic characteristics of the dam. The mechanical properties of the dam material and of the foundation rock are calibrated by comparing model predictions with the results obtained from vibration tests and from acceleration recordings acquired under recent seismic events, considering the actual water levels registered during the tests. The finite element model obtained will allow the simulation of the seismic performance of the dam under different design earthquakes. The assessment of the effects of the reservoir level and of the vertical joints on the dynamic response of the structure will be analysed.