Assessment of seismic behaviour of large concrete dams by means of geomatic techniques and finite element modeling

The safety and efficient maintenance of dams are primary aspects in the management of such strategic works. The need to combine the security with the containment of maintenance costs directly linked to the service life of the structure, requires innovative approaches beside traditional methods. In this respect, the limited accessibility of large dams does not facilitate the use of traditional survey techniques, although a reliable terrestrial survey is still necessary, the use of Unmanned Aerial Vehicles (UAV) is well suited for this purpose. The aim of the present study is to provide a reconstruction procedure of a high detail FE model of a dam starting from an integrated UAV survey useful for a predictive and proactive maintenance of the dam system. In particular, the “Structure from Motion” (SfM) technique can be used for the reconstruction of 3D objects from 2D images. Therefore, after an integration of the UAV dense point cloud with pre-existing data sets such as design geometry, Digital Elevation Model (DEM) of the area and bathymetry of the lake, a 3D solid reconstruction of the whole dam system is possible. Important elements of the structure such as spillway, vertical joints and pulvino foundation joint and of ancillary works such as stilling basin and weight blocks are reproduced. In order to study the influence of joint modelling on the dynamic behaviour of the structure, three models have been analyzed: monolithic m., surface-to-surface joint m. and solid element joint m.. All simulations take into account the structure-foundation interaction by means of a rock mass solid and the fluid-structure interaction by means of acoustic elements. Modal analyses are therefore performed in order to obtain the dynamic properties of the models and to identify the representation which fits better with the real dynamic records (e.g. vibrodyne test, ambient vibrations). Subsequently, linear elastic dynamic analyses are performed to calibrate the damping coefficients of rock mass and structure. Finally, non-linearity is introduced in the joint elements performing non-linear dynamic damage analyses under severe earthquakes and, varying the water level, the damage distribution is investigated. The inclusion of vertical construction joints into finite element models of dams allows us to verify the behaviour of such real discontinuities under severe seismic events and therefore to verify the seismic vulnerability assessment of the whole structure.