Seismic simulation and base sliding of concrete gravity dams

A simplified procedure to estimate possible base sliding of concrete gravity dams induced by an earthquake is proposed on the basis of results obtained by parametric analysis. A simple mechanical model is developed to take into account the most relevant parameters influencing seismic response such as dam-water and dam-foundation interaction. In order to catch base residual displacement, a threshold value for the sliding foundation resistance is fixed. The dam is modelled as an elastic linear single degree of freedom system. The hydrodynamic effects of the water in the reservoir are taken into account with generalized supplementary mass and force as well as by adding supplementary damping. The foundation resistance is modelled with the Mohr-Coulomb criterion including a frictional and a cohesive component and the presence of a passive wedge resistance is also considered. A comprehensive numerical analysis of the response of concrete gravity dams subjected to several natural earthquake records relative to events mainly happened in Italy is carried out to estimate base residual displacement. Different parameters are considered in the analysis such as dam height, foundation rock parameters, water level, seismic intensity. As a result a simplified methodology is developed to evaluate base residual displacement, once known dam geometry, response spectrum of the seismic input, and the soil characteristics. The procedure permits to assess seismic safety of the dam with respect to base sliding, as well as water level reduction necessary to render the dam safe enough.