Drawdown scenarios imposed to an earth dam after a strong earthquake

Establishing the maximum drawdown rate that may safely be imposed to an earth dam is crucial because a typical practice soon after the occurrence of a strong earthquake is that of emptying the reservoir to check the possible damag-es occurred to the embankment or, simply, in the unjustified believe to proceed at the safest. The unfavourable effects of earthquake and drawdown may thus critically sum up as both the dam and the reservoir slopes are subjected to two potentially critical events. Dam stability soon after the drawdown may be ascertained in terms of global safety factor (FOS), considering different drawdown levels and rates. To better characterize how the seismic-induced changes in pore water pressure and stress affect the computed FOS, a drawdown scenario was also analysed in absence of a former earthquake stage. For some drawdown rates, the seismic effects are able to induce a significant drop in FOS during the drawdown stage up to values dictating global instability of the embankment slopes.