Earth dams: Damage mechanisms and limit states in seismic conditions

The paper summarizes the main damage mechanisms suffered by earth dams under both strong earthquakes and normal operation to identify the limit states that should be taken into account for dam seismic safety assessment. In addressing limit states, a distinction is made between seismic and post-seismic stages. The limit state of global instability under the effects of inertial loads is considered both in the seismic stage, taking into account the favourable contributions of ground motion asynchronism and during the post-seismic stages, when excess pore water pressures induced by seismic shaking and by a possible rapid drawdown could affect dam behaviour. The limit state of dam freeboard loss is then dealt with, showing the importance of estimating settlement rates during the seismic and post-seismic stages. Third, the limit state of water-tightness loss is discussed with reference to seismic-induced strain concentration or stress changes. Finally, the risk of liquefaction within the embankment or in the foundation is considered, discussing how the phenomenon could be affected by changes in particle grading possibly experienced by coarse-grained materials during normal operation of the dam.