Nonlinear seismic response of earth dams due to dam-reservoir interaction

Field data show that the seismic response of a dam with a full reservoir is different from a dam with an empty reservoir. This is due to“dam-reservoir interaction” (DRI), which is related to the asynchronous vibration of the dam and reservoir domains. It was for long considered that DRI effects are important for concrete dams and insignificant for earth dams. This was based on findings considering mainly dam crest accelerations, which for earth dams were indeed found to be insensitive to DRI. However, other aspects of the response of earth dams, such as the deformation characteristics, should also be considered to fully characterise the seismic dam response. Therefore for a more complete study of the DRI effects on the seismic response of earth dams one should also consider the induced seismic shear stresses and strains, along with the magnitude of reservoir hydrodynamic pressures. This study considers a well-documented case study, the La Villita earth dam in Mexico, for which relevant field measurements are available allowing the development of a well-calibrated numerical model. A series of static and dynamic nonlinear finite element analyses are performed which consider the impact of the reservoir domain on the dam response. It is shown that although earth dam crest accelerations are indeed insensitive to DRI, the actual dynamic soil behaviour can be severely affected, developing large values of seismic shear stresses and strains within the dam body. This study highlights the importance of accurately considering DRI when assessing the seismic performance of earth dams.