Aftershock often takes place in the wake of a main shock

and the cumulative damage effect of dam structure can become significant after several aftershocks. To explore the deformation and stability of a gravity dam with a complex foundation under the combined effect of main shock and aftershock

a dam section #A of a large-scale hydraulic project close to Wenchuan-epicenter is adopted for a case study. Firstly

only the main shock only is considered

which is simulated using the pseudo-static method in the geomechanical model test

and through experiments the deformation characteristics and the final failure pattern of dam section #A and foundation are studied. Then based on this

the time history analysis is performed

and the combined effect of main shock and aftershocks is analyzed using the 3D FEA software ANSYS. The results show that the model testing results are consistent with calculations. Under the effect of main shock

both the dam and foundation generate large deformation; and the final failure pattern of dam section #A is obtained. Under the combined effect of main shock and aftershock

the cumulative deformation effect of dam and foundation becomes more significant

and the displacement is significantly larger than that induced by the main shock only. The maximum displacement amplification of dam is about 37% which has a significant impact on the stability of dam and foundation. Therefore

the gravity dam on complex foundation in highly seismic region should take into account of the combined effect of main shock and aftershock so as to ensure the project security.