Numerical Analysis on Seismic Response of Shiziping Earth-rockfill Dam

The Shiziping hydropower station locates at the Li county in Sichuan province in China. The distance from the epicenter of Wenchuan earthquake to dam site is only about 55km. It is a zone with high seismic intensity, so the safety of dam during earthquakes is of great importance. Three dimensional dynamic finite element method (FEM) analysis is employed to study the dynamic behaviour of the dam during earthquakes. The initial stress fields of the soil elements are computed by static calculation, in which the nonlinear elastic Duncan-Chang constitutive model has been adopted to simulate soil behavior. In dynamic calculation, the soil is considered to be viscoelastic material and the equivalent linearization dynamic constitutive model is also applied for simulation. The viscous-elastic boundary is set along the model boundaries. The results indicate that the acceleration response is symmetrical along dam axis, which decreases gradually from the center of valley to two banks. The acceleration response on top of dam at the center of valley is the largest. The maximum acceleration responses in X direction under seismic waves A and B are 3.61m/s(2) and 5.64m/s(2), the amplifications of which are 2.47 and 2.11, respectively The dynamic shear stress is increased as the distance from dam face increases. The maximum dynamic shear stress response in overburden is about 400kPa. The minimum dynamic stresses under seismic waves A and B are -1.10 MPa and -1.60 MP a, respectively The dynamic tension stress in grouting gallery is very large, so the local tension crack is possible. The vertical maximum permanent deformation occurs at the top of dam near the middle of riverbed. The maximum vertical permanent deformations under the action of seismic waves A and B are 44.5cm and 60.4cm, respectively. The shear stress varies during the process of earthquake, so the safety factor of dam slope is a function of time. The minimum safety factor of upstream dam slope under seismic wave B is 1.19 and that of downstream dam slope is 1.06. All the safety factors are greater than 1.0, thus the dam slope is steady during earthquake.