Study on Seismic-spectrum Characteristics for 300m-grade Earth-Rockfill Dam

Combining with Shuangjiangkou Dam with height of 312 m, we make a study on the spectrum characteristics of rockfill dams with core wall adopting the dynamic model which reflects vibration-hardening character of coarse rockfill materials. The rationality of the model and parameters is verified by comparing calculated values with measured values of natural vibration period and shear-wave velocity. In the paper, some conclusions are obtained as below. When the elastic modulus of the foundation is 50 times lager than the modulus of the dam, the effect of computing foundation range to seismic response of the dam could be ignored. The vibration modes of high earth dams are dense and the natural period of high-order vibration mode is closer to the eigenperiod of bedrock, so more vibration orders will be excited. As a result, more exponent numbers of vibration orders will be considered when superposition method of mode of vibration is adopted. Earth dams have obvious filtering effect to seismic waves input from foundation and only components that are closer to basic natural vibration period can be magnified obviously due to strong resonant excitation. The higher a earth-rockfill dam is, the farther natural vibration periods of the dam´s main vibration modes are from eigenperiod of bedrock, so resonance is hard to occur, which is the reason why high earth-rockfill dams built on bedrock have good seismic performances.