Seismic Performance of Small and Medium-Sized Homogeneous Earthen Dams Considering Valley Site Effects in Large-Scale Shaking Table Tests

Many existing small and medium-sized homogenous earthen dams (SMHEDs), which were constructed world-wide before the establishment of seismic design codes, are prone to fail when subjected to earthquakes. The geologic condition and shape of the valley sites where SMHEDs are located have an important role in the seismic performance of the dams. In this paper, large-scale shaking table tests were conducted to analyse the seismic responses of the SMHED considering valley site effects. A geologic model with a 'stiff' dam built in a 'soft' valley was employed to simulate the inappropriate site selection and insufficient treatment of the soft soil layers of valley sites during the construction of SMHEDs. The effects of the spectral characteristics of the dam and the frequency components of the input motions on the seismic responses of the SMHED are analyzed in combination with frequency-domain analysis. The results indicate that the local dominant frequencies at different positions of the SMHED exhibit differences due to valley site effects. Under the input motion with different predominant frequencies (FP), the local dominant frequency differences along the dam crest lead to different distribution patterns of the acceleration response along the SMHED crest, and consequently, different damage modes. Under input motions with FP lower than the dominant frequency of the SMHED, the combined damage of collapses and cracks at the end of the SMHED crest tends to develop into massive sliding. Furthermore, recommendations for the aseismic and reinforcement design of SMHEDs are given.