LARGE-SCALE SHAKING TABLE MODEL TESTS ON DYNAMIC CHARACTERISTICS AND ACCELERATION DISTRIBUTION OF LANDSLIDE DAMS

At least 257 landslide dams were formed by Wenchuan earthquake in 2008. The aftershocks occurred after the major quake may influence the safety of those landslide dams. Dynamic characteristic parameters, including natural frequency and damping ratio,and distribution of acceleration amplification factor are the focus of the research of landslide dams. This paper presents the studies of large-scale shaking table tests on the dynamic characteristics and the acceleration distribution of landslide dams under aftershocks. The natural frequency,the damping ratio and the distribution of acceleration amplification factor of a model dam and their influencing factors are studied. The dynamic characteristic parameters of prototype landslide dams are calculated according to the similarity law. Two groups of shaking table tests are conducted to simulate the behaviors of two types of landslide dams:one with small particle size having the cohesive materials(dam I) and the other with large particle size not having the cohesive materials(dam II). The shaking table tests were conducted under different earthquake waves, different peak ground accelerations(PGA) and different water depths. The following conclusions are drawn:(1) The model dams have stable X-directional and Z-directional natural frequency and damping ratio.(2) Earlier shaking makes the natural frequency to decrease and the damping ratio to increase. The natural frequency of dam I is smaller than that of Dam II. The effects of water depth on the natural frequency of the two types of dams are different.(3) In vertical direction,acceleration amplification factor increases from the base to the top of the dam. The maximum accelerations occurred mainly on the top of the dams. In horizontal direction,the maximum accelerations occurred on the upstream and downstream surfaces of dam slopes,i.e. the surface amplification effect,which showed that the dam slope surfaces were prone to fail under earthquake action.(4) The earthquake waves with the predominant frequency close to the natural frequency of landslide dams induce the most prominent acceleration response. The earthquake in Z direction made the amplification factor of acceleration in X direction increase. The acceleration amplification factor decreases as PGA increases.