EVALUATION OF THE MATERIAL PROPERTY AND SEISMIC PERFORMANCE OF A ROCKFILL DAM DURING LARGE DOUBLET EARTHQUAKES

抄録

 The relationship between the shear modulus and shear strain of embankment materials is evaluated based on earthquake records. When the average shear strain of a dam body is less than approximately 2.0×10^-4, the decreased stiffness of the embankment materials can be promptly recovered. However, when the shear strain exceeds 1.0×10^-3, one week or more may be necessary for the stiffness to be recovered. Using the evaluated nonlinear properties, the behaviors of the Aratozawa dam during an assumed large doublet earthquake are investigated through numerical analyses. The results indicate that the change in the dynamic characteristics of the dam in response to the first event considerably influences the dynamic behaviors of the dam during the second event. In addition, a procedure to evaluate the seismic performance of rockfill dams during doublet earthquakes is proposed. In this approach, the variation in the material properties in the first and second events is considered. The final residual subsidence of the dam is predicted by summing the sliding displacements caused by each earthquake and subsidence related to the shaking and rear-rangement of soil particles. Furthermore, as a precautionary measure for assumed large doublet earthquakes, after a dam experiences a large earthquake, it is recommended that the reservoir be adjusted to a safe water level and maintained at that level for at least one week as an emergency response measure.