A study on the seismic segmentation method of levee using the natural frequency of multiple layers

Abstract

The Levees of Shinano River were subjected to many damages at Niigata Chuetsu Earthquake in 2004 as well as Tohoku-Pacific Ocean Earthquake in 2011. The damage of levees depends not only on the distance from the epicenter, but also on the soil profile of levee and its foundation. In this study, we classified the damage of levee into five types, and investigated the relationship the geological categorization and the seismic characteristics of the levee with the damage types. The natural frequency for multiple layers and the shape of transfer function were adopted as the seismic index, because the natural frequency can be express the seismic stiffness of levee. To obtain natural frequency of multiple layers, we carried out the linear elastic analysis based on multiple reflection theory using the results of standard penetration and laboratory soil tests. Those investigations of levee have already performed at each 1 km, for every main rivers managed by MLIT, therefore the new investigations are not required. However, the interval of 1 km is not enough for management length in Japan sea side region, because of its geological complexity compared with the Pacific Ocean side. To specify the representative levee length for one borehole logging, the geomorphologic data was considered. To estimate the damage rank, the influences of magnitude of ground motion should be considered. In this study, the multiple linear regression analysis, which the base acceleration, the natural frequency and the shape index of transfer function were adopted as dependent variables, and its explaining variable was damage rank, was performed to prediction of damage rank.