New Evaluation Method for Liquefaction of Ground Using Dynamic Liquefaction Analysis Method and Its Application

Abstract

Nankai megathrust earthquakes are expected to occur with a return period of approximately 90–200 years along the fault of the Nankai Trough. Because they are interplate earthquakes, it is predicted that they will cause heavy liquefaction damage as a result of the long duration of their ground motion, especially around bay areas with soft deposits. In this study, a numerical analysis was performed for the ground in Osaka City with a hypothetical earthquake in the Nankai Trough region. In the numerical simulation of the dynamic behavior, a liquefaction analysis program was used. To quantify the degree of liquefaction at certain points, an index, named the liquefaction risk index (LRI), was defined and obtained by the weighted integration of the effective stress-decreasing ratio (ESDR) with respect to depth. Moreover, the LRI values were evaluated by data from the 1995 Hyogoken-Nanbu earthquake. It was found that the obtained LRI values were greater than 6.0 for the points at which heavy liquefaction damage had occurred. From the numerical results, the risk of liquefaction was evaluated with these LRI values.