Analysis of the mechanism of embankment failure during the 2007 Chuetsu Oki Earthquake, Japan

Abstract

This article presents the results of an analysis conducted to investigate the mechanism of embankment failure during the 2007 Chuetsu Oki earthquake (MJMA=6.6) that occurred in Niigata Prefecture, Japan. Data from field investigation were utilized to reconstruct a cross-section of the slope prior to the earthquake, and to estimate the in-situ properties of soil from the landslide mass. It was found that the failure plane formed in a saturated layer of sandy soil near a boundary with bedrock. Laboratory investigation, including a series of triaxial compression tests, was conducted to evaluate the liquefaction potential of the soil as well as to provide a basis for numerical analysis. Slope stability analysis performed on the basis of FEM procedure for the conditions existing before the earthquake yielded a safety factor of 1.18, indicating that the slope was amply stable prior to the earthquake. Results of undrained cyclic loading triaxial tests in conjunction with seismic response analysis of the embankment revealed that liquefaction of the saturated sand could have occurred during the earthquake. Furthermore, liquefaction analysis conducted on the basis of SPT-data provided more evidence supporting this hypothesis. Considering the obtained results, slope stability analysis was conducted for the conditions existing after the earthquake. The computed safety factor of 0.88 suggested that the stability of the slope was significantly undermined by the earthquake.