Research on hazard assessment and mitigation measures of landslides induced by large-scale earthquakes on cut and filled slopes in densely-populated residential areas in big cities

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Three component seismometers and pore water pressure meters were monitored which were installed in the boreholes in the test site of densely-populated area of Hino city of Tokyo metropolis. Especially dynamic response of up-down component of the pore water pressure showed high correlation with remote large-scale earthquake. Ring shear tests of the soil samples obtained from the core samples of boreholes showed that saturated soils of filled valley with shallow ground water table is susceptible to generation of excess pore pressure at seismic condition. It means that those filled valley grounds are vulnerable to rapid landslides at the upcoming large earthquakes beneath the Tokyo metropolitan area.Field investigation was organized to the 2004 Mid-Niigata Earthquake epicenter area where numerous landslides were induced. Among them, Higashi-Takezawa landslide which showed rapid and long runout movement on a gentle slope and formed a landslide-dam by filling a major river, was focused beca … More use reactivated landslides rarely ran rapidly. Soil samples were taken from the exposed sliding surface and ring shear tests were conducted under undrained condition and by applying real seismic acceleration monitored nearby. Big excess pore water pressure generation and accelerating shear displacement were observed, which could explain its rapid motion mechanism. In addition, field investigation of the landslide in Leyte Island of Philippine which occurred in February and killed more than thousand people. Ring shear tests on soil samples obtained in the field proved that the landslide could be induced not only the ground water rise due to heavy rainfall of 5 days prior to the slide, but also triggered by a small earthquake which occurs just before the initiation of the landslide movement.Geotechnical landslide movement simulation which was developed by Sassa, was applied to the test sites in Hino-city and its adjacent Hachioji-city, as well as Higashi-Takezawa landslide site using dynamic characteristics parameters obtained by the ring shear tests as well as high-resolution topographic data obtained by airborne laser scanner. Results on Higashi-Takezawa landslide matches well the actual landslide runout area. Assessment of landslide runout areas, namely the hazardous areas were identified based on the measured soil characteristics and computer simulation using those values for the two test sites of Hino-city and Hachioji-city by the simulation output. Less