The geotechnical disaster in Nakadoori area and Iwaki area of Fukushima Prefecture

- Failure and deformation of embanked ground and natural slope, liquefaction -

Abstract

This report describes the results obtained by investigating about the effect of a seismic action, geographical feature and ground structure, material properties, etc. on the failure of embanked ground and natural slope generated in Nakadori area and Iwaki area of Fukushima prefecture. As for the damage of the developed land, the geographical feature occurred at the valley filled embankment and the embankment reclaimed on the water pond. The material properties of the land for housing lots at Fushiogami of Fukushima is volcanic cohesive soil and the properties at the other land is fine sand with non-plastic. The common feature is found with the flow failure of the embankment with volcanic sand generated in Tohoku district on the recent earthquakes. Either the landslide or the failure of natural and cut slope occurred mostly in the southern part area of Nakadoori district. The landslide has the moving body which consists of unbounded pyroclastic sediments, and failure generated on the surface of the slope with the pyroclastic flow sediment which is the bedrock in this area. The failure mechanism of landslide is a compound slide which has more than two slip surfaces. The upper part of the landslide is caused by progressive failure due to the strong earthquake motion. The lower part of slide is generated by the reduction of the shear strength.