Abstract
An unprecedented local downpour occurred in Niigata Chuetsu region on 13 July 2004. The total amount of rainfall reached 250 mm in an area 20 km in a north-south direction and 100 km east-west direction including Sanjo, Mitsuke, Nagaoka and Tochio cities. The Niigata Prefectural Government have reported that the heavy rainfall caused 11 dike breaks and over 300 landslides. Consequent damage included 15 deaths (2 out of 15 were killed by landslides) and over 26,000 houses flooded. This paper first presents an outline of this disaster. A detailed investigation was carried out on a dike break and a natural slope failure to clarify the failure mechanisms. Then a series of direct and ring shear tests was conducted to examine the shear strength considering moisture content and existence of a discontinuity plane. Strength parameters obtained from the experiments were used for slope stability analyses. Finally, new simple analytical and estimation methods using an unsaturated seepage and slope stability analyses are presented.
