Kita-Uebaru natural rock slope failure and its back analysis

A large landslide occurred in Kita-Uebaru (or Asato) area of Nakagusuku village in Okinawa Island (Japan) on 10 June 2006 after a rainy period of about 9 days. The total rainfall was 126 mm from June 8 till the time of the landslide this period. This landslide destroyed several buildings and roads, and the total travel distance of the landslide was about 110 m. In this article, the authors were concerned with the initiation conditions of Kita-Uebaru landslide and post-failure motions of the landslide body. The observations made in the landslide area, structural geology analyses and outcomes of geotechnical investigations are described first. Then, possible causes of the landslide are investigated through back analyses using as inputs the geological structure and the strength properties of planes of discontinuities involved in the sliding processes. The final part of the article is concerned with the simulation of post-failure motions of the landslide body. The results of the investigations and back analyses indicate that the failure plane was bi-planar and the heavy torrential rainy period for about 3 days was the main cause of initiation of the landslide. The mechanical model presented in this article was capable of capturing the overall features of the landslide body following the initiation of the failure.