|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1998 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1997 : ¥1,400,000 (Direct Cost : ¥1,400,000)
In accordance with the research plan the head investigator first derived the slide velocity that causes instability in the base of a landslide. As a result it was found that the slide velocity threshold for instability is on the order of 10 m/s that is easily attained by landslides(Kobayashi, 1997).
The cooperative investigator, on the other hand, surveyed debris avalanche deposits at several sites including Iwasegawa, Kaida, and Mt. St. Helens and found evidence for a boundary layer in the bottom of the debris-avalanche deposits. He also found that the flow mechanism of the debris avalanches, at least in the final stage, may be seen as plug flow(Takarada, 1999).
Cooperative study by the head and cooperative investigators encountered a difficulty, since the cooperative investigator left Japan for study during the term of the project. However, they exchanged information and views by E-mail frequently and the research was promoted greatly (a part of the mails included in the main report).
Along with original study of the project the head investigator made a review of the movement mechanism of large rock avalanches, and examined the validity of his own hypothesis(Kobayashi, 1999).
It may be concluded that mechanism of a rock avalanches should be divided into those in the developing , flowing and depositing stages ; i.e. no unique mechanism can work through the whole stages. In this respect our hypothesis, basal guided wave theory, also cannot be an exception and it should be used only in the accelerating stage till the slide velocity exceeds the instability threshold.