Journal of the Japan Landslide Society
Online ISSN : 1882-0034
Print ISSN : 1348-3986
ISSN-L : 1348-3986
Original articles
Mechanism and Characteristics of Landslide Occurrence at Hishikari Town, Kagoshima Prefecture
Bungo TAMADANaomichi YOKOYAJunji FUKUDAMotoyuki SUZUKI Motoyuki SUZUKITetsuro YAMAMOTO
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JOURNAL FREE ACCESS

2008 Volume 44 Issue 5 Pages 292-301

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Abstract

This paper describes the mechanism of occurrence of a landslide with flow-type collapse at Hishikari town, Kagoshima Prefecture, Japan.
The geological structure of this area is as follows:
(1) Collapse soil is on the bedrock (weathering tuff breccia) and is about 3m thick.
(2) The inclination of the bedrock is 27C.
(3) There is transported cohesive soil along the boundary between the collapse soil and bedrock.
When there is a friction-type sliding surface in transported cohesive soil, weak faces are composed of these two parts. When the total length of the sliding surface is ls and the length of the friction-type sliding surface is lf, then the "weak face ratio" Rf is expressed by Rf=lf/ls. The weak face ratio is generally about 0.05 for a stable slope, but increases when the debris on weak faces is repeatedly saturated by rainfall, and the ratio becomes unstable when it exceeds 0.2.
When rainfall exceeds QEP, creep failure of the weak faces occurs, so QEP is given by QEP=100·hs, where QEP is an effective preceding rainfall, and hs is the depth of weak faces.
When a landslide of this type occurs, sliding debris flows as groundwater flows into the sliding debris.

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© 2008 The Japan Landslide Society
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