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GEO- AND HYDRO-MECHANICAL EVALUATION OF SLOPE FAILURE INDUCED BY TORRENTIAL RAINS IN NORTHERN-KYUSHU AREA, JULY 2009


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タイトル: GEO- AND HYDRO-MECHANICAL EVALUATION OF SLOPE FAILURE INDUCED BY TORRENTIAL RAINS IN NORTHERN-KYUSHU AREA, JULY 2009
著者: Kasama, Kiyonobu / Jiang, Yujing / Hiro-oka, Akihiko / Yasufuku, Noriyuki / Sato, Hidefumi
発行日: 2011年 9月 2日
出版者: 地盤工学会 / Japanese Geotechnical Society
引用: SOILS AND FOUNDATIONS, 51(4), pp.575-589; 2011
抄録: Torrential rainfall in mid-July 2009 triggered numerous geodisasters such as slope failure and debris flow in Chugoku and Northern Kyushu areas of Japan. A number of slope failures and debris flows occurred in Yamaguchi and Fukuoka prefectures resulting in extensive damage to human life and infrastructure. One of the most serious geodisasters included a slope failure followed by debris flow at Sasaguri-machi and Fukuchi-machi, Fukuoka prefecture, Japan. This paper summarizes the results of geotechnical investigations on the geodisaster sites in Fukuoka prefecture. The geotechnical investigation included determining a series of grain size distributions, consistency limits and conducting direct box shear tests for collapsed soils collected at six disaster sites. The generation mechanisms of slope failure followed by debris flow were also investigated by analyzing the precipitation, topography, geology, and strength properties of the collapsed soils. Moreover, slope deformation and stability analyses were coupled with an unsaturatedsaturated seepage analysis to investigate the slope failure mechanism. The main findings from the study are summarized as: The physical properties, such as the grain size distribution, the plastic limit and liquid limit of collapsed soils, are summarized and compared with the results of other failure slopes in the literature. The collapsed soil was characterized as being a well grained soil (the uniformity coefficient >50) and highly weathered (the ignition loss >5z), however, with regard to the liquid limit and plastic index, there were no remarkable findings. The original shear strength for collapsed soils with natural water content is relatively large and slope failure doesn't occur because the cohesion in the shear strength is induced by a suction force between the soil particles under unsaturated condition. However, water seepage into the soil induces a drastic decrease in the shear strength, which is mainly caused by a decrease in cohesion (losing suction) resulting from soil saturation. In addition, the drained/undrained condition in the shear process is also sensitive to shear strength. For example, both water seepage and the shear process with constant volume cause an approximate 30z reduction in shear strength for Fukuchi-machi and Sasaguri-machi soil samples. Therefore, the reduction of cohesive strength due to water seepage and the low permeability of the slope are the parameters which trigger geodisaster. Based on the results of slope deformation and a stability analyses which took the change in water pressure and cohesive strength into account, the geodisaster at Fukuchi-machi was simulated, it is reasonable to assume that the shallow failure near the top of slope occurred due to torrential precipitation of about 100 mm per hour which triggered a debris flow.
キーワード: Direct box shear test / Rainfall / Saturated-unsaturated seepage analysis / Slope stability / Stability analysis
URI: http://hdl.handle.net/10069/30993
ISSN: 00380806
DOI: 10.3208/sandf.51.575
権利: © 2011 The Japanese Geotechnical Society
資料タイプ: Journal Article
原稿種類: publisher
出現コレクション:060 学術雑誌論文

引用URI : http://hdl.handle.net/10069/30993

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