| Co-Investigator(Kenkyū-buntansha) |
FUKUOKA Hiroshi Kyoto University, Disaster Prevention, Research Institute, Associate Professor, 防災研究所, 助教授 (40252522)
MARUI Hideaki Niigata University, Research, Institute for Hazards in Snowy Area, Professor, 積雪地域災害研究センター, 教授 (10219545)
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| Research Abstract |
Flow phenomena which brought about most of the casualties in landslide disaster of these years, are caused by liquid-like state of sliding surface and serious reduction of shear resistance. Sassa et al. showed these phenomena are caused by "sliding surface liquefaction" triggered by soil grain crushing in the shear zone and volumetric shrink. This study is focused on the examination of new evaluation method of "sliding surface liquefaction potential" in order to establish methodology of assessment of extension and degree of flow phenomena, with use of geotechnical landslide simulator for earthquake-induced landslides which Sassa developed, based on the parameters of slope angle, geology, geotechnical property, depth of sliding surface, saturation degree, etc.
In the fiscal year 2002 following achievements were obtained
(1) Portable "Grain Crushing Apparatus" which is designed for investigate grain crushing characteristics of soil samples, was improved. Detail microstructure of lens-like
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shear zones of soil samples formed in the, sampel box of the Geotechnical Landslide Simulator for Earthquake-triggered Landslides. Rather interesting fact that the grain crushing much proceeded in the upper and lower boundaries of the shear zone
(2) Shear behaviour characteristics of the soil layer in the vicinity of the potential sliding surface with use of the Geotechnical Landslide Simulator for Earthquake-triggered Landslides by applying three dimensional earthquake acceleration record on the soil samples taken from the Nikawa Landslide site which was triggered by the 1995 Hyogoken-Nambu Earthquake. In the test series, following results were obtained (a) no-sliding surface liquefaction took place in the material that which showed very little displacement although generated excess pore pressure just after the main shock ; (b) rapid-long runout can be triggered in the soil layers that which showed displacement just after mainshock due to excess pore pressure generation, because grain crushing and excess pore pressure generation causes sliding surface liquefaction
(3) A new method was developed to assess excess pore pressure generation during cyclic loading in the soils taken from 1995 Takarazuka-Golf Course Landslide which was triggered by the Hyogoken-Nambu Earthquake, based on volume change due to grain crushing in the drained shear test and one-dimensional coefficient of compressibility. This method shows that drained (not undrained) constant stress test data can assess the excess pore pressure generation in the fully-saturated and undrained condition. Also it implies that the apparatus described in (1) enables sliding surface liquefaction potential measurement even in situ Less
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