| Co-Investigator(Kenkyū-buntansha) |
YAMAGISHI Hiromitsu Faculty of Science, Department of Environmental Science, NIIGATA UNIVERSITY, Professor, 理学部, 教授 (80313500)
WTANABE Naoki Research Institute for Hazards in Snowy Areas, NIIGATA UNIVERSITY, Lecturer, 積雪地域災害研究センター, 講師 (60282977)
SATO Osamu Research Institute for Hazards in Snowy Areas, NIIGATA UNIVERSITY, Professor, 積雪地域災害研究センター, 教授 (00022624)
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| Research Abstract |
Followings are conclusive summary of our investigation.
(1)Many tertiary type landslides are distributed in the Higashikubiki area, Niigata Prefecture. Frequency of landslide occurrences in this area is related to the bedrock geology. Several non-weathered and weathered mudstone samples were collected from landslide areas distributed in Teradomari, Shiiya and Nishiyama geologic formations. Simple and ring shear tests were carried out on these samples. Weathered mudstone samples exhibited higher shear strength than non-weathered mudstone samples. Such phenomenon might depend on the changes of shear resistance of the slip surface of landslides caused by alteration of minerals during chemical weathering.
(2)Triaxial compression test and ring shear test were carried out on clay samples of sliding surfaces in Tertiary type landslides and crystalline schist landslides. Angles of internal friction of residual shear strengths of these samples range from 5 to 30 degree. Their angles of samples fr
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om Tertiary landslides are less approximately 10degree than those of samples from crystalline schist landslides. This fact is concordant with difference of slopes between the two type landslides. Mg content of clay samples is reduced through chemical weathering, ferric and aluminum components are residua relatively increase. Swelling minerals such as chlorite and smectite are closely connected to the lowering shear resistance of clay of sliding surface.
(3)Landslide movements are controlled by bedrock geology and characteristics of soils, and produce unique topographic features. Landslides for once are similar in shape. Creeping landslides, in contrast, are morphologically characterized by aggregates of various partial slumps. Slopes of landslides distributed in Tertiary sediments show less than 30 degree. Slopes of them, in particular, show around 18 degree in mudstone area. Landslides distributed in volcanics show more than 30 degree of slope and their movements are similar to rock slide or rock avalanche.
(4)Slopes of landslides distributed in crystalline schist and in Tertiary sediment range from 15 to 35 degree and from 10 to 20 degree, respectively. Sizes of landslides such as length, width and area in Tertiary sediments are larger than those in crystalline schist. The depth of sliding surfaces of landslides in Tertiary sediments, however, is shallower than those in crystalline schist.
Groundwater tables in landslides in Tertiary sediments are generally shallow and close to surface. On the other hand, many landslides in crystalline schist have deeper groundwater tables than their sliding surfaces. Less
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