Journal of the Japan Society of Engineering Geology
Online ISSN : 1884-0973
Print ISSN : 0286-7737
ISSN-L : 0286-7737
Volume 52, Issue 6
Special Issue
Displaying 1-5 of 5 articles from this issue
Original Article
  • Masahiro YOSHIDA, Masahiro CHIGIRA
    2012 Volume 52 Issue 6 Pages 213-221
    Published: 2012
    Released on J-STAGE: March 31, 2013
    JOURNAL FREE ACCESS
     The collapses occurred in south eastern part of Aomori prefecture caused by The 1968 Tokachi-oki earthquake. This study mention the geological background of the collapses that investigated a stratum of pyroclastic fall deposits, physical property, clay minerals and coefficient of permeability. In south eastern part of Aomori prefecture, pyroclastic fall deposits of from Towada-Hachinohe tephra distributed. A sliding surface of the collapses had been formed at volcanic ash mixed with pumice that below yellowish volcanic ash in pyroclastic fall deposits. Loss of ignition, contents of 10Å halloysite clay minerals increase and NC value by portable penetration test decrease from volcanic ash mixed with pumice. The change of these values contributed to the collapses. Because of volcanic ash mixed with pumice that had low coefficient of permeability distributed in the collapses area.
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  • Masahiro CHIGIRA, Akito NAKASUJI, Shinya FUJIWARA, Masayuki SAKAGAMI
    2012 Volume 52 Issue 6 Pages 222-230
    Published: 2012
    Released on J-STAGE: March 31, 2013
    JOURNAL FREE ACCESS
     The 2011 off the Pacific coast of Tohoku Earthquake induced 4 soilslide-avalanches of pyroclastic fall deposits in Shirakawa city and Nakagawa town, where 6+ and 6− seismic intensities of JMA scale were recorded, respectively. The causal factors of these landslides were slope-parallel bedding of pyroclastics that include very weak paleosol, in which a sliding surface was made, and that beds that slid had been undercut to have lost the support from lower slope. These landslides were highly mobile, which is suggested by apparent friction angles ranging from 10° to 16°. Trees on slopes have been transported on debris in a standing position. Soilslide-avalanches like those described above have been induced by many other earthquakes, which suggests that some pyroclastic fall deposits are very susceptible to earthquake and that we have to identify them to mitigate earthquake induced landslide hazards.
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  • —An Example of a Landslide Located in the Shimanto Belt—
    Yasuhiko WAKIZAKA, Mutsuo KOZUMA, Hiroyuki WATATANI, Yoshiyuki TOYOGUC ...
    2012 Volume 52 Issue 6 Pages 231-247
    Published: 2012
    Released on J-STAGE: March 31, 2013
    JOURNAL FREE ACCESS
     Recently, observation of the detailed constituent geology and geological structure of landslide bodies has become possible by high-quality drilling techniques using surfactants. However, geological information was not obtained from high-quality drilled cores, and it was difficult to distinguish crushed rock due to landsliding and fault breccias. Therefore, detailed geological observations of the fault shear zones and high-quality cores drilled from a landslide body located in the Shimanto Belt, Kyushu, were performed. As a result, some planar fabrics were found in fault breccias around the landslide body, whereas random fabric were found in the breccias of the landslide body; therefore, randomly structured breccias may be an index for geological determining a landslide body. The difference between fault breccias having a planar fabric and a random fabric from the landslide body is attributed to the difference of confining pressure when each breccia was formed. Fault breccias were formed under high confining pressure, Whereas randomly structured breccias of a landslide body were formed under low confining pressure. When geological determining of a landslide body, it is important to classify the degree of crushing, to identify planar fabrics of the rocks and to identify position and frequency of random structured breccias.
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Report
  • Yuri OKAWA, Yuji KANAORI, Teruyoshi IMAOKA
    2012 Volume 52 Issue 6 Pages 248-255
    Published: 2012
    Released on J-STAGE: March 31, 2013
    JOURNAL FREE ACCESS
     Many debris flows were caused in northern Hofu and central Yamaguchi Cities, Yamaguchi Prefecture by a heavy rain, named the “Heavy Rain in Chugoku and Northern Kyushu of July in 2009” after the Japan Meteorological Agency. Late Cretaceous Hofu granitic body is widely distributed in the debris flow area. Fourteen people were killed in Hofu City by the debris flow. Debris flows were occurred also in northern Hofu City by a heavy rain in 1993, and killed four people. In this report, we describe characteristics and distribution of the 2009 debris flow in detail, and then compare the distribution to that of the 1993 debris flow. Source areas of the 2009 debris flow amount to 524, 478 of which occurred in the Hofu granitic region. From rock facies, the granitic body is tentatively classified into coarse-, medium- and fine-grained biotite granites, and granodiorite. Number of the source area per unit area is the most in the coarse-grained biotite granitic region, with the maximum being calculated to be 5.5/km2. The number in the other types of granites is estimated to be less than about one-half of that in the coarse-grained granite. On the other hand, Source areas of the 1993 debris flow amount to 130, 109 of which occurred in the region of medium- and coarse-grained biotite granites. The relationship between the amount of topographic relief of 1 km meshes and the location of the source area indicates that both the 2009 and 1993 debris flows concentrated on the mesh of the elevation interval 201-250 m. Based on the analysis of a summit-level map, the histogram of the 2009 and 1993 debris-flow number have the modes in the elevation interval of 201-250 m and 101-150 m, respectively.
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  • Tomoharu IWASAKI, Norikazu SHIMIZU, Tomohiro MASUNARI, Wataru SATO, Ka ...
    2012 Volume 52 Issue 6 Pages 256-264
    Published: 2012
    Released on J-STAGE: March 31, 2013
    JOURNAL FREE ACCESS
     Monitoring deformations is a key technology for assessing the stability, predicting the risk, managing the safe operation, and reducing the project cost. Although various types of instruments and systems have been developed to achieve successful monitoring, those can be applied to measure one or two dimensional displacements only in local area during short term.
     In order to overcome such limitations, a new type of GPS displacement monitoring system has been developed by the authors. It can continuously monitor the three-dimensional displacements of the ground surface automatically with high accuracy for long term. Besides it provides monitoring results through the internet in real time, and users can see them at anytime and anywhere.
     In this paper, the system is outlined and the practical application results are described.
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