Journal of the Japan Landslide Society
Online ISSN : 1882-0034
Print ISSN : 1348-3986
ISSN-L : 1348-3986
Volume 44 , Issue 6
Showing 1-9 articles out of 9 articles from the selected issue
Original articles
  • Hiroshi NAYA, Masahiro MIZOKAMI, Shinichiro ASARI, Tomohiro MASUNARI, ...
    2008 Volume 44 Issue 6 Pages 339-348
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    A new type of noncontact displacement meter has been developed that employs a diffusion laser beam (DLB) . This DLB system was adopted to reduce the influence of weather conditions on measurements and to avoid any harmful effects to the eyes, skin, etc. To achieve these goals, the DLB displacement meter employs a large-diameter light source and has a large diffusion angle. In addition, it displays the measurement value in real time, performs continuous measurements, can be installed at sites inexpensively, and is capable of measuring displacements greater than 30cm.
    In order to verify the precision, performance, and utility of this DLB displacement meter, some experiments were conducted in the laboratory and outdoors. The results of the laboratory experiments demonstrated that the DLB displacement meter could measure displacements of 10. 0mm on a 50-m baseline length to a precision of within ± 0. 2mm. This precision is higher than that of a surface extensometer, which is a contact-type meter. The open-air experimental results showed that the DLB displacement meter is influenced less by obstacles between the meter and the measurement point than conventional laser-beam displacement meters. In addition, the DLB displacement meter was capable of measuring with a precision of ± 0. 8mm under a visibility of 10m on a 16-m baseline length, whereas a prism total station was not able to measure to the same level of precision under identical conditions. In particular, comparison testing in the open air revealed that the surface extensometer produced appreciable measurement errors due to poor tracking of the invar wire on expansion or contraction, whereas the DLB displacement meter exhibited good tracking of the displacements in front of and behind the reflective plate.
    The DLB displacement meter was applied to landslide monitoring. Its accuracy and applicability were equal to or exceeded those of a surface extensometer in practice.
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  • Yoshitaka KOJIMA, Toshiaki OHKUMA, Masaki KAWASHIMA, Satoru OHTSUKA
    2008 Volume 44 Issue 6 Pages 349-357
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    We have developed a new practical method to obtain both geometric and mechanical information on the ground and the buried structures such as displacement, deformation and load by setting a long-body sensor complex into the ground and measuring its inclination and strain at each point. This method, called the spline measurement method, utilizes the long-body sensor complex and a spline function of B-spline basis. We have conducted not only numerical simulations, but also bending experiments of long-bodies at both laboratory and in-situ site using actual pipes. Measurement of active landslide was also carried out. The applicability of proposed method was widely examined in addition to referring to the principle and theory of spline measurement. Discussions were made on adopting conditions, accuracy and further problems of proposed method.
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  • Takashi OKAMOTO, Sumio MATSUURA, Shiho ASANO
    2008 Volume 44 Issue 6 Pages 358-368
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    This paper clarified the deformation mechanism of a shallow landslide in a Tertiary deposit with 3 to 5 meters of maximum snow depth based on the results of two years of monitoring. Landslide activity was low from spring to summer; however, it increased from autumn to the early snow season, and the extensional deformation increased with it. The creep of the landslide, which stopped briefly in midwinter, started moving at a slow speed without deformation in the snowmelt season. The following three factors were apparently involved in controlling such deformation: 1) increase in shear strength by snow load, 2) net effect of snow pack, and 3) consolidation of the sliding surface by long-term loading of snow pack.
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Research notes
  • Hiroshi MORIYA, Akihisa TAKAHASHI, Shinro ABE, Daisuke HIGAKI
    2008 Volume 44 Issue 6 Pages 369-376
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    The objective of this research was to clarify the three-dimensional deformation structure of the moving body of landslides. The analysis was based on landslides in the Tohoku district and existing observation data, and revealed that deformation of the moving body has two types. In one type, the displacement of the slip surface is almost equal to the displacement of the ground surface. In the other type, the rate of displacement is fast in the central parts, slow at the ends of the horizontal sides, and along the vertical sides it increases gradually from the slip surface towards the ground surface. Furthermore, the displacement was found to be like a viscous flow similar to debris flows or plastic deformation seen in glaciers. These types of deformation depended on the position within the landslide body as well as constituent materials. It is therefore presumed that such types of deformation are related to the extent of fracturing or weathering of moving body components. The results of this study will be useful for designing restraint works based on analyses of the three-dimensional stability and deformation of landslide slopes.
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  • Mitsuo NAKAGAWA, Masao YAMADA
    2008 Volume 44 Issue 6 Pages 377-384
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    Landslide movement is a phenomenon that a relative shear movement on the slip surface between moving layer and immobile layer continues. It is effective to apply a particular numerical analysis method that the reproduction of continuous relative displacement (large displacement) on the slip surface can be simulated stably. In this study, we examined the applicability of the finite difference method formulated by the explicit dynamic formulation to the landslide movement analysis. This numerical analysis method is applied when slope collapse or reactivated landslide is induced. This method allowed us to reproduce characteristic phenomenon respectively observed in such slope disaster.
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  • Kei HIGUCHI, Kazunori FUJISAWA, Masaru TOUHEI, Shigeru OKAWA, Hiroyuki ...
    2008 Volume 44 Issue 6 Pages 385-392
    Published: March 25, 2008
    Released: December 26, 2008
    JOURNALS FREE ACCESS
    Sediment deposited at the foot of landslides stabilizes them temporarily, but removal of such sediment when installing emergency measures requires extra caution to avoid reactivating the landslide. It is therefore necessary to remotely monitor the movement of landslides to avoid secondary disasters for safety reasons as well as for reliable monitoring.
    One of the main remote monitoring methods is to use a non-prism type optical total-station, which is useful for measuring the ground displacement from observation stations because no measurement target is needed. However, the measurement error may be higher than that of an optical total-station that uses targets, and measurement at night is extremely difficult. To overcome these problems, in this study we developed a new method of remotely setting up targets for an optical total-station from landslides. This new method uses a crossbow and a paint capsule attached at tip of arrow. A paint capsule is launched by crossbow, broken and gets on slope as a target of total-station with ± 300cm of accuracy at 300m distance. The target helps the displacement monitoring in landslide.
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