Journal of the Japan Society of Erosion Control Engineering
Online ISSN : 2187-4654
Print ISSN : 0286-8385
ISSN-L : 0286-8385
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Volume 67, Issue 1
Displaying 1-13 of 13 articles from this issue
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Technical Papers
  • Improved reinforcement by rockfill materials in small wooden check dams
    Quoc Dung DANG, Yoshiharu ISHIKAWA, Taeko WAKAHARA
    2014 Volume 67 Issue 1 Pages 3-10
    Published: May 15, 2014
    Released on J-STAGE: December 01, 2016
    DOIhttps://doi.org/10.11475/sabo.67.1_3
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    Shear deformation of small wooden check dams under the actions of earth pressure is an important factor in dam stability. In this research, experiments were conducted on dam models. Changes in shear behaviors and shear resistance forces from installing a wooden pile into rockfill materials (average diameter 69 mm) were investigated. Moreover, to check the applicability of Kitajima's equation and Itoh's equation for evaluating shear deformation, large scale direct shear tests (0.54 m3) were carried out to examine the internal friction angle of rockfill materials. The results showed that the shear resistance force was remarkably increased when a wooden pile was installed with an attached protuberance at an angle of 30° against the shear plane of rockfill materials. The internal friction angle over a large range of stresses was 44°. Thus, Kitajima's equation is not suitable for evaluating shear deformation in a wooden check dam. Itoh's equation gives an estimation of the deformation ratio γ =0.0755 that is 30% lower than the actual. On the basis of these results and testing, this economical reinforcement method, which has a strong reinforcement effect, is recommended.
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  • Countermeasures against a landslide dam in Nagatono caused by Typhoon 12 in September 2011 －Countermeasures against a large landslide dam with a high head and steep slope
    Wataru SAKURAI, Ryo SAKAI, Makoto OYAMA, Takahisa MIZUYAMA, Akihiko IK ...
    2014 Volume 67 Issue 1 Pages 11-18
    Published: May 15, 2014
    Released on J-STAGE: December 01, 2016
    DOIhttps://doi.org/10.11475/sabo.67.1_11
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    An overflow channel and a sabo dam, which dissipates energy in the water flowing through the overflow channel and prevents foot scouring of the landslide dam, are currently being designed as countermeasures against the Nagatono landslide dam. However, the head of the overflow channel is as high as 80 m. Additionally, the dam has a steep slope of 1/2.5, and the dam's slope is curved. Because these conditions make it difficult to predict hydraulic phenomena, designing appropriate countermeasures is problematic. Therefore, we conducted hydraulic experiments to assess the efficacy of the proposed design and to confirm the effects of the overflow channel and the sabo dam. During experiments, a shock wave appeared on the slope and the curved section of the overflow channel due to the water's high velocity and drift current, but the water flow was controlled to safe levels using a raised revetment, the height of which was determined using the Nappe equation. When the length of the energy dissipater was determined based on the technical standard, more frequent overflow was observed on the wing of the sabo dam due to whirlpools caused by the drift current. Therefore, we concluded that, under these conditions, the energy dissipater needs to be longer. These results demonstrate the necessity for conducting hydraulic experiments during the planning and design stages to ensure the location and height of sabo dams are appropriate to ensure adequate reductions in water energy.
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  • Application of the pipe jacking method as a means of drainage from landslide dam
    Wataru SAKURAI , Ryo SAKAI , Yasuyuki OOTUKA , Hiroaki AOKI , Hide ...
    2014 Volume 67 Issue 1 Pages 19-27
    Published: May 15, 2014
    Released on J-STAGE: December 01, 2016
    DOIhttps://doi.org/10.11475/sabo.67.1_19
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    When it was hit by Typhoon No. 12 in September 2011, a huge landslide dam was formed in the riverbed in Kuridaira district of Totsukawa Village in Nara prefecture, Japan. In October 2011, emergency counter measures were initiated, and an overflow channel that was used for the temporary drainage of the dam pool was constructed. However, during Typhoon No. 17 in September 2012, the flood waters eroded the channel and broke approximately two-thirds of the length of its banks. Fixing or reconstructing the drainage became urgent, so the drainage would last until the next flood season. A section of underground drainage pipes located 10-meters beneath the broken channel was used. There are two different methods of pipe construction : the pipe jacking and the cut and cover method. Due to the building period and to promote economic efficiency, the pipe jacking method was adopted. Despite possible construction challenges, such as vulnerable ground conditions and disturbance from tree trunks buried in the collapsed soil, a section of pipe 160 meters in length was installed within a one-month period, which was half the time the original estimate stated it would take. The construction process presented here was recognized as an efficient way to drain landslide dams.
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Research Notes
  • Numerical simulation for deformation of landslide dam by overtopping water
    Fumiaki AKAZAWA, Yoshifumi SATOFUKA
    2014 Volume 67 Issue 1 Pages 28-34
    Published: May 15, 2014
    Released on J-STAGE: December 01, 2016
    DOIhttps://doi.org/10.11475/sabo.67.1_28
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    Heavy rainfall and strong earthquakes cause large-scale landslides and create large landslide dams in mountain rivers. When it retains a large amount of water and bursts, it may cause inundation and catastrophic damages in the downstream area. Therefore, the study of landslide dam deformations is essential for predicting flood potential and flood risk. To predict the flood risk of a landslide dam, we developed a numerical model to simulate the landslide dam erosion by overtopping. The model calculates the process of overtopping erosion in two-dimensions. To improve the prediction of the outflow discharge, we incorporated the inertial debris flow model proposed by Takahashi et al. (2002), the side bank erosion model, and the slope collapse model. We verified the model results by comparing them with the experimental results of Takahashi et al. (1993). The comparison showed that the model is capable to predict the outflow discharge of a landslide dam collapse by overtopping. In addition, we examined the effects of side bank erosion on the dam erosion process, and showed that the side bank erosion affects the overtopping erosion and outflow discharge.
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  • Administrative background of the term “Sabo”
    Akiyasu KURISHIMA
    2014 Volume 67 Issue 1 Pages 35-40
    Published: May 15, 2014
    Released on J-STAGE: December 01, 2016
    DOIhttps://doi.org/10.11475/sabo.67.1_35
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    A Japanese term “Sabo”, which dates back to early 1870 s and would literally mean “sand prevention”, denotes the policies to control erosion and torrents in upstream areas. This study traces the historical background of the term “Sabo” in an administrative context, drawing upon public archives. Those policies were first called “Bosha” when they were introduced in 1873. The word “Bosha” stands for the two same characters, but in reverse order, which constitute the term “Sabo”. Soon afterwards those two terms had been used concurrently and often confounded for more than a decade. Since the institution of the Sabo Act in 1897, however, the term “Sabo” has been established as a legal concept which encompasses both public works and regulatory measures designed for erosion and torrent control.
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