Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering)
Online ISSN : 2185-6516
ISSN-L : 2185-6516
Volume 76 , Issue 2
Showing 1-8 articles out of 8 articles from the selected issue
Paper (In Japanese)
  • Naoki SHIMURA, Motoyuki SUZUKI, Hiroki UCHIKAWA
    2020 Volume 76 Issue 2 Pages 110-121
    Published: 2020
    Released: April 20, 2020
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     To investigate the residual pullout resistance characteristics of the reinforcement in a reinforced earth wall, we examined the pullout behavior of reinforcement up to a certain initial displacement. First, the displacement-controlled pullout test was conducted on the test apparatus that reproduced stress conditions around the reinforcement, and the basic pullout resistance characteristics of the reinforcement were determined. Second, a load-controlled pullout test was performed. In this test, after applying an initial displacement, the load-controlled condition was applied, and the pullout load was maintained. From the pullout behavior of the reinforcement, we clarified the influence of initial displacement and pulling of the load on residual displacement and cumulative displacement. Furthermore, we evaluated the residual resistance of the reinforcement. Thus, we clarified that if the pullout load is constant, the subsequent pullout displacement increases with the initial displacement of the reinforcement. In a nutshell, if the displacement does not exceed the inflection point of the pullout curve, the residual resistance of the reinforcement is sufficient.

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  • Hiroyasu OHTSU, Takafumi KITAOKA, Takaaki BABA, Mitsuru YABE, Ken SAKU ...
    2020 Volume 76 Issue 2 Pages 122-141
    Published: 2020
    Released: April 20, 2020
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     In this study, based on the in-situ measurement results on the fill slope where macro-pores were developed, the influence of preferential flow due to heterogeneous pore distribution on rainfall infiltration and drainage characteristics was discussed. As a result, the following possibilities are shown.

     First, in the slope where macro-pores have been developed, when pore-water pressure and volumetric water content increase rapidly due to rainfall, a preferential flow occurs as the permeability of soil containing macro-pores increases by several orders. And since the preferential flow forms a pseudo-saturated region in a short time, the pore-water pressure increased almost coincident with the rainfall peak due to the subsequent high-intensity rainfall. Accordingly, it is considered that since this pore-water pressure transmission occurs in a short time, the occurrence time of the shallow slope failure may be much faster than the result estimated by the conventional seepage flow analysis same as the past slope failure incidents.

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  • Yu OTAKE, Kyohei SHIGENO, Shinya WATANABE, Yosuke HIGO, Shogo MURAMATS ...
    2020 Volume 76 Issue 2 Pages 142-157
    Published: 2020
    Released: April 20, 2020
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     Recently, the need for the robust design and the resilience design methods under accidental loading of soil structures has been the subject of many discussions. Herein, we are developing a dynamic reliability analysis base on mode decomposition for evaluating the failure mode of the soil structure. This analysis features quantifying uncertainties related to the accuracy of the parameter settings. This paper describes the deformation calculation procedure for the case of a simple embankment on a liquefiable sand layer. We conducted a dynamic effective stress analysis to evaluate the liquefaction phenomenon in the sand layer. This study aimed to derive an alternative numerical analysis model that considers the space and time required for calculating the aforementioned deformed embankment.

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  • Michitaka OKAMOTO, Yukiyoshi KITAMOTO, Teru YOSHIDA, Shintaro OHNO, Ak ...
    2020 Volume 76 Issue 2 Pages 158-173
    Published: 2020
    Released: April 20, 2020
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     The surface soil stabilization with laying planer geosynthetics such as geogrids, geotextiles, has been applied to many construction works on soft ground. The authors have newly developed a reinforcement material for this soil stabilization, called “the Lattice-Frame-Reinforced (LFR) sheet”. The LFR sheet combines a geotextile and a lattice frame which is composed of “geojacket” formed by filling a mortar into fabric hose called “jacket”. The lattice-frame of geojacket can reduce the risk of tensile failure of the geotextile sheet due to excessive local load which is a problem of the surface soil stabilization with conventional geosynthetics, since the geojacket can support a certain amount of bending stress. Furthermore, a soil layer reinforced by the LFR sheet can provide larger bearing capacity compared with using conventional geosynthetics, because the lattice frame confines the shear deformation of the inside soil. In this paper, the characteristics and application of surface soil stabilization with the LFR sheet are described.

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  • Shinichiro SHIRAGA, Genki HASEGAWA, Yasuo SAWAMURA, Makoto KIMURA
    2020 Volume 76 Issue 2 Pages 174-190
    Published: 2020
    Released: May 20, 2020
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     Vacuum consolidation methods allow a soft ground to be consolidated without the shear deformation of the ground. That is, the safe construction of an embankment can be achieved by combining a vacuum consolidation method and embankment loading. The stabilizing effect of vacuum consolidation methods has been verified through many construction examples, and it has been reported that measuring or predicting the pore pressure through on-site numerical analyses and experiments is important to evaluating the stabilization of the ground. In this study, centrifuge model experiments and numerical analyses focusing on the mechanical behavior around the drain in a soft ground were conducted to investigate the effect of both the period preceding vacuum consolidation before the embankment construction and the embankment speed on the pore water pressure. As a result, the relationship between the preliminary period of vacuum consolidation and the embankment speed, which can suppress the increase in pore water pressure due to embankment loading and has a stabilizing effect on the ground, was clarified. Furthermore, the local consolidation behavior around the drain was clarified.

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  • Takuya EGAWA, Koichi ISOBE, Osamu HATAKEYAMA
    2020 Volume 76 Issue 2 Pages 191-203
    Published: 2020
    Released: May 20, 2020
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     In this study, the decrease in the horizontal subgrade reaction coefficient of piles in liquefied volcanic ash ground was quantitatively evaluated by using a centrifugal model test with a liquefaction strength ratio of ground as a parameter. A relational equation which describes the decrease in the horizontal subgrade reaction coefficient of piles in liquefied ground was proposed and the related coefficients were evaluated. As a result, it was confirmed that the coefficient which presents the decrease level was correlated with the liquefaction strength ratio of ground, and the coefficient for volcanic ash ground was evaluated nearly twice as large as that for sandy ground. The above examination revealed that it would be generally sufficient to regard the decrease in the horizontal subgrade reaction coefficient of piles in liquefied volcanic ash ground as being about half that in sandy ground.

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  • Hideyuki SAKURAI, Toshiko YAMADA
    2020 Volume 76 Issue 2 Pages 204-214
    Published: 2020
    Released: May 20, 2020
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     A new point-source (PS) model is proposed for the finite element analyses (FEAs) of groundwater seepage flow. In FEAs, the effects of borehole pumping or injection are often approximated by nodal PSs because the boreholes are small in comparison to the analysis areas. To obtain accurate results, the elements that are connected to the PS (ECPSs) must be of a certain size corresponding to the borehole radius. This considerably restricts unfettered mesh generation. The proposed PS model facilitates the use of arbitrary unstructured meshes by correcting the permeability of the ECPSs based on theoretical solutions. In addition, the proposed model allows the analysis to be performed using existing analysis codes without any changes because the proposed model can be used to carry out the pre/post-processing step to revise and restore the ECPS permeabilities. The efficacy of the proposed model is verified by using it to solve two simple problems. Structured and unstructured meshes based on three types of elements are prepared for each of the two problems. The verifications using the proposed model provide accurate results.

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Technical Note (In Japanese)
  • Kaoru KOBAYASHI, Kazunobu MATSUMOTO, Asuka SUZUKI, Toshihiro MORII
    2020 Volume 76 Issue 2 Pages 215-220
    Published: 2020
    Released: May 20, 2020
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     Capillary barrier (CB) is a tilting soil layer system which is composed of a fine soil layer overlaid on a coarse soil layer. Suitable materials for the fine soil and coarse soil used to make a CB are not confirmed. In particular, it is important to clarify that the fine soil has sufficient influence on the diversion length of the CB system. A horizontal distance from the beginning of water flow to this point of percolation is called a diversion length of the CB, and is one of important parameters in designing structural dimensions and configuration of the CB system. In this paper, the theoretical equation proposed by Ross-Steenhuis, fine soil permeability, water retention, are used to clarify an appropriate a fine soil for maximizing diversion length.

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