Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering)
Online ISSN : 2185-6516
ISSN-L : 2185-6516
Volume 77, Issue 2
Displaying 1-7 of 7 articles from this issue
Paper (In Japanese)
  • Takumi SHIRAKAWABE, Hailong WANG, Shigeru GOTO, Shuichi YAMAMOTO, Hide ...
    2021 Volume 77 Issue 2 Pages 103-117
    Published: 2021
    Released on J-STAGE: April 20, 2021
    JOURNAL FREE ACCESS

     Bentonite buffer in disposal project for high-level radioactive waste is expected to delay migration of radioactive nuclides, because it has low water permeability and can fill up the technical gaps between overpack and bedrock by swelling during saturation. However, high-level radioactive waste generates decay heat and it is concerned that bentonite buffer may experience functional decline in terms of swelling property and low water permeability because of the thermal history of the buffer. To address this problem, this study measured swelling pressure and water absorption of bentonite that experienced thermal history. The following conclusions are obtained based on this study: i) Effect of thermal history on swelling pressure may not be significant. ii) Diffusivity and water absorption rate of compacted bentonite specimen with dry density less than 1.6 Mg/m3 may increase for cases when temperature equals or higher than 160℃ and thermal history equals or longer than 30 days. iii) It is expected that thermal history effect on water movement in buffer would be minor for properly designed maximum temperature in disposal site and dry density of the buffer.

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  • Shintaro MIYAMOTO, Yoshihisa MIYATA
    2021 Volume 77 Issue 2 Pages 118-128
    Published: 2021
    Released on J-STAGE: April 20, 2021
    JOURNAL FREE ACCESS

     Advanced soil reinforcement should be useful to carry out road restoration following a disaster. A deployable geocell reinforcement inspired by the self-deployable structure in space and mechanical engineering was designed for the road restoration. The deployment conditions and reinforcement shape were simulated. A series of laboratory tests were conducted to investigate the reinforcing effect, and it was confirmed that the soil-geocell interface shear resistance increases as the cell reinforcement confines the soil dilatancy. Based on the Taylor-Bishop energy correction formula, an empirical formula is proposed for the soil-geocell interface shear resistance.

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  • Keigo KOIZUMI, Mitsuru KOMATSU, Kazuhiro ODA, Shinichi ITO, Hiroshi TS ...
    2021 Volume 77 Issue 2 Pages 129-139
    Published: 2021
    Released on J-STAGE: May 20, 2021
    JOURNAL FREE ACCESS

     Rainfall-induced shallow landslides have become more frequent owing to recent occurrences of extreme weather in Japan. The authors obtained research finding from previous studies that slope deformation due to rainfall-induced shallow landslide starts to increase after reaching the initial quasi-saturated volumetric water content (IQS). On the other hand, it was pointed out as problems to confirm the behavior of volumetric water content in the depth direction with respect to slope deformation and verify the consistency between the model test result and the filed measurement result. In this research, we summarized the results of a model experiment and a field measurement to solve these problems. By grasping the temporal change of volumetric water content in the depth direction, it is possible to understand the process from detection of IQS to formation of saturated zone, rise of water level and occurrence of displacement. When the measurement result on the actual slope were considered based on the result of the model slope experiment, it was confirmed that the result on the actual slope agree well with the result of the model slope experiment. In addition, when the IQS index was created as an index for judging whether the slope reached the IQS during rainfall and applied to the measured data on the actual slope, it was shown that the time when the volumetric water content reached IQS could be detected in real time.

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  • Nobutaka HIRAOKA, Naotaka KIKKAWA, Kazuya ITOH
    2021 Volume 77 Issue 2 Pages 140-158
    Published: 2021
    Released on J-STAGE: May 20, 2021
    JOURNAL FREE ACCESS

     In order to prevent occupational accidents caused by landslide, the design of the structure must be based on the ground conditions. However, there are cases where the design cross-section is determined based on various guidelines, laws and regulations, and design guidelines, etc. without ground investigation. When considering the stability of a slope, it is necessary to determine the design cross-section considering the influence of water such as groundwater and springs as well as the excavation geometry. In this paper, centrifuge model experiments were carried out to simulate the slope shape specified in the Road Earth Construction Guideline and Ordinance on Industrial Safety and the Occupational Safety and Health Regulations Article No. 356, and to verify how the slope would fail due to groundwater rise. As a result, it was confirmed that the slope would be stable if there was no influence of the groundwater in the prescribed shape, but it was confirmed that the slope would collapse when the groundwater rises. In addition, a countermeasure for the drainage of groundwater by drainage pipes was investigated. The stability of the slope was improved by the drainage pipes installed only at the bottom of the slope.

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  • Yukihiro MORIKAWA, Ryo YOSHIDA, Chiaki YOSHIZAWA, Kenich MAEDA, Tatsuy ...
    2021 Volume 77 Issue 2 Pages 159-171
    Published: 2021
    Released on J-STAGE: May 20, 2021
    JOURNAL FREE ACCESS

     In this study, converter slag, which has problems with expandability and pretreatment to prevent it, was studied. The advantages of converter slag as a ground improvement material were studied, focusing on its frictional properties, grain size characteristics, and hydraulic properties. The present study showed that mixing fine grained soil with gravel and sand-rich converter slag improved the particle size distribution of the soil mixture. As a result, the compaction characteristics of the mixtures were greatly improved and the lack of compaction was less likely to occur regardless of the compaction method. It was also found that the ground strength of the soil mixture increased with the mixing rate of the converter slag, and that the fine-grained soil acted as a cushion to reduce the expansion of the converter slag. Furthermore, the effect of mixing slag into the soil was found to increase the improvement of the cement by improving the particle size distribution, alkalization, and decreasing the unit water volume for mixing of target soil.

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  • Yoshihiko HIBI
    2021 Volume 77 Issue 2 Pages 185-194
    Published: 2021
    Released on J-STAGE: June 20, 2021
    JOURNAL RESTRICTED ACCESS

     Pressure equations and hybrid equations could been derived from Richards equation and have been frequently employed for investigation and study of seepage flow and multiphase flow. Variables of pressure equations and hybrid equations are gas and water pressures and water pressure and water saturation, respectively. On the other hand, saturation equations in which a variable is only water saturation had been rarely used in the investigation and study. However Klute saturation equation and Peaceman saturation equation are explained in some books and articles. This paper organized the derivation of the Klute saturation equation and Peaceman saturation equation and compared the two saturation equations. Furthermore in this paper distributions of water saturation obtained by numerical simulations with Klute saturation equation and Peaceman saturation equation were compared with that calculated from capillary pressure which equals difference between hydrostatic pressure and static gas pressure. As a result, the distribution of water saturation obtained by Peaceman differed from that obtained from Klute saturation equation and was more accurate than Klute saturation equation.

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Technical Report (In Japanese)
  • Hiroaki SANO, Hidekazu MORIOKA, Hiroshi KAWAMITSU, Mikio YAMADA, Nozom ...
    2021 Volume 77 Issue 2 Pages 172-184
    Published: 2021
    Released on J-STAGE: May 20, 2021
    JOURNAL FREE ACCESS

     In this study, in order to investigate the application of the new water content measuring method of reclaimed gypsums derived from waste plasterboards by using unheated type, we performed the basic tests on measuring water content by using “glycerol-method”.

     As the results, it was found that the refractive index varied depending on elapsed time after dripping glycerol on prism, the influence of the refractive index on water mixing time was not recognized. And in the case directly dripping the sample solution on prism by using syringe for reagent gypsum dihydrate, the water content measuring glycerol method was close to true water content and liner relation with high correlation was obtained, the validity of water content measuring by using unheated type was confirmed.

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