Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering)
Online ISSN : 2185-6516
ISSN-L : 2185-6516
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Paper (In Japanese)
  • Yu FUJIWARA, Toshinori SAKAI
    2019 Volume 75 Issue 4 Pages 369-385
    Published: 2019
    Released: October 20, 2019
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     There are various types of instruments to measure the tensile force of ground anchors (hereinafter anchors). In general, the strain-gauge type load meter which substitutes the resistance change of the strain gauge with electric signals to measure the tensile force is used. But affected by thermal expansion and contraction of the strain gauge itself, caused by temperature change, the measurements of the strain-gauge type load meter fluctuate even when external force is not acting on the anchors. The characteristics indicated by the temperature and load meter’s measurements may be used to evaluate the stability of a slope. And the state of the anchor’s tensile force is judged by the changes in the tensile force’s percentage to the designed anchor force. But no definite evaluation method for tensile force that fluctuates continuously due to temperature change has been established. In this paper, we focus on the correlation between the temperature and measured value of the load meter, and evaluate the fluctuations in the tensile force of anchors considering the influence of temperature change.

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  • Ryota TSUDA, Kosaburo HIROSE, Morihisa UEHARA, Hitoshi MATSUBARA
    2019 Volume 75 Issue 4 Pages 386-397
    Published: 2019
    Released: October 20, 2019
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     Shimajiri mudstone distributed in southern part of Okinawa Island is regarded as a good bearing layer because of its characteristics of high N-value. On the other hand, it has been reported that many landslides and slope failures were occurred in the artificial and/or natural slopes founded by Shimajiri mudstone. In addition, many damaged anchors have been observed on the artificial slope founded Shimajiri mudstone, and it has been pointed out that the cause may be related to the physical and chemical weathering of Shimajiri mudstone. Hence, in order to understand the weathering mechanism, it is necessary to study the time-related degradation of Shimajiri mudstone from a perspective of mineral composition, microstructure, and mechanical behavior. In this study, the authors focused on the artificial slope founded Shimajiri mudstone in the southern part of Okinawa Island, and investigated the time-related degradation, the characteristics of its slaking, and the composition of minerals such as clay minerals based on the boring survey in both 1986 and 2016. Then, the physical and chemical weathering mechanism and the weathering progression processes of Shimajiri mudstone were discussed. As a result, it was revealed that the damage of the slope is deeply related to the physical and chemical weathering such as swelling/dissolution of clay minerals and/or oxidation of pyrite.

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  • Akira SHINSEI, Satoshi NISHIMURA, Kazunori FUJISAWA, Yuji TAKESHITA, K ...
    2019 Volume 75 Issue 4 Pages 398-414
    Published: 2019
    Released: October 20, 2019
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     The stability assessment of river levee against intense rainfall and flooding involves predicting variations of the phreatic surface level and pore water pressure through unsaturated seepage analysis. This study is a summary of collective work conducted by JSCE River Levee Research Committee WG2, which was set up in 2012 to investigate the applicability of unsaturated seepage analysis to the levee wetting problems in practice, and to assess the accuracy and robustness of the analysis implemented with different numerical codes by different users. To this end, three levels of round-robin analysis exercise were conducted, in which different degrees of prescription were imposed to analysis conditions. Amongst the main findings from this exercise is that all the numerical codes, whether commercial or home-grown by the authors, output sufficiently accurate and practically identical solutions when same conditions are input, despite the differences in their discretisation methods, integration methods, etc. When the participants were given a total freedom in modelling the given levee’s cross-section and material data, notable variations in the numerical results came out, confirming that each participant’s engineering judgment in conditioning/modelling, not the sensitivity of numerical codes, is the main cause of the diverse outputs. Nevertheless, the variations are on the whole within a range which can be deemed acceptable for most levee engineering purposes.

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  • Yu FUJIWARA, Takashi MITSUZUKA, Hirofumi HISADA, Masaru TAKEMOTO
    2019 Volume 75 Issue 4 Pages 415-429
    Published: 2019
    Released: October 20, 2019
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     When block fields exist on the slope along a road, it is necessary to carry out rockfall surveys and take measures to prevent disasters. But rocks fall because of various, complex causative and triggering factors, and it is difficult to standardize the stability of a block field and evaluate it accordingly. The Rock-fall Vibration Survey method was developed for this reason. The survey is carried out by installing a vibration meter on the block field and using the dominant frequency and subtrahend constant of the recorded vibrations to quantitatively evaluate the stability of the block field. With this method, the vibration meter is installed and removed every time a measurement is taken, and measurements taken for only a short period of time are used to evaluate the stability. But it is possible that block field vibrations change, affected by the environment such as weather conditions. In this study, a facility to monitor the vibrations of unstable block fields is built, and points to keep in mind when evaluating the stability of block fields by analyzing the measured data are indicated.

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  • Hiroaki SANO, Mikio YAMADA, Nozomu KOTAKE, Koichiro OGATA, Hideo KAWAH ...
    2019 Volume 75 Issue 4 Pages 430-442
    Published: 2019
    Released: November 20, 2019
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     In order to utilize reclaimed gypsums derived from waste plasterboards as ground improvement materials, thermal behaviors of reclaimed gypsums and reagent gypsums are investigated in this paper. Furthermore, simple heating method of judging quality of reclaimed gypsums was examined to determine gypsum hemihydrate content.

     As the results, it was found that gypsum dihydrate is changed into gypsum hemihydrate under thermal condition of 90°C and gypsum hemihydrate is changed into anhydrite under that of 120°C with heating of 24 hours. And determining by calculating gypsum hemihydrate content and gypsum dihydrate content with the decrease in mass under the thermal condition of 90°C from 70°C, effectiveness of the estimation of gypsum hemihydrate content by using heating method was shown. Therefore comparing gypsum hemihydrate content determined by both methods of the heating method and the density measuring method, both results were in substantial agreement.

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