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)
  • Tomonari MAEDA, Yoichi SHIMADA, Shinichi TAKAHASHI, Shigehiko SUGIE, J ...
    2021 Volume 77 Issue 1 Pages 1-17
    Published: 2021
    Released: January 20, 2021

     Inclined braceless excavations are characterized by lower earth pressure acting on the wall compared to vertical walls, allowing for reduced wall rigidity and omission of shoring. The authors have previously evaluated the retaining wall deformation and stability of inclined braceless retaining walls up to 10m deep through centrifugal model experiments at a centrifugal model experiments at a centrifugal acceleration of 50g using varied foundation materials. The model experiments quantitatively confirmed that the deformation arising from excavation can be reduced by inclining the retaining walls.

     The authors developed a design method for inclined braceless excavation support using elasto-plastic beam spring analysis, modeling the retaining wall as an elastic beam of finite length and the foundation as an elasto-plastic spring, and applied the design method to actual construction sites.

     This paper reports on the validity of the proposed design method by comparison of centrifugal model experimental results with analytical results using the proposed design method and inverse analysis of actual cases performance where the design methods were implemented at construction sites.

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  • Erika SHIOTA, Ryo TAKENAKA, Toshifumi MUKUNOKI
    2021 Volume 77 Issue 1 Pages 18-31
    Published: 2021
    Released: January 20, 2021

     It is difficult to evaluate how extention and cleaning soil can be contaminated by light-non-aqueous phase liquid (LNAPL) because LNAPL behavior in porous media is dependent on multiphase flow in pore structure which is composed of complex parameters (e.g. pore scale, connectivity, and tortuosity).

     The objective of this study is to investigate water-LNAPL fluid dynamics in porous media under different temperature conditions. In this paper, a temperature controllable injection device for a micro focused X-ray Computed Tomography (µ-XCT) scanner was used to conduct different temperature injection experiments. In addition, the pore-scale distribution and structure as well as the focused interfacial phenomena of water-LNAPL were evaluated and observed image analysis. From the experimental results and image analyses, it was found that water-LNAPL fluid dynamics are variable under different temperatures and dependent on interfacial tension and viscosity, which that is a factor sensitive to temperature changes.

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  • Satoshi NONAMI, Satoru SHIBUYA, Satsuki KATAOKA, Nobuyuki TORII, Katsu ...
    2021 Volume 77 Issue 1 Pages 32-42
    Published: 2021
    Released: January 20, 2021

     In this paper, a method for estimating the degree of compaction of in-service embankment by having the result of dynamic cone penetration (DCP) test. Based on the results of laboratory DCP test performed using a chamber comprising the compacted soil to different degrees, an empirical equation for estimating the degree of compaction by using the number of blows from the DCP test, Nd-value, the particle size at 80 percent passed, D80, and the fines content, Fc is proposed. The applicability of the proposed equation was fairly well validated by showing that the estimated degree of compaction was close to the measured value. The degree of compaction for an embankment exhibiting variations of the Nd-value as well as the grain size distribution was similar when compacted under similar conditions. In this case study, the importance of estimating the degree of compaction, which in turn enables using to estimate the angle of shearing resistance was successfully demonstrated. By considering the fact that the Nd-value decreases as the water content increases, it is described that the proposed equation provides safer side of the estimate applicable to embankments having the water content higher than the optimum value.

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  • Hiroki SAKAMOTO, Fumio TATSUOKA, Hideki SODA, Hiroaki KOBAYASHI, Takas ...
    2021 Volume 77 Issue 1 Pages 43-58
    Published: 2021
    Released: January 20, 2021

     To properly construct impermeable embankment, typically the core zone of rock-fill dam, it is required to ensure a sufficiently low hydraulic conductivity, in addition to sufficiently high strength. To this end, the grading characteristic and moisture content, w, of fill material are controlled and the w value and dry density of compacted soil are measured and controlled. Conventionally, the compaction is controlled by lower limit management of the degree of compaction, Dc, and upper and lower limit management of w. In this method, however, it is difficult to efficiently exclude poor-quality compaction while facilitating high-quality compaction. To solve these problems for the construction of a 139 m-high Koishiwaragawa dam, a series of laboratory and test filling was performed at various compaction energy levels, soil types, and w values. It was confirmed that the compaction becomes more efficient by implementing a relevant lower bound control of the saturation degree, Sr, together with the control of w and Dc specified based on the Sr control. The quality control record during the dam construction showed that the new method could achieve sufficiently high quality of embankment, even higher than a number of previous similar rock-fill dams.

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  • Mitsuo MOURI
    2021 Volume 77 Issue 1 Pages 59-69
    Published: 2021
    Released: February 20, 2021

     This paper has tried to improve the understanding of a main cause for the difference of the particle-size distribution between the Sieve-Hydrometer Method (SHM) and the Laser Diffraction Method (LDM). The basis for this study is a series of particle-size analyses using 8 fine-textured soil samples applying the two methods. Photographs of fine-grained soils were taken by a Scanning Electron Microscope (SEM) at a magnification of 2,000 examining in detail the particulate shapes. A model calculation was executed using Heywood’s approximate method for obtaining terminal falling velocities of non-spherical particles. The above experimental values were compared with these calculation values, and the influence of the irregularity of particle shapes on settling velocity reduction was examined in detail based on the result.

     As a result of this study, the following observations and considerations were made: 1) the particle-size analysis demonstrated that the SHM overestimated the percentages of fine-grained fraction (<10μm) with respect to the LDM; 2) the SEM photographs indicated that most of fine-grained soils were irregular in shape, or were platy, tubular, flat disc-like, and rod-like in shape; 3) in fine-grained fraction, SHM diameters tended to be considerably smaller than LDM diameters at the same cumulative percentage of the particle-size distribution; and 4) non-spherical particles in hydrometer measurements had longer settling time than their equivalent spheres, which resulted in an overestimation of the fine-grained fraction. There is a high probability that a critical factor differentiating the two methods is that the particle shapes in fine-grained fraction differ significantly from spherical forms.

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