Papers - KYOKOWA Hiroyuki
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Fundamental investigations of oxidation method of mud-rock containing pyrite Reviewed
2024.08
Language：Japanese Publishing type：Research paper (conference, symposium, etc.)
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Liquefaction behaviour of aluminium and plastic rod assemblies using bi-axial apparatus with application of image analysis Reviewed International coauthorship
Rawiwan Sukhumkitcharoen, Junichi Koseki, Hiroyuki Kyokawa, Masahide Otsubo
E3S Web of Conferences 544 10002 - 10002 2024.07
Language：English Publishing type：Research paper (international conference proceedings) Publisher：EDP Sciences
It has recently been shown that the overall deformation characteristics of granular materials during liquefaction seems to be governed by local void ratio characteristics. The aim of this study is to investigate the relationship between mechanical properties and local void ratio changes during liquefaction in two materials of different weights (aluminium-type and plastic-type rod assemblies). A series of constant-volume cyclic bi-axial loading tests was conducted together with the image analysis obtaining local void behaviour. The experimental results demonstrate that the first liquefaction resistance of the plastic sample is higher than the aluminium one, corresponding to its smaller initial void ratio and less contractive behaviour observed in the early stage of drained monotonic compression. However, after experiencing the first liquefaction and subsequent re-consolidation histories, a liquefiable assembly of aluminium and plastic rods both became either denser (densification) or more homogenous (homogenization) in terms of local void ratio, suggesting an increase in liquefaction resistance in the next liquefaction stage. This work also includes a preliminary analogous study using a semi-3D discrete element method (DEM) with one single layer of spherical particles to simulate the similar liquefaction behaviour observed in the laboratory tests.
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地山の堆積構造に着目したトンネルの時間遅れ変状メカニズムに関する検討 Reviewed International coauthorship
劉長建，崔瑛，京川裕之，菊本統，池田慧生
岩盤力学に関するシンポジウム講演集 50 ( 1 ) 2024.01
Language：Japanese Publishing type：Research paper (conference, symposium, etc.)
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Water and soil particle movement in unsaturated bentonite with constrained and free swelling boundaries Reviewed
Hailong Wang, Yuka Yamamoto, Hiroyuki Kyokawa, Daichi Ito, Hideo Komine
Soils and Foundations 63 ( 4 ) 101350 - 101350 2023.08
Publishing type：Research paper (scientific journal) Publisher：Elsevier BV
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Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay Reviewed
Misa Hiraga, Hiroyuki Kyokawa, Junichi Koseki
Canadian Geotechnical Journal 2023.05
Language：English Publishing type：Research paper (scientific journal) Publisher：CANADIAN SCIENCE PUBLISHING
A series of one-dimensional cation infiltration tests under different drainage/infiltration conditions, infiltration times, ion concentrations (Na+), and vertical stresses were performed to comprehensively understand the osmotic consolidation of bentonite. The local behaviour of the specimen was captured on a digital camera through a transparent acrylic oedometer ring by tracking the movements of the marker sands on the side of the specimen. The Na+ concentration of the pore fluid throughout the specimen was measured after the test to investigate the spatiotemporal relationships between consolidation behaviour and cation infiltration. In the initial period of infiltration, the pore water pressure measured at the undrained bottom increased. A local swelling behaviour inside the specimen was observed during osmotic consolidation. The low permeability of expansive soils obstructs osmotically induced water drainage from the interlayer space of the expansive clay mineral, especially in regions far from the drainage boundary. This transition of pore water pressure affects the local mechanical behaviour; the dissipation of pore water pressure is followed by settlement. Therefore, the process of osmotic consolidation is totally longer than that of pure mechanical consolidation.
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Liquefaction characteristics in triaxial tests under various gravity environments – DEM analyses Reviewed
Masahide Otsubo, Sanjei Chitravel, Reiko Kuwano, Hiroyuki Kyokawa, Junichi Koseki
Computers and Geotechnics 156 105245 - 105245 2023.04
Publishing type：Research paper (scientific journal) Publisher：Elsevier BV
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A new index for the strength analysis and prediction of cement-mixed soils Reviewed
Tuan A. Pham, Hiroyuki Kyokawa, Junichi Koseki, Daniel Dias
EUROPEAN JOURNAL OF ENVIRONMENTAL AND CIVIL ENGINEERING 27 ( 4 ) 1512 - 1534 2023.03
Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD
In geotechnical projects involving soft soils, cement-mixed soils are an excellent way to improve the mechanical behaviour and engineering performance of soils. The water-to-cement ratio, cement content, and porosity are the most critical parameters impacting the strength of cement-mixed soils, but their effects are less well understood. The proportional influence of cement amount, porosity, and moisture content on cement-mixed soil strength is investigated in this research. The results showed that as the water-to-cement ratio increases, the influence of cementation and porosity on unconfined compressive strength decreases. The blended volume ratio is proposed as a new and adequate index for evaluating cement-mixed soil strength based on the experimental results. The blended volume ratio is the product of the void/cement volume ratio and the water/cement volume ratio. While the current index has not fully addressed the important effects of the water-to-cement ratio and porosity, the blended volume ratio allows describing the concurrent influences of porosity, cement amount, and water amount on the strength development. The experimental results showed that the cement-mixed soil strength is a function of the blended volume ratio. An empirical equation based on the blended volume ratio was then proposed for predicting the strength of cement-mixed soils. The validation of the proposed equation is verified by strength analysis for several different test data sets. A good agreement between measured and predicted results indicated that the proposed model is applicable to predict well the strength of cement-mixed soils.
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VERIFICATION ANALYSIS ON DYNAMIC CENTRIFUGAL MODEL TEST OF AN ABUTMENT WITH EPS BACKFILL Reviewed
Tsuyoshi NISHI, Tsuyoshi TORII, Tatsuro KUBOTA, Hiroyuki KYOKAWA, Junichi KOSEKI and Takeharu KONAMI
37 2022.12
Language：Japanese Publishing type：Research paper (scientific journal)
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Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay Reviewed
Misa Hiraga, Hiroyuki Kyokawa and Junichi Koseki
Canadian Geotechnical Journal 2022.11
Language：English Publishing type：Research paper (scientific journal)
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VERIFICATION ANALYSIS ON DYNAMIC CENTRIFUGAL MODEL TEST OF AN ABUTMENT WITH EPS BACKFILL
NISHI Tsuyoshi, TORII Tsuyoshi, KUBOTA Tatsuro, KYOKAWA Hiroyuki, KOSEKI Junichi, KONAMI Takeharu
Geosynthetics Engineering Journal 37 77 - 84 2022.10
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
According to a dynamic centrifugal model test of an abutment with EPS backfill, it has been reported a large force caused by collision of slabs acts on the abutment during an earthquake. This report presents the results of a 3-dimensional FEM analysis to confirm this phenomenon and to evaluate the effect of the force on the abutment. As a result, it was confirmed: the force acting on the abutment by the slabs is generated when the inertial force is directed to the back of the abutment; the behavior is similar to that of the past test; the effect of the action on the abutment was greater due to the inertial force than the earth pressure; and replacing the slabs with EPS partly is effective in mitigating the force acting on the abutment.
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Linking inherent anisotropy with liquefaction phenomena of granular materials by means of DEM analysis Reviewed
Masahide Otsubo, Sanjei Chitravel, Reiko Kuwano, Kevin J. Hanley, Hiroyuki Kyokawa, Junichi Koseki
Soils and Foundations 62 ( 5 ) 101202 - 101202 2022.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV
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Mechanical Behaviour and Stress-Strain Recovery Characteristics of Expanded Polypropylene Reviewed
Z. Maqsood, J. Koseki, H. Kyokawa
Geosynthetics International 2022.09
Language：English Publishing type：Research paper (scientific journal)
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A new index for the strength analysis and prediction of cement-mixed soils Reviewed
Pham, A. T., Kyokawa, H., Koseki, J. and Dias, D.
European Journal of Environmental and Civil Engineering 2022.06
Language：English Publishing type：Research paper (scientific journal)
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Evaluation of residual strength characteristics of reconstituted volcanic soil at Atsuma town, Hokkaido with stacked-ring shear tests Reviewed
Kenji Watanabe, Hiroyuki Kyokawa, Tomoya Onodera, Junichi Koseki and Yudai Aoyagi
Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering 267 2022.05
Language：English Publishing type：Research paper (international conference proceedings)
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Shaking table tests on bridge abutments reinforced by EPS and geogrid Reviewed
H. Kyokawa, Y. Yamazaki, J. Koseki, T. Konami, T. Nishi, T. Kubota
GEOSYNTHETICS INTERNATIONAL 29 ( 2 ) 163 - 173 2022.04
Language：English Publishing type：Research paper (scientific journal) Publisher：ICE PUBLISHING
This study is aimed at improving the seismic stability of bridge abutments. To study the effects of the combined use of a block of expanded polystyrene (EPS) and geogrid, a series of 1 g shaking table tests were conducted on a reduced-scale model of a cantilever-type bridge abutment and its backfill soil. The experiment results indicated that the base sliding and tilting of the wall can be further reduced by partly replacing the backfill soil with blocks of EPS, in combination with the use of the middle-height geogrid. Moreover, the relative settlement of the backfill soil at the interface with the wall could be reduced by the combined use of EPS and geogrid. Furthermore, the resultant normal force and rotational moment acting on the wall from the backfill soil during excitation also became small for the reinforced wall with both EPS and geogrid.
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Mechanism of wetting–induced deformation and failure of unsaturated soils Reviewed
Veerayut Komolvilas, Mamoru Kikumoto, Hiroyuki Kyokawa
International Journal for Numerical and Analytical Methods in Geomechanics 46 ( 6 ) 1064 - 1092 2022.02
Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley
The mechanisms of hydraulic collapse (wetting-induced deformation) are studied through a series of simulations using a model for unsaturated soils. The model is a critical state soil model extended for unsaturated soils using Bishop's effective stress tensor, the state boundary surface (SBS) moving with the change in the degree of saturation, and a rational soil-water characteristic curve that takes account of density and hydraulic hysteresis. Comparisons with published experimental data validate the proposed model. The simulation results show that the model adequately captures the hydraulic collapse behavior under both isotropic and anisotropic stress conditions. The effects of density, mean net stress, and deviatoric stress on the hydraulic collapse behavior are further investigated through a parametric calculation, and the mechanics of the wetting-induced instability are discussed. The effects of suction history, namely repeated wetting and drying cycles, on the deformation and failure, are also presented. The proposed model provides a validated method for modeling hydromechanical collapse in unsaturated soil and provides a better understanding of the mechanisms involved.
DOI： 10.1002/nag.3336
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A double structure model for hydro-mechano-chemical behavior of expansive soils based on the surface phenomena of mineral crystals Reviewed
Hiroyuki Kyokawa
Engineering Geology 294 106366 - 106366 2021.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV
It is well known that the typical swelling behavior of expansive soils is mainly caused by the nanoscale electrochemical phenomena on the surface of their main constituent mineral (i.e., smectite). In this study, the hydromechano-chemical (HMC) model for unsaturated expansive soils, which combines the macroscale soil skeleton behavior and the nanoscale interlaminar behavior of mineral crystals based on the surface phenomena is proposed within a double structure framework. The soil skeleton behavior is modeled using the Cam clay type model based on Bishop's effective stress, which considers the degree of saturation-induced hardening. Thus, it is capable of describing hydraulic collapse. Furthermore, the interlaminar behavior is demonstrated through the interlaminar force equilibrium of clay mineral crystals. To describe the swelling process during wetting, namely the crystalline and osmotic swellings, the hydration and osmotic forces acting on the mineral crystals are related to the degree of saturation. Through simulations of a series of the suction-controlled oedometer tests and the swelling pressure tests with various solutions for FEBEX bentonite, it is indicated that the proposed model demonstrates that it can comprehensively describe the typical HMC behavior of expansive soils.
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Mechanical behaviour and loading rate dependency of gypsum-mixed fine-grained soils
Masum Shaikh, Hiroyuki Kyokawa, Zain Maqsood, Md. Kamrul Ahsan, Junichi Koseki
PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GEOTECHNICAL ENGINEERING 176 ( 2 ) 166 - 177 2021.08
Language：English Publishing type：Research paper (scientific journal) Publisher：ICE PUBLISHING
Gypsum is regarded as an environmentally friendly binding material and is widely used to enhance the engineering properties of soft fine-grained soils. However, the time-dependent strength and deformation characteristics of fine-grained soils stabilised with gypsum have not yet been thoroughly investigated and rational evaluation of these characteristics will assist in the formulation of cost-effective and reliable design approaches. In this study, the time-dependent mechanical behaviours of gypsum-mixed fine-grained soil (GMFS) specimens were investigated under unconfined monotonic loading conditions, considering ageing periods of 3-90 days and five different loading rates (LR = 0.0005-1.0%/min). The results revealed that the unconfined compressive strength and stiffness of the GMFS specimens initially decreased with ageing and finally became stable after 14 days and 28 days of ageing for water/gypsum ratios of 1.30 and 1.60, respectively. Furthermore, the strength and stiffness of the GMFS specimens increased with an increase in LR.
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Experimental study on hardening characteristics and loading rate dependent mechanical behaviour of gypsum mixed sand Reviewed
Zain Maqsood, Junichi Koseki, Md Kamrul Ahsan, Masum Shaikh, Hiroyuki Kyokawa
Construction and Building Materials 262 2020.11
Publishing type：Research paper (scientific journal)
© 2020 Elsevier Ltd Gypsum is among the widely used construction materials, and is nowadays been considered for a variety of applications including soil stabilization, foundation works, grouting and brick manufacturing etc. Considering this prevalent utilization of gypsum in construction industry, a comprehensive study was conducted to examine the time-dependent strength and deformation characteristics of Gypsum Mixed Sand (GMS) by examining the hardening characteristics (up to nine months) and loading rate (up to five folds); under unconfined monotonic loading conditions. Effects of different factors including gypsum content, hemihydrate batches and interaction between ageing and loading rate were considered to rationally comprehend the time-dependent mechanical behaviour of GMS. The results revealed an obvious reduction in the peak strength of GMS during the initial month of ageing, and no further effects of ageing were witnessed afterwards. Moreover, a unique and significant dependency of strength and deformation on the loading rate was observed for GMS, and this behaviour was categorized into three different zones of loading rates.
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Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal phenomena Reviewed
Kyokawa, H.
E3S Web Conf., 2nd International Conference on Energy Geotechnics (ICEGT 2020) 205 2020.11
Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings)
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