Papers - KYOKOWA Hiroyuki
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Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal surface phenomena Reviewed
Hiroyuki Kyokawa
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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Experimental study on the mechanical behaviour of bounded geomaterials under creep and cyclic loading considering effects of instantaneous strain rates Reviewed
Zain Maqsood, Junichi Koseki, Yukika Miyashita, Jiren Xie, Hiroyuki Kyokawa
Engineering Geology 276 2020.10
Publishing type：Research paper (scientific journal)
© 2020 Elsevier B.V. Rational evaluation of the long-term performance of large-scale foundations, tunnels and natural slopes located in seismically active areas necessitates accurate assessment of the strength and deformation characteristics of bounded geomaterials, such as natural rocks and cemented soils, under creep and cyclic loading conditions. In the present study, a unique approach for examining the induced instantaneous loading/strain rates during unconfined creep and cyclic loading was adopted to unveil the effects of creep and cyclic loading on the mechanical behaviour of laboratory-produced bounded geomaterial, namely Gypsum Mixed Sand (GMS). At first, a series of unconfined monotonic tests at six different strain rates ranging from 5.3E+0 to 2.1E-5%/min were conducted on GMS. Subsequently, the mechanical behaviour of the GMS was examined under unconfined creep/sustained loading at four different stress levels. Further, these results were compared with a number of unconfined cyclic loading tests performed at different stress amplitudes. Identical patterns of the variations of axial strain accumulation and instantaneous strain rates were observed during the creep and cyclic loading. Based on the relationships between the failure stress/strain and the corresponding instantaneous strain rate, the mechanical behaviour of the GMS specimens subjected to creep and cyclic loading was found to be similar to each other, and was distinctively different than those under monotonic loading condition.
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A method for extending a general constitutive model to consider the electro‐chemo‐mechanical phenomena of mineral crystals in expansive soils Reviewed
Hiroyuki Kyokawa, Shintaro Ohno, Ichizou Kobayashi
International Journal for Numerical and Analytical Methods in Geomechanics 44 ( 6 ) 749 - 771 2020.04
Authorship：Lead author Publishing type：Research paper (scientific journal) Publisher：Wiley
© 2020 John Wiley & Sons, Ltd. The mechanical behavior of expansive soils varies according to the chemical composition of the pore fluid. It is well known that electrochemical phenomena on the surface of clay mineral crystals considerably affect their macrostructural behavior. In particular, a change in the pore fluid composition causes osmotic consolidation or swelling. In this study, a model is constructed to describe the characteristic behavior of expansive soils by coupling the interlaminar behavior of clay mineral crystals and the soil skeleton behavior. The interlaminar behavior is derived from the electro-chemo-mechanical coupling equilibrium of mineral crystals, and the soil skeleton behavior is given by a general elastoplastic constitutive model for soils. This modeling approach extends a general model to consider the electro-chemo-mechanical phenomena of mineral crystals. Oedometer tests with the replacement of the cell fluid and the swelling pressure and deformation tests on expansive clays are simulated with the proposed model. The simulation results indicate that the proposed method can reasonably represent the typical behavior of expansive soils.
DOI： 10.1002/nag.3026
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INFLUCENCES OF STRAIN HISTORY AND TIME PERIOD OF CREEP AFTER UNLOADING ON STRENGTH AND DEFORMATION CHARACTERISTICS OF EXPANDED POLYPROPYLENE BLOCK
Kyokawa Hiroyuki, Maqsood Zain, Koseki Junichi
Geosynthetics Engineering Journal 35 103 - 108 2020
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
The recoverability of an expanded polymeric bead foam is important to consider the mechanical property of the lightweight embankment using such foam which has been damaged due to an earthquake. In this study, the strength and deformation characteristics of the expanded polypropylene (EPP) block, which has a higher energy adsorption and recoverability, are investigated by a series of uniaxial compression tests with various strain rates, strain histories and the creep times after unloading. It could be observed from experiment results that the EPP block shows an elastoviscoplastic behavior, and the residual strain after unloading path decreases with time and the stiffness recovers simultaneously.
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Effects of loading rate on strength and deformation characteristics of gypsum mixed sand Reviewed
Zain Maqsood, Junichi Koseki, Hiroyuki Kyokawa
E3S Web of Conferences 92 2019.06
Publishing type：Research paper (international conference proceedings)
© The Authors, published by EDP Sciences. It has been unanimously acknowledged that the strength and deformation characteristics of bounded geomaterials, viz. cemented soils and natural rocks, are predominantly governed by the rate of loading/deformation. Rational evaluation of these time-dependent characteristics due to viscosity and ageing are vital for the reliable constitutive modelling. In order to study the effects of ageing and loading/strain rate (viscosity) on the behaviour of bounded geomaterials, a number of unconfined monotonic loading tests were performed on Gypsum Mixed Sand (GMS) specimens at a wide range of axial strain rates; ranging from 1.9E-05 to 5.3E+00 %/min (27,000 folds), and at different curing periods. The results indicate shifts in the viscous behaviour of GMS at critical strain rates of 2.0E-03 and 5.0E-01 %/min. In the light of this finding, the results are categorized into three discrete zones of strain rates, and the behaviour of GMS in each of these zones is discussed. A significant dependency of peak strength and stress-strain responses on strain rate was witnessed for specimens subjected to strain rates lesser than 2.0E-03 %/min, and the effects of viscosity/strain rate was found to be insignificant at strain rate higher than 5.0E-01%/min.
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Experimental and analytical investigations of volume change behaviour of saturated expansive soils in oedometer test Reviewed
Misa Hiraga, Hiroyuki Kyokawa, Junichi Koseki
E3S Web of Conferences 92 2019.06
Publishing type：Research paper (international conference proceedings)
© The Authors, published by EDP Sciences. The chemical and mechanical behaviours of saturated bentonite were experimentally and analytically investigated. A series of oedometer tests on saturated bentonite was conducted. By replacing the cell fluid during the oedometer test, one-dimensional osmotic consolidation and swelling behaviour were observed. The experimental results were simulated numerically using a constitutive model by considering the influence of electrochemical phenomena of clay mineral crystals on the macrostructural behaviour. It was concluded that the typical mechanical swellability of water-saturated bentonite in oedometer test is affected by a positive dilatancy behaviour due to the lower shear strength. After the osmotic consolidation test, a lateral contraction of the specimen in the oedometer was observed; this affected the compressibility during the subsequent mechanical consolidation. It was also concluded that the concentration of Na+ in the pore fluid affects the specific mechanical properties of bentonite.
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A system to measure permeability of unsaturated soils using local pin-type sensors in triaxial apparatus Reviewed
Jaylord U.Tan Tian, Junichi Koseki, Hailong Wang, Hiroyuki Kyokawa, Takeshi Sato
7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019 7 ( 2 ) 305 - 309 2019
Language：English Publishing type：Research paper (international conference proceedings) Publisher：The Japanese Geotechnical Society
© 2019 7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019. All rights reserved. This paper describes development of a triaxial permeameter apparatus for measuring coefficient of permeability of unsaturated soils by directly measuring the head difference between two points in a specimen using local pin-type sensors. The local pin-type sensors are made of stainless steel wrapped with membrane filter to measure suction. The apparatus includes the measurement of inflow rate by Mariotte's bottle and a weighing scale, while outflow rate is measured by burettes and a differential pressure transducer (DPT). Typical results show that the steady state flow condition can be achieved by using membrane filters to allow passage of water but prevent flow of free air. At steady state flow condition and reasonably stable measured head by the local pin-type sensors, permeability values were obtained by simple average.
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EVALUATION OF THE EFFECT OF THE NEW TYPE JOINT METAL AND COUNTERMEASURES AGAINST ROCKING BY FULL SCALE SHAKING TABLE TESTS OF EDO-EPS EMBANKMENT Reviewed
NISHI Tsuyoshi, TANI Mihiro, HAYASHI Natsuki, KUBOTA Tatsuro, KYOKAWA Hiroyuki, KOSEKI Junichi, KONAMI Takeharu
Geosynthetics Engineering Journal 34 ( 0 ) 153 - 160 2019
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
This paper presents the results of a full-scale shaking table experiment conducted to evaluate the earthquake resistance of a new type joint metal for the civil engineering method (EDO-EPS method) using polystyrene foam. At the same time, considering the influence of rocking of EPS embankment, which is a top heavy structure, we are studying countermeasures to reduce the deformation caused by this. As a result of the test, it was confirmed that the new type this can suppress the deformation compared to the old type metal joint. In addition, it was found that deformation due to rocking can be reduced by arranging the metal joints and providing steel plates in the floor slab.
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SHAKING TABLE TESTS ON COMBINED USE OF EPS BLOCK AND GEOGRID TO IMPROVE SEISMIC STABILITY OF ABUTMENTS Reviewed
KYOKAWA Hiroyuki, KAWASAKI Hiroki, KOSEKI Junichi, KONAMI Takeharu, NISHI Tsuyoshi, KUBOTA Tatsuro
Geosynthetics Engineering Journal 34 ( 0 ) 161 - 168 2019
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
In order to study the effects of combined use of EPS (block of expanded polystyrene), geogrid, and soil nailing to improve seismic stability of a bridge abutment, a series of 1g shaking table tests are conducted on a reduced-scale model of the abutment with girder and its backfill soil. It could be observed from experiment results that the horizontal displacement and tilting of the abutment and the relative settlement of the backfill soil at the interface with the abutment can be effectively reduced by setting the geogrid at the upper level of backfill and blocks of EPS at the middle level of backfill respectively. Moreover, the combination of soil nailing, geogrid and EPS can improve the seismic stability of abutment.
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Reconnaissance of the 2017 Puebla, Mexico earthquake Reviewed
Yolanda Alberto, Masahide Otsubo, Hiroyuki Kyokawa, Takashi Kiyota, Ikuo Towhata
Soils and Foundations 58 ( 5 ) 1073 - 1092 2018.10
Publishing type：Research paper (scientific journal)
© 2018 A normal-fault earthquake (Mw = 7.1) occurred in the state limit of Puebla and Morelos on September 19, 2017, exactly 32 years after the 1985 Michoacan Earthquake. A total of 5765 buildings suffered damage in Mexico City and about 300 in Puebla City. The authors carried out a reconnaissance of Mexico City, and some locations in the states of Puebla and Morelos, to identify the affected areas and the extent of damage. This report is a summary of the damage characteristics observed during the survey for both structural and geotechnical aspects. A series of microtremor measurements were taken to understand the ground motion characteristics in three key areas of the Mexico City Basin. The results are presented and compared to the data gathered from the accelerograph network available in Mexico, and the damage characteristics are discussed. Whenever relevant, the conditions before the earthquake are compared with the damage encountered by the inclusion of photographs. In order to understand the extent of the damage incurred by the 2017 earthquake, an overview is provided of the geological and geotechnical conditions of Mexico City, which is renowned for its soft soils and problems associated with those soils. Given that the 1985 Michoacan Earthquake established the standards for seismic design in Mexico City, this report provides background on the effects of the 1985 earthquake and comparisons are made with the Puebla earthquake.
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BEHAVIOR OF THE EPS EMBANKMENTS REINFORCED BY THE NEW JOINT METAL BINDER UNDER EARTHQUAKES Reviewed
NISHI Tsuyoshi, TSUKAMOTO Hideki, TANI Mihiro, HAYASHI Natsuki, KONAMI Takeharu, HAYASHI Taketo, KOSEKI Junichi, KYOKAWA Hiroyuki, YASUHARA Kazuya, KUBOTA Tatsuro
Geosynthetics Engineering Journal 33 ( 0 ) 191 - 196 2018
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
The small-scaled model tests have been carried out at laboratory to improve the stability of EPS embankments undergoing such gigantic earthquakes as Tohoku Great earthquake in 2011 and Kumamoto earthquake in 2016. In particular, an attempt was made to ensure whether the newly developed Joint Metal Binder (JMB) for enabling uniformity of each EPS block for embankments is eligible for attaining the purpose stated above. It is found out not only from lab. Tests but also from numerical analysis that the new JMB is available for increasing the stability of EPS embankments even under gigantic earthquakes.
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SHAKING TABLE TESTS ON COMBINED USE OF EPS BLOCK AND GEOGRID TO IMPROVE SEISMIC STABILITY OF RETAINING WALLS Reviewed
KYOKAWA Hiroyuki, YAMAZAKI Yutaro, KOSEKI Junichi, KONAMI Takeharu, NISHI Tsuyoshi, KUBOTA Tatsuro
Geosynthetics Engineering Journal 33 ( 0 ) 197 - 204 2018
Language：Japanese Publisher：Japan Chapter of International Geosynthetics Society
In order to study the effects of combined use of EPS (block of expanded polystyrene) and geogrid to improve seismic stability of a retaining wall, a series of 1g shaking table tests are conducted on a reduced-scale model of a cantilever type retaining wall and its backfill soil. It could be observed from experiment results that the base sliding and tilting of the wall can be further reduced by replacing partly 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. 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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Isogeometric analysis of THM coupled processes in ground freezing Reviewed
Yared W. Bekele, Hiroyuki Kyokawa, Arne M. Kvarving, Trond Kvamsdal, Steinar Nordal
Computers and Geotechnics 88 129 - 145 2017.08
Publishing type：Research paper (scientific journal)
© 2017 Elsevier Ltd An isogeometric analysis (IGA) based numerical model is presented for simulation of thermo-hydro-mechanically (THM) coupled processes in ground freezing. The momentum, mass and energy conservation equations are derived based on porous media theory. The governing equations are supplemented by a saturation curve, a hydraulic conductivity model and constitutive equations. Variational and Galerkin formulation results in a highly nonlinear system of equations, which are solved using Newton-Raphson iteration. Numerical examples on isothermal consolidation in plane strain, one-dimensional freezing and heave due to a chilled pipeline are presented. Reasonably good agreements were observed between the IGA based heave simulations and experimental results.
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Effect of slaking on direct shear behaviour of crushed mudstones Reviewed
Keshab Sharma, Takashi Kiyota, Hiroyuki Kyokawa
Soils and Foundations 57 ( 2 ) 288 - 300 2017.04
Publishing type：Research paper (scientific journal)
© 2017 This study investigates the effects of wetting and drying cycles, known as slaking, on the strength-displacement characteristics of crushed mudstone. A series of direct shear tests was conducted by simulating cyclic wetting and drying under different stress conditions using a modified direct shear apparatus. The effects of the stress ratio, the density of specimen, the initial water content before wetting, the slaking index, and the number of wetting and drying cycles on the test results was investigated. Experiments were also performed on less-slakable materials, including crushed sand stone, silica sand and glass beads, to compare the results with the crushed mudstone. Considerable creep displacement on the crushed mudstones was observed during both drying and wetting phases under the constant shear stress conditions. The creep displacement during the drying was more significant than during the wetting phase. The creep displacement accumulated with progressive wetting and drying cycles. The drying-induced displacement was observed when the water content became smaller than the amount of water absorption of the mudstone specimens. Correspondingly, a gradual decrease of the peak stress ratio was observed with the number of wetting and drying cycles. In contrast to the mudstones, the influence of cyclic wetting and drying on the crushed sand stone, silica sand and glass beads is almost negligible. A higher slaking index, a lower water content before wetting, and lower initial density accelerate the slaking of mudstones.
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Long-term mechanical analysis code considering chemical alteration for a TRU waste geological repositor Reviewed
MIHARA Morihiro, HIRANO Fumio, TAKAYAMA Yusuke, KYOKAWA Hiroyuki, OHNO Shintaro
Journal of Nuclear Fuel Cycle and Environment 24 ( 1 ) 15 - 26 2017
Language：Japanese Publisher：Division of Nuclear Fuel Cycle and Environment, Atomic Energy Society of Japan
<p> A computer program MACBECE has been developed to provide rigorous calculations of the long-term mechanical behavior of a TRU waste geological repository. Consideration is given to the expected chemical alteration of repository components, including cementitious materials and bentonite, and the mechanical interactions between repository and host rock. The long-term mechanical behavior of a TRU waste repository was evaluated in a deep soft rock site, where creep deformation is likely to occur from the initial construction phase to 10<sup>5</sup> years after repository closure. It was found that the stress didn't fall into a singularity of yield surface of the EC model applied to the mechanical behavior model of bentonite. The calculated displacement of the inner diameter of the repository, considering mechanical interaction between repository and host rock, was about half that of a result in 2nd progress report on R&D for TRU waste disposal in Japan.</p>
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Ultimate Lateral Resistance of Piles in Soils Based on Active Pile Length Reviewed
Mary Roxanne Aglipay, Kazuo Konagai, Takashi Kiyota, Hiroyuki Kyokawa
Geotechnical Hazards from Large Earthquakes and Heavy Rainfalls 525 2016.09
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Effect of in-situ sample quality on undrained cyclic strength and liquefaction assessment Reviewed
T. Kiyota, T. Ikeda, Y. Yokoyama, H. Kyokawa
Soils and Foundations 56 ( 4 ) 691 - 703 2016.08
Publishing type：Research paper (scientific journal)
© 2016 Japanese Geotechnical Society This study investigates the effects of quality of in-situ sandy samples, which were taken by a conventional tube sampling (TS) method, on liquefaction assessment. The sandy samples were retrieved from a loose fill layer and medium-dense Holocene deposit in young reclaimed land in Urayasu City where significant liquefaction occurred during the 2011 off the Pacific Coast of Tohoku Earthquake. First, a series of small strain measurements and undrained cyclic triaxial tests was conducted on the TS and reconstituted samples. Second, in order to investigate an applicability of the tested samples for the liquefaction assessment, an effective stress analysis was performed by use of soil parameters obtained from the examined samples. Input earthquake motions of the analysis are the 2011 off the Pacific Coast of Tohoku Earthquake and the 1987 Chiba Toho-oki Earthquake, the first and the second largest earthquakes the investigation site has experienced. The result of a sample quality assessment with the small strain shear moduli indicates that the TS sample retrieved from the Holocene deposit remains of high quality. In addition, for the reconstituted sample of the fill layer, since the small strain shear moduli of the sample are found to be nearly equal to those obtained at the field, it can be considered that the in-situ soil structure condition is reproduced in the reconstituted sample. According to an official report, the liquefaction resistance of the TS sample of the loose fill layer is RL20=0.38, which is much larger than that of medium-dense Holocene deposit (RL20=0.29) measured in this study. This is because the fill layer is so loose that the TS sample could have been strengthened due to disturbance during the sampling. On the other hand, the test result for the reconstituted sample of fill layer shows an appropriate level of liquefaction resistance (RL20=0.14). The results of the effective stress analysis using the soil parameters obtained from the TS sample of Holocene deposit and the reconstituted sample of fill layer show the most probable behaviors of the ground at the investigation site for both the 2011 off the Pacific Coast of Tohoku Earthquake and the 1987 Chiba Toho-oki Earthquake, which are consistent with the evidence reported after the earthquakes. The results indicate that the sample quality assessment by using a small strain shear moduli is applicable for the rational liquefaction assessment, and it would be possible to employ the reconstituted sample, which the small strain shear moduli are the same with the in-situ value, in substitution for a high quality sample.
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SLAKING PHENOMENA AND DEFORMATION BEHAVIOR OF CRUSHED MUDSTONE Reviewed
KIKUMOTO Mamoru, FUKUDA Takumi, KYOKAWA Hiroyuki
Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering) 72 ( 2 ) 126 - 135 2016
Language：Japanese Publisher：Japan Society of Civil Engineers
Two kinds of slaking tests, ordinary accelerated slaking tests and newly-developed 1d compression-slaking tests, are conducted on three kinds of mudstone in order to investigate slaking phenomena, namely, weathering due to cyclic process of wetting and drying. Variation in grading occurred by slaking and resulting, irreversible changes in mechanical characteristics are discussed based on the results of accelerated slaking tests. The experimental results of one-dimensional compression slaking test show that: particle crushing during compression process causes increase in compressibility; the wetting and drying cycles causes slaking-induced change of grading and this change causes significant volumetric compression. Finally, it is mentioned that constitutive modeling considering slaking is possible by describing evolution of grading due to slaking through the grading index <i>I<sub>G</sub></i> and linking maximum and minimum void ratio or critical state void ratio with <i>I<sub>G</sub></i>.
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IDENTIFICATION OF FACTORS AFFECTING LIQUEFACTION-INDUCED ROAD SUBSIDENCE IN URAYASU CITY EXTRACTED FROM DIGITA SURFACE MODELS Reviewed
SUYAMA Shota, KIYOTA Takashi, KONAGAI Kazuo, KYOKAWA Hiroyuki, UEMURA Kenta, HAMANAKA Ryo
Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering) 72 ( 1 ) 38 - 47 2016
Language：Japanese Publisher：Japan Society of Civil Engineers
The 2011 off Pacific coast of Tohoku Earthquake measuring Mw of 9.0 caused significant liquefaction in the Tokyo Bay area, which had been in its peak period of land reclamation projects since the World War II. In order to identify factors affecting liquefaction-induced damage to roads, the authors extracted values of road subsidence at total 224 points in Urayasu city, Chiba prefecture, from a subsidence map of the liquefied ground obtained from Airborne LiDAR surveys before and after the earthquake. The result indicates that the values of subsidence along arterial roads with thicker roadbeds are larger than those of residential roads. This feature is implemented in the empirical formula to describe road subsidence in terms of liquefaction potential index P<sub>L</sub>. In addition, improvement effects of liquefaction countermeasure are quantitatively examined on the subsidence map of the liquefied ground.
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Crack formation in cementitious materials used for an engineering barrier system and their impact on hydraulic conductivity from the viewpoint of performance assessment of a TRU waste disposal system Reviewed
Fumio Hirano, Yoshiteru Otani, Hiroyuki Kyokawa, Morihiro Mihara, Hiroyuki Shimizu, Akira Honda
Transactions of the Atomic Energy Society of Japan 15 ( 2 ) 97 - 114 2016
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Atomic Energy Society of Japan
© 2016 Atomic Energy Society of Japan, All Rights Reserved. The mechanical analysis code MACBECE2014 has been developed at the Japan Atomic Energy Agency (JAEA) to make realistic simulations of the physical integrity of the near field for performance assessment of the geological disposal of TRU waste in Japan. The MACBECE2014 code can be used to evaluate long-term changes in the mechanical behavior of the near field and any subsequent changes in the permeability of engineering barrier components, including crack formation in cementitious materials caused by expansion due to metal corrosion. Cracks in cementitious materials are likely to channel the flow of groundwater and so the represent preferred flow paths of any released radionuclides. Mechanical analysis was conducted using the MACBECE2014 code to investigate the concept of the TRU waste disposal system described in JAEA's Second Progress TRU Report. Simulated results of a disposal system with a bentonite buffer demonstrated that the low permeability of the engineering barrier system could be maintained for long time periods because the physical integrity of the bentonite buffer remained intact even if cracks in the cementitious components had formed locally. Simulated results of the disposal system with a concrete backfill instead of a bentonite buffer showed that crack formation leads to a significant increase in the permeability of the engineering barrier system.
