Papers - KYOKOWA Hiroyuki
-
Fundamental investigations of oxidation method of mud-rock containing pyrite Reviewed
2024.08
Language：Japanese Publishing type：Research paper (conference, symposium, etc.)
-
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.
-
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.)
-
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
-
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.
-
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
-
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.
-
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)
-
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)
-
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.
-
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
-
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)
-
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)
-
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)
-
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.
-
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
-
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.
-
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.
-
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.
-
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)
-
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)
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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>
-
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
-
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.
-
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>.
-
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.
-
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.
-
Effect of lattice-frame reinforced geosynthetics on seismic stability improvement of embankment on loose sand deposit Reviewed
M. Okamoto, T. Obara, Y. Nakajima, T. Yoshida, Y. Kitamoto, H. Kyokawa, Y. Sawada, K. Fujisaki
15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015: New Innovations and Sustainability 2324 - 2329 2015
Publishing type：Research paper (international conference proceedings)
The authors have developed a specific geosynthetic for reduction of differential settlement, composed of woven textile sheet and lattice frame of mortar injected fabric hoses, providing high bending rigidity. To examine the reinforcement effect of this geosynthetic system, called the lattice-frame reinforced (LFR) sheet, a series of dynamic centrifugal model tests and finite element analyses were carried out. The results showed that the LFR sheet was capable of reducing differential settlement due to seismic liquefaction and effective to reduce horizontal deformation of liquefiable layer as well as the case in which the improved zone was totally set under the embankment.
DOI： 10.3208/jgssp.IGS-28
-
Why do constitutive models using (p and q) have problems? Reviewed
T. Nakai, H. M. Shahin, M. Hinokio, H. Kyokawa
Geomechanics from Micro to Macro - Proceedings of the TC105 ISSMGE International Symposium on Geomechanics from Micro to Macro, IS-Cambridge 2014 2 683 - 688 2015
Publishing type：Research paper (international conference proceedings)
Most constitutive models have been formulated using the stress invariants (p and q) since the Cam clay model was developed. It is known that such models cannot describe uniquely the deformation and strength of soils under three different principal stresses. Then, the concept of tij has been proposed to describe uniquely the stress-strain behaviors in general three-dimensional (3D) stress conditions. In this paper, some inevitable problems of the ordinary models are firstly clarified. After then, the meaning of the tij concept and the method to apply tij concept to elastoplastic models are presented, since the details of the tij concept were described in the previous papers. This concept was found out from the idea that the frictional law essentially governs soil behavior. Using this concept, any kinds of one-dimensional models and/or three-dimensional models formulated by using (p and q) can be easily extended to general three-dimensional models. © 2015 Taylor & Francis Group.
DOI： 10.1201/b17395-122
-
Simple modeling of time-dependent behavior for structured soils Reviewed
Teruo Nakai, Hossain Md Shahin, Hiroyuki Kyokawa
Springer Series in Geomechanics and Geoengineering none 331 - 337 2015
Publishing type：Research paper (international conference proceedings)
© Springer International Publishing Switzerland 2015. A simple model to describe time-dependent behavior of various soils in 1D stress conditions is presented in this paper. The model is formulated not using the usual viscoplastic theories such as over-stress type and non-stationary flow surface type but utilizing the subloading surface concept by Hashiguchi (1980), and paying attention to the experimental results that the normally consolidation line (NCL) on the e-ln σ plane shift depending on the strain rate. The present model can describe various time-dependent behaviors not only of normally consolidated soil but also of over consolidated and naturally deposited soils in the same manner without violating the objectivities. The 1D model can easily be extended to the 3D using the tij concept (Nakai and Mihara 1984).
-
Simple modeling of time-dependent behavior for normally consolidated soil and structured soils Reviewed
T. Nakai, H. M. Shahin, H. Kyokawa
49th US Rock Mechanics / Geomechanics Symposium 2015 2 878 - 885 2015
Publishing type：Research paper (international conference proceedings)
Copyright 2015 ARMA, American Rock Mechanics Association. Simple models to describe time-dependent behavior of geomaterials in ID and 3D stress conditions are presented. After explaining previous viscoplastic models and the problems these models contain, a new time-dependent model is presented which is formulated not using usual viscoplastic theories but utilizing the subloading surface concept by Hashiguchi [1]. Based on experimental results, it has been shown that the normal consolidation line (NCL) and the critical state line (CSL) on the e - Inσ plane can shift vertically depending on the strain rate. The model can describe time-dependent behaviors of both normally consolidated unstructured as well as structured soils in the same manner. To describe the behavior of structured soil, a state variable, ρ, which represents the influence of density, and another state variable, ω, which represents the bonding effect, are introduced. After the formulation is explained in one-dimension to highlight the fundamental concepts of the model, it is extended to three-dimensions using the tij concept [2].
-
Simple Expression of the Ultimate Lateral Resistance of Piles on Sand based on Active Pile Length Reviewed
AGLIPAY Mary Roxanne, KONAGAI Kazuo, KIYOTA Takashi, KYOKAWA Hiroyuki
Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)) 71 ( 4 ) I_329 - I_336 2015
Language：Japanese Publisher：Japan Society of Civil Engineers
Simulation of the in-situ behavior of pile foundation is necessary in the seismic design and assessment for target structural integrity and performance during earthquakes. Generally, the pile behavior is governed by its deformation. For commonly used flexible piles, this deformation is observed to be significantly greater near the ground surface and becomes negligible with increasing depth. This region of significant deformation is defined as the active pile length, <i>L<sub>a</sub></i>. To simply investigate the behavior response of pile embedded in a homogeneous sandy soil, a plane strain condition using the 2D finite element method in nonlinear analysis was done. The subloading <i>t<sub>ij</sub></i> model is used to model the elasto-plastic behavior of the soil and the pile is modeled as a 2D continuum-based beam element. Based on the rigorous solution, piles reach the ultimate state of its side soil under large lateral deformations. In this case, a soil wedge can be observed being pushed up along this active pile length. Therefore, a simplified method using the active pile length as a key parameter to describe the ultimate lateral resistance of piles embedded in sand is presented for more practical approach in the seismic design and assessment of piles.
-
Numerical simulation of thermo-hydro-mechanically coupled processes during ground freezing and thawing Reviewed
H. Kyokawa, Y. W. Bekele
Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014 379 - 384 2015
Publishing type：Research paper (international conference proceedings)
Fully coupled Thermo-Hydro-Mechanical (THM) processes in the freezing and thawing phenomena of ground are studied numerically. Theoretical formulations for modeling the THM process of frozen soil are presented in this study. Fully saturated frozen soil composed of soil, water and ice is modeled as a homogeneous three-phase mixture (theory of multiphase mixture) and the governing equations of frozen ground are accordingly derived by combining the individual governing equations constituting phases with consideration of interaction between phases, especially water and ice phases. Those governing equations are solved by the finite element method with simple supplementary equations representing mechanical/hydraulic/thermal characteristics of frozen soil. From a parametric study on freezing process of one-dimensional soil column test, it is shown that the freezing volume change is affected by the hydraulic condition since the freezing consolidation occurs due to the changing of water pressure and effective stress at unfrozen area. © 2015 Taylor & Francis Group, London.
DOI： 10.1201/b17435-63
-
On thermo-hydro-mechanically (THM) coupled finite element modeling of ground freezing and thawing Reviewed
Y. W. Bekele, H. Kyokawa
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 2 959 - 964 2014
Publishing type：Research paper (international conference proceedings)
Fully coupled thermo-hydro-mechanical (THM) processes in the freezing and thawing phenomena of ground are studied numerically. Theoretical and numerical formulations for modeling the THM process is proposed. Porous media theory is used for deriving the governing equations in the theoretical formulation. A saturated frozen soil is assumed and this three-phase porous medium is modeled as a homogeneous continuum. The main governing equations derived in the theoretical formulation are the linear momentum balance equation, the energy balance equation and the mass balance equation for the pores. Supplementary equations in the theoretical formulation include thermodynamic equilibrium for pore pressures, a soil-water characteristic curve for the degree of water saturation, Darcy's law for water flow and Fourier's law for thermal conduction. The finite element method is used for the spatial discretization of the governing partial differential equations and the finite difference method for temporal discretization. The matrix equations are derived to accomodate both linear and nonlinear material behaviors for the constitutive equations of the soil skeleton. © 2014 Taylor & Francis Group, London.
-
Rational expression of time-dependent behavior from normally consolidated soil to naturally deposited soil Reviewed
T. Nakai, H. M. Shahin, H. Kyokawa
18th International Conference on Soil Mechanics and Geotechnical Engineering: Challenges and Innovations in Geotechnics, ICSMGE 2013 1 255 - 258 2013
Publishing type：Research paper (international conference proceedings)
Fundamental concepts of the ordinary elasto-viscoplastic modelings, which are the non-statonary flow surface model and the over-stress type model, are explained in one-dimensional (1D) compression of normally consolidated soil for easy understading. Then, a new approach to describe various time-dependent behaviors of soils is presented extending the advanced elastoplasitic theory based on the subloading surface concept without employing usual elasto-viscoplastic theories. Throughout the simulations of various time-dependent behaviors of normally consolidated clay, the features of these three types of time-denpendent models are clarified. In addtoin, 1D anlyses using the proposed model are carried out not only for normally consolidated clay but also for over-consolidated clay and strauctured clay such as nuturally deposited clay. The analytical results simulate well the features of time-dependent behavior of various clays including the delayed settlement of sturctured clay.
-
Significance of t<inf>ij</inf> concept in constitutive modeling of geomatrials Reviewed
T. Nakai, H. M. Shahin, M. Hinokio, H. Kyokawa
Computational Geomechanics, COMGEO III - Proceedings of the 3nd International Symposium on Computational Geomechanics 108 - 122 2013
Publishing type：Research paper (international conference proceedings)
© 2013 Computational Geomechanics, COMGEO III - Proceedings of the 3nd International Symposium on Computational Geomechanics. All rights reserved. Simple and unified method to describe stress-strain behavior in general three-dimensional stress condition, which has been called the tij concept, was presented by Nakai & Mihara (1984). Since this concept is based on the idea that the frictional law essentially governs soil behavior, its meaning is very clear. Using this concept, any kind of one-dimensional model and/or three-dimensional model formulated by using (p and q) can be easily extended to general three-dimensional conditions. Method for formulating the constitutive model using the tij concept and the meaning of the tij operator are reviewed. The validity of this concept is also checked by simulation of various types of shear tests in general three-dimensional conditions.
-
Liquefaction-induced damage on the reclaimed area in Urayasu city and the result of SWS test Reviewed
YOKOYAMA Yutaka, KYOKAWA Hiroyuki, KONDO Yasuto, KIYOTA Takashi
SEISAN KENKYU 64 ( 6 ) 853 - 857 2012
Language：Japanese Publisher：Institute of Industrial Science The University of Tokyo
The 2011 off the Pacific coast of Tohoku Earthquake induced liquefaction causing damage to residences and buried lifelines in the entire filled ground in Urayasu city, Chiba prefecture. Since immediately after the earthquake, authors have conducted SWS test at several monthly intervals at the site in the particularly serious damaged area. The result of SWS tests suggests that the fill sandy soil having a high fine content was liquefied, and the penetration resistance of its layer which had remarkably decreased due to liquefaction recovered two month after the earthquake. Moreover, the possibility of re-liquefaction is discussed based on the value of liquefaction resistance in this report. [This abstract is not included in the PDF]
-
Survey report on Liquefaction-induced damage in Urayasu city caused by The 2011 of the Pacific coast of Tohoku Earthquake Reviewed
KYOKAWA Hiroyuki, KIYOTA Takashi, KONDO Yasuto, KONAGAI Kazuo
Japanese Geotechnical Journal 7 ( 1 ) 265 - 273 2012
Language：Japanese Publisher：The Japanese Geotechnical Society
On March 11<sup>th</sup>, 2011, the Pacific coast of Tohoku Earthquake hit east Japan. The earthquake-induced liquefaction caused severe damage to residences and buried lifelines in Tokyo bay area. This report summarizes result from field investigation including SWS test in Urayasu city, Chiba prefecture. Grading analysis was also conducted on in situ samples and boiled sands which were retrieved at liquefaction sites. From these investigations, this report shows the liquefaction characteristic causing the wide range of serious subsidence in reclaimed area in Urayasu city. Comparing with the result of investigations in Christchurch city, New Zealand which has suffered the damage of re-liquefactions by the 2010-2011 Canterbury Earthquake, the possibility of re-liquefaction in Urayasu is discussed in this report.
DOI： 10.3208/jgs.7.265
-
Description of time-dependent behavior of soils using subloading surface concept Reviewed
Nakai Teruo, Shahin Hossain Md., Kikumoto Mamoru, Kyokawa Hiroyuki
NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan 61 ( 0 ) 108 - 108 2012
Language：Japanese Publisher：National Committee for IUTAM
As an application of the simple and advanced method for modeling of soil features developed in our laboratory, one-dimensional and three-dimensional inviscid models are extended to ones which can describe various time-dependent behaviors of soils not using the existing viscoplastic theories but introducing and revising the subloading surface concept by Hashiguchi. The performance of the proposed models are confirmed through the simulations of various time-dependent behaviors on normally and over consolidated clays and naturally deposited clay
-
SURFACE RUPTURE OF THE NORMAL SEISMIC FAULTS AND SLOPE FAILURES APPEARED IN APRIL 11<sup>th</sup>, 2011 FUKUSHIMA-PREFECTURE HAMADOORI EARTHQUAKE Reviewed
KAZMI Zaheer Abbas, KONAGAI Kazuo, KYOKAWA Hiroyuki, TETIK Cigdem
Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)) 68 ( 4 ) I_1285 - I_1292 2012
Language：English Publisher：Japan Society of Civil Engineers
On April 11<sup>th</sup>, 2011, Iwaki region of Fukushima prefecture was jolted by Fukushima-Prefecture Hamadoori Earthquake. Surface ruptures were observed along causative Idosawa and Yunotake normal faults. In addition to numerous small slope failures, a coherent landslide and building structures of Tabito Junior High School, bisected by Idosawa Fault, were found along the causative faults. A precise digital elevation model of the coherent landslide was obtained through the ground and air-born LiDAR surveys. The measurements of perimeters of the gymnasium building and the swimming pool of Tabito Junior High School have shown that ground undergoes a slow and steady/continual deformation.
-
ROAD BRIDGES IN MINAMI-SANRIKU WASHED AWAY IN THE MARCH 11<sup>th</sup> 2011 GREAT EAST JAPAN EARTHQUAKE AND TSUNAMI Reviewed
AGLIPAY Mary Roxanne I., KONAGAI Kazuo, KYOKAWA Hiroyuki, KESHAB Sharma
Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)) 68 ( 4 ) I_1307 - I_1314 2012
Language：English Publisher：Japan Society of Civil Engineers
On March 11<sup>th</sup>, 2011, Minami-Sanriku, located in the northeastern coast of Japan was severely inundated by the tsunami that followed the Great East Japan Earthquake on March 11, 2011. Road bridges near the coastlines in this area have been extensively damaged with their decks being overturned or carried over long distances. An attempt was made to deduce as rational scenarios as possible before remaining debris was cleaned up. Though the reasons for the washout of bridges can be many and complex, it is to be noted that bridge decks have hollows for the optimum light-weight solution, which fact eventually allowed the bridge decks to be carried over remarkable distances. Poor connection details and cavities, hollows between deck beams, are considered to have facilitated overturning due to uplift forces.
-
A simple and unified one-dimensional model to describe various characteristics of soils Reviewed
Teruo Nakai, Hossain M.D. Shahin, Mamoru Kikumoto, Hiroyuki Kyokawa, Feng Zhang, Marcio M. Farias
Soils and Foundations 51 ( 6 ) 1129 - 1148 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：The Japanese Geotechnical Society
A simple and unified constitutive model for soils, considering various effects such as the influences of density, bonding, time dependent behavior and others, is presented in this paper. The elastoplastic behavior of over consolidated non-structured soils under a one-dimensional stress condition is firstly presented by introducing a state variable that represents the influence of density (stage I). To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on density and bonding as the main factors that affect the response of this type of soil, because it can be considered that soil a skeleton structure which is in a looser state than that of a normally consolidated soil is formed by bonding effects (stage II). Furthermore, a simple method is presented which allows for other soil characteristics to be considered, such as time and temperature dependency, and the effect of suction in unsaturated soils. Experimental observations show that the normally consolidated line (NCL) in the void ratio-stress relation (e.g., e-ln s curve) shifts depending on the change of strain rate, temperature, suction and others (stage III). The validation of the model at stages I and II is demonstrated by simulating one-dimensional consolidation tests for normally consolidated, over consolidated and natural clays. The applicability of the model at stage III is verified not only by the simulations of time-dependent behavior of clays in one-dimensional element tests but also by the soil-water coupled finite element analysis of oedometer tests as a boundary value problem. The extension from one-dimensional models to three-dimensional models is easily achieved by defining the yield function using stress invariants instead of one-dimensional stress 'σ' and by assuming an appropriate flow rule in stress space. The details of the modeling in general three-dimensional stress conditions will be described in another paper (Nakai et al., 2011).
-
A simple and unified three-dimensional model to describe various characteristics of soils Reviewed
Teruo Nakai, Hossain M.D. Shahin, Mamoru Kikumoto, Hiroyuki Kyokawa, Feng Zhang, Marcio M. Farias
Soils and Foundations 51 ( 6 ) 1149 - 1168 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：The Japanese Geotechnical Society
A simple and unified model to describe some features of soil behavior in one dimensional condition is presented in another related paper (Nakai et al., 2011). In the present paper, this one-dimensional model is extended to describe not only the soil features explained in the related paper three-dimensionally (3D), but also to explain other soil features found in multi-dimensional conditions, such as shear behavior considering the influence of intermediate principal stress on the deformation and strength of soils, and the positive and negative soil dilatancy. Firstly, the first step in extending any kind of one-dimensional model to a three-dimensional one is explained in detail: the significance of tij concept and its stress invariants (tN and tS) is explained and compared with the idea of ordinary stress invariants (p and q) used in the Cam clay model. Then, the advanced elastoplastic relations (stages I to III) in the one-dimensional condition presented in the related paper are re-formulated as three-dimensional models-e.g., a model for over consolidated soil, a model for structured soil and a model which considers time-dependent behavior. The three-dimensional models for over consolidated soil (stage I) and structured soil (stage II) are formulated so as to coincide with the subloading tij model developed by Nakai and Hinokio (2004) and by Nakai (2007), respectively. The validity of the models in stage I and stage II is checked by simulations of various shear tests for sands with different void ratios and for over consolidated and natural clays under drained and undrained conditions. The model in stage III is verified by simulations of shear tests with different strain rates, and by simulating creep tests and others, not only for normally consolidated clay but also for non-structured and structured over consolidated clays under drained and undrained conditions.
-
Survey report on damage of landfill in Miyagi Prefecture caused by the 2011 Tohoku earthquake Reviewed
KIYOTA Takashi, KYOKAWA Hiroyuki
SEISAN KENKYU 63 ( 6 ) 709 - 715 2011
Language：Japanese Publisher：Institute of Industrial Science The University of Tokyo
The Tohoku earthquake hit the east Japan on March 11<sup>th</sup>, 2011. Many coastal areas along Pacific Ocean were destroyed by tsunami, while a large number of geo-disasters was caused by the earthquake over a large extent of area in the eastern Japan. In Miyagi prefecture, there are many artificial earth fills for housing estate that suffered from serious earthquake-induced damage. During the construction of these areas, cut-and-fill work was carried out, and most of the significant earthquake-induced damage could be found in a fill part. This report summarizes damage aspects of landfills that have so far been found by the author’s field investigations. [This abstract is not included in the PDF]<br>
-
Simple modelling of stress-strain behaviour of unsaturated soils Reviewed
M. Kikumoto, H. Kyokawa, T. Nakai
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering 2011
Publishing type：Research paper (international conference proceedings)
A simple constitutive model taking account of the necessary features of unsaturated soils is proposed by extending an elastoplastic model for saturated soils. The proposed model is formulated using the Bishop's effective stress and the critical state friction angle is thus assumed to be constant. In the model, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidation line in the plane of mean effective stress and void ratio, by which the typical volumetric behaviours of unsaturated soils are properly described. A simple method for extending a classical water characteristics curve assuming a unique relationship between suction and degree of saturation to incorporate the effects of hydraulic hysteresis and density is also proposed. In this paper, mechanisms of hydraulic collapse and compaction of soils are discussed through a series of simulations by the proposed model.
-
New approach for modeling time-dependent behavior of geomaterials Reviewed
T. Nakai, H. M. Shahin, M. Kikumoto, H. Kyokawa, F. Zhang, M. M. Farias
Computational Geomechanics, COMGEO II - Proceedings of the 2nd International Symposium on Computational Geomechanics 49 - 62 2011
Publishing type：Research paper (international conference proceedings)
A simple method to describe time-dependent behavior for various kinds of soils is presented. The model is formulated not using usual viscoplastic theories but utilizing the subloading surface concept by Hashiguchi (1980) and paying attention to the experimental results, which show that the normal consolidation line (NCL) and the critical state line (CSL) on the e - lnσ plane shift depending on the strain rate. The formulation is first explained in one-dimensional conditions in order to understand the method easily. After that, using the tij concept proposed by Nakai and Mihara (1984), the one-dimensional model is extended to a three-dimensional one. The validity of the present model is verified using various kinds of simulations of time-dependent behavior in both conditions - e.g., onedimensional compression tests under different strain rate, oedometer tests including secondary consolidation, creep and stress relaxation tests, constant strain rate triaxial tests and others.
-
Modeling of one-dimensional consolidation behavior for clays Reviewed
T. Nakai, H. M. Shahin, H. Kyokawa, Y. Miyahara
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering 2011
Publishing type：Research paper (international conference proceedings)
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in one-dimensional stress condition is presented by introducing a state variable (ρ) to represent the influence of density and another state valuable (ω) which represents the imaginary increase of density by boding effect. Then, another state variable (ψ) is introduced to describe the time dependent behavior, the temperature dependent behavior, the effect of saturation and others. Here, the state valuable (ψ) has a function which shifts the normally consolidation line (NCL) due to the strain rate, temperature, saturation and others. Although the models are formulated in one-dimensional condition in this paper, it is possible to extend them to three-dimensional ones using t ij concept, easily.
-
Bridges washed away by tsunami in Minamisanriku, Miyagi Prefecture in the March 11<sup>th</sup> 2011 Great East Japan Earthquake Reviewed
AGLIPAY Mary Roxanne I., KESHAB Sharma, KYOKAWA Hiroyuki, KONAGAI Kazuo
SEISAN KENKYU 63 ( 6 ) 723 - 727 2011
Language：English Publisher：Institute of Industrial Science The University of Tokyo
-
A simple method to consider density and bonding effects in modeling of geomaterials Reviewed
Teruo Nakai, Mamoru Kikumoto, Hiroyuki Kyokawa, Hassain M. Shahin, Feng Zhang
Springer Series in Geomechanics and Geoengineering 5 91 - 111 2011
Publishing type：Research paper (scientific journal)
A simple method to describe stress-strain behavior of structured soils under normally and over-consolidated states in one-dimensional stress condition is first presented by introducing a state variable to represent the influence of density. To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on the density and the bonding as the main factors that affect a structured soil, because it can be considered that the soil skeleton structure in a state which is looser than that of a normally consolidated soil is formed by bonding effects. The extension from one-dimensional model to three-dimensional model can be done only by defining the yield function using the invariants of modified stress 'tij' instead of one-dimensional stress 'σ' and assuming the flow rule in modified stress space tij. © Springer-Verlag Berlin Heidelberg 2011.
-
A simple elasto-plastic model for unsaturated soils and interpretations of collapse and compaction behaviours Reviewed
M. Kikumoto, H. Kyokawa, T. Nakai, H. M. Shahin
Unsaturated Soils - Proceedings of the 5th International Conference on Unsaturated Soils 2 849 - 855 2011
Publishing type：Research paper (international conference proceedings)
Stress-strain behaviour of unsaturated soils seems rather different from that of saturated ones. It should however be described properly because soil may lie under an unsaturated state in the actual field. In the present study, a model taking account of the necessary characteristics of unsaturated soils is proposed by extending an existing model for saturated ones based on the Bishop's effective stress. In the model, variation in the degree of saturation is estimated by a newly proposed model for water retention curve considering the effects of hydraulic hysteresis and density, and the increase in the degree of saturation is linked with downward movement of normally consolidation line in the mean effective stress vs. void ratio plane in order to describe the typical behaviours of unsaturated soils. In the present paper, mechanisms of consolidation, soaking and compaction behaviours of unsaturated soils are discussed through the simulations by the proposed model. © 2011 Taylor & Francis Group, London.
-
Elastoplasitc constitutive model for soils considering the temperature dependency Reviewed
Kikumoto Mamoru, Kyokawa Hiroyuki, Nakai Teruo, Shahin Hossain.Md., Ban Akimasa
NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan 60 ( 0 ) 41 - 41 2011
Language：Japanese Publisher：National Committee for IUTAM
Geotechnical and geoenvironmental problems related with thermo-mechanical behaviour of soils have been increased as a result of various interests in geotechnical applications such as nuclear waste disposal, heat storage, development of marine underground resources, high-voltage cables and other geothermal structures. Although several researchers have been conducted coupled thermo-hydro-mechanical (THM) analyses in order to investigate the geothermal behaviour of ground, the THM characteristics of geomaterials have not been fully understood and have not been properly described by a constitutive model for soils. In the present study, the effects of temperature on the stress-strain characteristics of saturated soils are firstly discussed based on the past experimental researches on the THM behaviour and a simple method to describe the temperature-dependent behaviour for various kinds of soils is then proposed in the context of elastoplastic framework.
-
Elastoplastic constitutive model of soil considering the saturation and unsaturation characteristics Reviewed
Kyokawa Hiroyuki, Kikumoto Mamoru, Nakai Teruo, Tatematsu Kazunori, Koike Mana, Tsukamoto Kohei
NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan 60 ( 0 ) 48 - 48 2011
Language：Japanese Publisher：National Committee for IUTAM
Although stress-strain characteristic of unsaturated soil is complicated and rather different from that of saturated soil, it should be described properly by a constitutive model for soils because soil usually stays under an unsaturated condition in actual field. In the current study, a simple elastoplastic model for saturated soil is extended to one applicable to unsaturated soils. The proposed model is formulated using the Bishop's effective stress and the residual strength is, therefore, assumed to be constant. In the proposed model, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidated line in the compression plane of mean effective stress and void ratio, by which the typical volumetric and distortional behaviors of unsaturated soils are properly described. In the present paper, the outline of the proposed model is explained and applicability of the model is discussed through typical results of simulations.
-
Simple modeling of stress-strain relation for unsaturated soil Reviewed
H. Kyokawa, M. Kikumoto, T. Nakai, H. Shahin
Geotechnical Special Publication ( 202 GSP ) 17 - 25 2010
Publishing type：Research paper (international conference proceedings)
Though stress-strain characteristics of unsaturated soils are complicated and rather different from those of saturated soils, it should be described properly by a constitutive model for soils because soil usually stays under an unsaturated condition in actual field. In the current study, a simple elastoplastic model for saturated soil is extended to one applicable to unsaturated soils. The proposed model is formulated using the Bishop's effective stress and the residual strength is, therefore, assumed to be constant. In the proposed model, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidated line in the compression plane of mean effective stress and void ratio, by which the typical volumetric and distortional behaviors of unsaturated soils are properly described. In addition, a simple method to extend classical water retention curves such as van Genuchten's equation to be able to incorporate the influences of suction histories and density is proposed and applied to the proposed model. In the present paper, the outline of the proposed model is explained and applicability of the model is discussed through typical results of simulations. © 2010 ASCE.
DOI： 10.1061/41103(376)3
-
Description of stress-induced anisotropy of soils by modified stress within an isotropic hardening elastoplastic model Reviewed
KYOKAWA Hiroyuki, KIKUMOTO Mamoru, NAKAI Teruo
Japanese Geotechnical Journal 5 ( 4 ) 533 - 544 2010
Language：Japanese Publisher：The Japanese Geotechnical Society
The various stress change with rotating principal axes act on soil in actual ground. The distribution of the interparticle contact normals, meanwhile, gradually tends to concentrate towards the direction of the major principal stress <i>σ</i><sub>1</sub> when that of anisotropic stress acts on soil skeleton. And then, the stiffness of soil in the direction of major principal stress relatively increases. In ordinary model, such an induced anisotropy is considered by applying kinematic / rotational hardening rule in ordinary stress space. On the other hand, a new method, in which the induced anisotropy of soil is described simple and general isotropic hardening model by applying the modified stress which reflects the fabric change due to the variations of the intermediate principal stress and the stress histories, is developed in this study. The validity of the proposed model is verified by comparison with the experimental results of true triaxial tests on medium dense sand. It is shown that the proposed model, which obeys isotropic hardening rule and follows associated flow rule in <i>t<sub>ij</sub></i><sup>*</sup> space, suitably considers the influence of the intermediate principal stress and the past stress history simultaneously and properly reproduces the test results under various complicated three-dimensional stress path.
DOI： 10.3208/jgs.5.533
-
A SIMPLE DESCRIPTION OF THE STRESS-STRAIN AND HYDRAULIC BEHAVIOURS OF UNSATURATED SOIL Reviewed
H. Kyokawa, M. Kikumoto, Teruo Nakai
RECENT DEVELOPMENTS OF GEOTECHNICAL ENGINEERING 74 - 81 2010
Language：English Publishing type：Research paper (international conference proceedings) Publisher：JAPANESE GEOTECHNICAL SOC
Stress-strain behaviour of unsaturated soils is rather complex and quite different from that of saturated soils. However, it should be described properly by a constitutive model for soils because soil usually lies under an unsaturated state in the actual field. In the current study, a simple elastoplastic model for saturated soil is extended to one considering the necessary characteristics of unsaturated soils. The proposed model is formulated using the Bishop's effective stress and the residual strength is, therefore, assumed to be constant. In order to describe the behaviour of unsaturated soils, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidated line in the compression plane of mean effective stress and void ratio, by which the typical volumetric behaviours of unsaturated soils can be properly described. In addition, a simple method to extend classical water retention curves such as van Genuchten's equation is proposed in order to incorporate the influences of suction histories and density and it is applied to the proposed model. Because the volumetric behaviours of unsaturated soils such as consolidation and collapse behaviours are mainly focused on in the present paper, a simplified one-dimensional formulation of the elastoplastic constitutive model is explained. The validity of the proposed model is discussed through typical results of simulations.
-
MODELING OF TIME-DEPENDENT BEHAVIOR OF CLAY IN ONE-DIMENSIONAL CONSOLIDATION Reviewed
H. M. Shahin, T. Nakai, M. Kikumoto, H. Kyokawa, Y. Miyahara
RECENT DEVELOPMENTS OF GEOTECHNICAL ENGINEERING 54 - 61 2010
Language：English Publishing type：Research paper (international conference proceedings) Publisher：JAPANESE GEOTECHNICAL SOC
One-dimensional consolidation tests on clay have been performed using a one-dimensional model which can consider the effects of density, bonding and time. The model can explain strain rate effect, stress relaxation characteristics and creep characteristics of soils comprehensively without fitting the model for a particular phenomenon. The model can also describe other characteristics of soils such as secondary compression, delayed consolidation and consolidation characteristics of naturally deposited soils. Here, consolidation behavior of clay has been investigated varying the density of soil having different states of bonding. Varying the thickness of soil samples, the dependency of the sample height on the consolidation behavior has been checked as well. It is found that the model can explain well the behavior of secondary consolidation of naturally consolidated soil, overconsolidated soil and structured soil.
-
Elastoplastic modeling of geomaterials considering the influence of density and bonding Reviewed
T. Nakai, H. Kyokawa, M. Kikumoto, H. M. Shahin, F. Zhang
Prediction and Simulation Methods for Geohazard Mitigation 367 - 373 2009.01
Publishing type：Part of collection (book)
© 2009 Taylor & Francis Group, London. To understand easily the method for modeling the behavior of structured soils, one-dimensional description of elastoplastic behavior is firstly shown, and then it is extended to a constitutive model in general three-dimensional stress conditions. To describe the stress-strain behavior of structured soils, attention is focused on the density and the bonding as the main factors that affect a structured soil, because it can be considered that the soil skeleton structure in a state, which is looser than that of a normally consolidated soil, is formed by bonding effects including interlocking between soil particles and others. The extension from one-dimensional model to three-dimensional model can be done only by defining the yield function using the invariants of modified stress ‘tij’ instead of one-dimensional stress ‘σ’ and assuming the flow rule in modified stress space tij.
-
A unified method to describe the influences of intermediate principal stress and stress history in constitutive modelling Reviewed
M. Kikumoto, T. Nakai, H. Kyokawa, F. Zhang, H. M. Shahin
Geotechnics of Soft Soils - Focus on Ground Improvement - Proceedings of the 2nd International Workshop on Geotechnics of Soft Soils 151 - 157 2009
Publishing type：Research paper (international conference proceedings)
A simple and unified method for considering the influences of the intermediate principal stress and the stress histories on the deformation and the strength of soils, which obeys isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress tij, which was proposed before by our group to describe the influence of the intermediate principal stress, is extended to a new stress tensor tij* to consider the fabric change of soils due to the variations of the intermediate principal stress and the stress histories. The evolution rule of tij* is established referring to past experimental evidences. In this paper, the modified stress tij* is applied to the isotropic hardening elastoplastic model named subloading tij model. The proposed model is verified by comparing the calculated results with the experimental results of true triaxial tests and directional shear tests on medium dense sand. © 2009 Taylor & Francis Group.
-
New description of stress-induced anisotropy using modified stress Reviewed
M. Kikumoto, T. Nakai, H. Kyokawa
Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering: The Academia and Practice of Geotechnical Engineering 1 550 - 553 2009
Publishing type：Research paper (international conference proceedings)
A simple and comprehensive method for describing the influences of the intermediate principal stress σ 2 and the stress histories on the deformation and the strength of soils, which assumes associated flow rule and obeys isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress t ij, which was proposed to describe the influence of σ 2, is extended to the proposed modified stress tensor t ij* to consider the fabric change of soils due to the stress histories as well as the variation of σ 2. In this paper, the modified stress t ij* is applied to an elastoplastic model named subloading t ij model. The proposed model is verified by comparing the calculated results with the experimental results on sand. © 2009 IOS Press.
-
Modelling the influence of density and bonding on geomaterials Reviewed
T. Nakai, F. Zhang, H. Kyokawa, M. Kikumoto, H. M. Shahin
Geotechnics of Soft Soils - Focus on Ground Improvement - Proceedings of the 2nd International Workshop on Geotechnics of Soft Soils 65 - 76 2009
Publishing type：Research paper (international conference proceedings)
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in three-dimensional stress condition is presented. Based on an idea that structured soils can be made due to a kind of bonding effects between soil particles, a simple elastoplastic model is formulated by extending subloading tij model developed before. First, a new interpretation of subloading surface concept for describing the influence of density and/or confining pressure is described. Then, a method to take into consideration the effect of bonding on the soil behavior in constitutive modeling is developed. By introducing this method for considering bonding to the subloading tij model, the stress-strain behavior of structured soils is described. The validity of the proposed model is confirmed by numerical simulation of oedometer tests and undrained shear tests on structured clay. © 2009 Taylor & Francis Group.
-
地盤材料の諸特性の簡単且つ統一的なモデリング-密度,ボンディング,時間効果特性を中心として- Reviewed
京川 裕之
応用力学論文集 12 371 - 382 2009
Publishing type：Research paper (scientific journal)
-
A method for considering induced anisotropy in an isotropic hardening model Reviewed
Kikumoto Mamoru, Nakai Teruo, Zhang Feng, Kyokawa Hiroyuki, Ishihara Takahiro
NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan 57 ( 0 ) 156 - 156 2008
Language：Japanese Publisher：National Committee for IUTAM
Soil is a kind of material which behaves anisotropically depending on stress histories. This characteristic of soil is usually called "stress-induced anisotropy". Such stress-induced anisotropy of soil is often modeled by applying kinematic / rotational hardening rule. On the other hand, though ordinary models which obey isotropic hardening rule are simpler than kinematic hardening models, they are not incapable of describing the stress-induced anisotropy. Satake, one of the authors and some researchers previously showed the possibility that even isotropic hardening model can describe the stress-induced anisotropy by using fabric tensor which suitably considers the influence of stress histories and reflecting it on the stress variables. It is, however, difficult to quantitatively estimate the variation of the fabric. Therefore, appropriate models formulated with the fabric tensor, which can be applied to the analysis of boundary value problems, have not been developed. Our research group proposed the modified stress tensor tij, by which we can properly consider the influence of intermediate principal stress on the deformation and the strength of soils. In addition to this, it has been noticed by experimental evidence and theoretical consideration that tij is the modified stress which reflects suitably the fabric tensor under monotonic loading paths. A new isotropic hardening model is proposed in which the induced anisotropy is taken into account by extending the concept of the modified stress tensor tij. As the results, this model is able to take into account the influence of various stress histories in general stress conditions. The influence of intermediate principal stress and that of stress histories are inclusively considered by the extended modified stress tij*. The validity of the model is verified by comparing the results calculated by the model with experimental results not only in anisotropic and shear tests on soils with stress histories under triaxial stress conditions but also in cyclic tests with the change of principal stress directions under three different principal stresses.
-
Description of induced anisotropy of soils using isotropic hardening rule in modified stress space Reviewed
M. Kikumoto, H. Kyokawa, T. Nakai, F. Zhang, M. Hinokio
Proceedings of the 10th International Symposium on Numerical Models in Geomechanics NUMOG 10 - Numerical Models in Geomechanics NUMOG 10 85 - 91 2007
Publishing type：Research paper (international conference proceedings)
A simple method for describing the stress-induced anisotropy of soils, which obey isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress tij, by which the influence of the intermediate principal stress on the deformation and the strength of soils is properly considered, has been proposed before. In the present study, this concept is extended and a new stress measure t*ij is incorporated to be able to consider the fabric change of soils due to variation of stress histories, namely, induced anisotropy. The evolution rule of t*ij is provided referring to the existing experimental evidence. Then, the modified stress t*ij is applied to an isotropic hardening elastoplastic model named Subloading tij model as an example. The model is verified by experimental results in isotropic and anisotropic compression and shear tests with different stress histories under triaxial conditions. © 2007 Taylor & Francis Group.
-
A simple modeling of structured soils Reviewed
T. Nakai, F. Zhang, H. Kyokawa, M. Kikumoto
NEW FRONTIERS IN CHINESE AND JAPANESE GEOTECHNIQUES 435 - 447 2007
Language：English Publishing type：Research paper (international conference proceedings) Publisher：CHINA COMMUNICATIONS PRESS
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in general stress systems is presented. Based on an idea that structured soils can be made due to a kind of bonding effects between soil particles, a simple elastoplastic model is formulated by extending subloading t(ij) model (Nakai and Hinokio, 2004). Firstly, a new interpretation of subloading surface concept for describing the influence of density and/or confining pressure is shown. Secondly a method to take into consideration the effect of bonding on the soil behavior in constitutive modeling is developed. By introducing this method for considering bonding to the subloading t(ij) model, the stress-strain behavior of structured soils can be described. The validity of the proposed model is checked through numerical simulation of oedometer tests and undrained shear tests on structured clays. An interpretation for super/subloading surface concept to describe structured soil by Asaoka et al. (1998) is also given, and the similarities and differences between the present model and super/subloading surface model are also discussed in detail.
-
Isotropic hardening model for soils considering stress-induced anisotropy Reviewed
M. Kikumoto, H. Kyokawa, T. Nakai, F. Zhang, M. Hinokio
NEW FRONTIERS IN CHINESE AND JAPANESE GEOTECHNIQUES 278 - 289 2007
Language：English Publishing type：Research paper (international conference proceedings) Publisher：CHINA COMMUNICATIONS PRESS
A simple method for describing stress-induced anisotropy of soils, which obeys isotropic hardening rule in modified stress space, is proposed. In present study, a modified stress t(ij), by which influence of intermediate principal stress on deformation and strength characteristics of soils is suitably taken into account, is extended to a new stress tensor t(ij)(*) to be able to consider inclusively the fabric change of soils due to the variation of the intermediate principal stress and the stress histories, namely, stress-induced anisotropy. The evolution rule of t(ij)(*) is provided referring to the past experimental and numerical evidences. In this paper, the modified stress t(ij)(*) is applied to an isotropic hardening elastoplastic model named subloading t(ij) model as an example. The proposed model is verified by results of true triaxial tests.
-
Extension of subloading t<inf>ij</inf> model to structured soils Reviewed
M. Kikumoto, T. Nakai, F. Zhang, M. Hinokio, A. Yagyu, H. Kyokawa
Proceedings of the International Symposium on Geomechanics and Geotechnics of Particulate Media - Geomechanics and Geotechnics of Particulate Media 305 - 311 2006
Publishing type：Research paper (international conference proceedings)
An elastoplastic constitutive model for clay and sand is proposed, which can describe not only the typical behaviors of normally and over consolidated soils under general stress conditions, but also the behaviors of structured soils that can be found in natural deposited ground. In order to describe the behaviors of structured soils, the superloading surface concept originally proposed by Asaoka et al. (1998) is introduced. In the present model, the structured state of soil is simply defined as the difference of void ratio between the structured and the completely remolded soil under the same stress conditions. The proposed model is verified by oedometer tests on manmade structured soils. Moreover, the characteristics of the proposed model are investigated theoretically for drained and undrained triaxial tests. © 2006 Taylor & Francis Group.
PREV - NEXT 