Award type：Honored in official journal of a scientific society, scientific journal 

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Language：English   Publishing type：Research paper (scientific journal)  

Seepage surface position of fill slope can fluctuate owing to rainfall and groundwater supply from behind the slope. Therefore, in this study, shaking-table tests of an unsaturated fill slope were conducted to examine the influence of the seepage surface position on the fill slope stability by comparing with previous results in the fully saturated condition. An acceleration amplification factor was used to evaluate the stability. If the embankment was in an unsaturated condition, a slip plane was formed along the seepage surface. With ongoing increase of input acceleration, the slip progressed to behind the slope. Comparison of the unsaturated and saturated results showed that although the failure mechanism in which the slip surface was formed by the reduction in rigidity was common, the input acceleration at failure and deformation mode were different. When the slip surface was formed and failure occurred, the input acceleration in the unsaturated fill slope was more massive, and the deformation at the same excitation stage was small. These results imply that the unsaturated fill slope has a higher earthquake resistance than the saturated fill slope. Moreover, it is shown that the progress of plastic deformation inside the embankment and the formation process of the slip plane can be estimated from the change in the acceleration amplification factor regardless of seepage surface position.

DOI： 10.21660/2020.78.j2036

Web of Science

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi:10.3390/app112311152

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In the 2011 Earthquake off the Pacific coast of Tohoku, extensive liquefaction occurred in the Kanto region. This resulted in the settlement and inclination of thousands of utility poles. In urban areas, utility poles are often installed in narrow easements with limited clearance. Therefore, a simple and inexpensive countermeasure is desired. In this study, we attempted to reduce the settlement and inclination of utility poles in the liquefied ground by providing drain
holes in the utility pole. In the centrifugal model tests conducted using pole models with drain holes at the bottom and sides, settlement and inclination decreased in relation to the amount of drainage. Therefore, it was determined that the drainage method has a definite effect on the reduction of both settlement and inclination of utility poles in the
liquefied ground.

DOI： https://doi.org/10.3208/jgs.15.643

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1139/cgj-2020-0419

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)  

all over the world. If the existing small-scale structures such as houses are tilted due to liquefaction, they suffer more serious damage than they are subsided. In this paper, the effect of countermeasure against tilting damage due to liquefaction using floating grid-type improvement was investigated by 2D model tests under 1g condition using eccentric model structure, and non-linear FEM analyses. From the results, it was found that the floating grid-type improvement can significantly suppress the settlement damage of structure by suppressing the lateral flow of the liquefied ground even if the dead load of structure is eccentric. It was also found that lateral flow of the liquefied soil hardly occurs when the structure inclines due to liquefaction, and the effect of countermeasure against tilting damage due to liquefaction using floating grid-type improvement was not as high as the effect of suppressing subsidence damage. Therefore, it was found that desirable to use a floating grid-type improvement and drainage method to prevent tilting damage of structure.

DOI： https://doi.org/10.2208/jscejam.76.2_I_279

Language：Japanese   Publishing type：Research paper (scientific journal)  

近年，多発している大規模な地震に伴う液状化によって多くの戸建住宅で深刻な被害が発生している．ここで，液状化被害の中でも構造物が傾斜する場合には構造物自体にも重大な損傷が発生するため，構造物が沈下する場合より被害はさらに深刻になる．そこで，本稿では接地圧が偏心し，傾斜被害が発生しやすい模型構造物を対象にした重力場での二次元模型実験や水～土骨格連成有限変形解析から浮き型格子状地盤改良による液状化被害の抑制効果について検討した．検討の結果，側方流動を抑制することを目的とした浮き型格子状地盤改良により，偏心荷重が作用した構造物においても液状化時における沈下被害を大きく抑制可能であることが分かった．一方で，浮き型格子状地盤改良で得られる傾斜被害抑制効果は沈下被害抑制効果ほど大きくないことが確認された．

DOI： https://doi.org/10.2208/jscejam.75.2_I_401

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.21660/2020.66.07893

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.21660/2020.65.4729

Web of Science

DOI： 10.1007/978-981-15-2184-3_61

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.21660/2019.57.4722

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)  

近年，多発している大規模な地震に伴う液状化によって多くの戸建住宅で深刻な被害が発生している．ここで，液状化被害の中でも構造物が傾斜する場合には構造物自体にも重大な損傷が発生するため，構造物が沈下する場合より被害はさらに深刻になる．そこで，本稿では接地圧が偏心し，傾斜被害が発生しやすい模型構造物を対象にした重力場での二次元模型実験や水～土骨格連成有限変形解析から浮き型格子状地盤改良による液状化被害の抑制効果について検討した．検討の結果，側方流動を抑制することを目的とした浮き型格子状地盤改良により，偏心荷重が作用した構造物においても液状化時における沈下被害を大きく抑制可能であることが分かった．一方で，浮き型格子状地盤改良で得られる傾斜被害抑制効果は沈下被害抑制効果ほど大きくないことが確認された．

DOI： https://doi.org/10.2208/jscejam.75.2_I_329

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1139/cgj-2017-0385

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.21660/2018.51.02150

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1139/cgj-2016-0019

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

While a temporary structure is relatively simple to erect and remove, the fact that no particular measures such as pile installations or soil improvements are taken for its protection can mean that there is a risk of it collapsing in the event of an earthquake. This paper reports a numerical analysis of the seismic stability of a temporary structure erected on a foundation of alternating clay and sand layers in a case where the surface layer is sandy and clayey. It finds that the main cause for the structure's collapse lies in 1) the increase in the amplitude of the tremors resulting from a coincidence of the predominant ground wave motion with the specific vibration of the structure, and 2) the decline in the bearing force and the consequent unevenness in the settlement of the structure as a result of liquefaction in the surface sand layer. One important prevention measure is to ensure that the specific vibration does not coincide with the predominant ground motion by making appropriate changes in the height and width of the structure; but another cheap but effective safeguard is to increase the area of contact between the structure and its foundation by laying a base immediately below the temporary structure.

Language：English   Publishing type：Research paper (scientific journal)  

The seismic resistance of a coastal artificial ground situated within the Port of Nagoya against the Tokai-Tonankai-Nankai triple-segment earthquake was assessed. The analysis was carried out using the elasto-plastic constitutive equation for soils (SYS-Cam clay model) mounted on the soil-water coupled finite element deformation analysis program The model focuses attention on the action of the soil skeleton structure, and the analysis allows description of the mechanical behavior of a wide range of soils without distinguishing between static and dynamic behavior. When considering earthquake damage, attention usually tends to focus only on the phenomenon of liquefaction in sandy grounds. In this paper, finite element analysis was employed to simulate the phenomenon of liquefaction of soft sand and, in addition, to show that because of disturbance of the soil during the earthquake, there is a danger of large settlement occurring over a long period after the earthquake in the soft clay layer directly beneath the area that is under the action of vertical loads.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In recent years, damage to embankments from earthquakes has been frequently reported. In this paper, the deformation and failure behavior of an embankment constructed on a weak clay foundation during and after an earthquake is investigated using numerical analysis, GEOASIA, assuming a 40 g centrifugal field. The main conclusions obtained were as follows. 1) Although the embankment remained stable without large deformation during the earthquake, a slip plane subsequently penetrated through the embankment, resulting in delayed failure (circular arc slip). 2) The deformation behavior (failure mode) of the foundation and embankment varies greatly depending on the characteristics of the incident seismic motions.

Language：English   Publishing type：Research paper (scientific journal)  

Compared with natural grounds formed by sedimentation over many years, reclaimed artificial grounds are often weak. In this work, modeling of a reclaimed offshore artificial ground and its seismic response analysis were carried out, and the vulnerability of the weak reclaimed layers to seismic activity is pointed out. This study was carried out using a soil-water coupled finite deformation analysis program GEOASIA incorporating an elasto-plastic constitutive model (the SYS Cam-clay model). This model is capable of describing, within a single framework, the behaviors of sands, clays, and intermediate soils consisting of sand/clay mixtures through their soil skeleton structures (structure, overconsolidation, anisotropy) and its works. In reclaimed sand, lateral flow and upward lifting of lightweight underground structures occur because of liquefaction during an earthquake. In reclaimed clay, long-term settlement, which continues for several years after the earthquake, occurs.

Authorship：Lead author   Language：English  

For a temporary structure, which is comparatively easy to placement and withdrawal, special countermeasures such as pile penetration or ground improvement are not taken into considerations. As a consequence, when an earthquake occurs during the placement/construction, personal injury might be caused by overturning of the temporary structure. In this paper, co- and post-seismic responses of interactive systems consisting of a temporary structure - alternately layered sandy/clayey foundations were numerically investigated by using a soil-water coupled elasto-plastic finite deformation analysis. The findings are mainly as follows. 1) An unstable structure such as temporary structure become at high risk of overturning by means of liquefaction of sand layer. 2) Although it is possible to consider countermeasure against overturning by widen the breadth and lower the height of the temporary structure, it turned out that installation of a construction board is very effective.

Authorship：Lead author   Language：English  

Naturally deposited sands/clays are mostly found in structured states. In addition, these are usually in overconsolidated states. Furthermore, they exhibit more or less a condition of anisotropy. In order to describe the mechanical behavior of these natural soils, the authors proposed an elasto-plastic constitutive model, namely Super/subloading yield surface Cam-clay model (E.g. Asaoka et al., 2002), in which three mechanical concepts and their evolution rules were introduced into the Cam-clay model; the first one describes `degradation of soil structure' due to ongoing plastic deformation, the second, `loss of overconsolidation', and the third, `development/loss of anisotropy'. It can be emphasized in the model that, for sand, the degradation of structure proceeds more rapidly than the loss of overconsolidation, while for clay, the loss of overconsolidation proceeds more rapidly than the degradation of soil structure. Thus, the model can describe sand and clay consistently within the same theoretical framework.
For evolution rule of soil structure, most simple one is to consider only the degradation process. But through the exhaustive observation of repeated undrained shear behavior of sand, especially pre and post cyclic mobility behavior, upgradation process of the soil structure can be truly found. So, in the present paper, the process of re-upgradeation for the soil structure due to the plastic volume expansion, i.e. the (positive) dilation, is newly introduced to the model, dividing the contribution of plastic deformation to the change of soil structure into the volumetric and deviatoric part as a sophisticated evolution rule for the soil skeleton structure. And, the importance of upgradation concept of soil skeleton structure can be showned in shear behavior of both sand and clay demonstrating their model responses
1) Sand: Cyclic mobility behavior can be described. Fig.1 shows the calculated result of repeated undrained shear behavior of medium dens

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English  

By using a soil-water coupled finite element method, deformation/failure behavior during and after the occurrence of an earthquake in a clay foundation-embankment system was numerically examined. The elasto-plastic constitutive model for the soil skeleton is the Super/subloading Yield Surface Cam-clay model. The embankment was calculated as a saturated soil. The results showed that the embankment maintained stability without any significant large deformation during the earthquake, while slip failure penetrating to the crest was suddenly generated a few hours after the earthquake.

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Authorship：Lead author   Language：English  

Language：English  

Huge volume compression of loose sand can be easily observed not under monotonic loading but under repeated shear stress application with small amplitudes, which is called compaction of sand. Although it takes long time the similar phenomenon is commonly observed even in highly structured natural clay, which has been called, for long years, secondary consolidation/delayed compression of natural clay. This study describes that these large-scaled volume compression observed both in clay and sand is due to the decay/collapse of soil skeleton structure that occurs with on going plastic shear deformation. Distinguishing the mechanical difference between sand and clay, the super/subloading elasto-plastic constitutive model still explains the mechanism of the volume compression of soils consistently.

Authorship：Lead author   Language：English  

To improve the construction surplus soil and to use the soil as a geomaterial, a densification technology of soil with high water con-tent such as dewatered sludge is studied. The densification is brought by the change from the `consolidation material' like clay to the `compactable material' like sand. The soil is crushed with air to an assembly of clay pebbles, the water content of which is ease to de-crease, and therefore the assembly can be compacted to high density without long consolidation time. The soil became low com-pressible and had high shear resistance, which can be describe by Super/subloading Yield Surface model.

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Highly structured naturally deposited clay exhibits the softening with plastic compression due to the decay of soil structure. The softening behavior can be expressed by Super/subloading Yield Surface Cam-clay model, SYS Cam-clay model (Asaoka et al., 2002), in which the concepts of “structure," overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. In the present study, in order to examine the effects on the softening behavior, the consolidation test with some constant stress ratios controlled by the strain rate was carried out using Joban clay, highly structured clay, and calculated by SYS Cam-clay model. The new findings are as follows. (1) The large compression due to the softening with plastic compression occurs when the stress ratio of consolidation was large, initial degree of structure was large and degradation speed of structure is rapid through the calculation. (2) The experimental results showed the same tendency as the calculation results. (3) The axial strain proceeded by 4% keeping the deviator stress q and mean effective stress p constant axial strain in the consolidation test with stress ratio of 1.3.

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

In the present study, undrained triaxial compression tests and oedometer tests were carried out on two types of naturally deposited undisturbed clay, Pleistocene clay and Holocene clay, and the behaviors of these clays were then simulated using the Super/subloading Yield Surface Cam-clay model (Asaoka, Nakano and Noda, 1998, 2000 and Asaoka et al., 2002), in which the concepts of “structure," overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. The findings of the present study are as follows:
1) For the two types of undisturbed clay, the Super/subloading Yield Surface Cam-clay model can simulate undrained triaxial compression behaviors ranging from the normally consolidated state to the overconsolidated state, corresponding to various isotropic pressures using a single set of material constants.
2) In addition, the model can simulate one-dimensional compression behaviors using the same material constants as those used for the undrained triaxial compression behavior simulation.
3) Both undrained shear and one-dimensional compression behaviors for the two types of undisturbed clay, that is Pleistocene clay and Holocene clay, which have different loading histories and have undergone different ageing effects, were simulated using the Super/subloading Yield Surface Cam-clay model by changing the evolution parameters.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Large amount of Tertiary mudstones appears by the major construction works, and the efficient use of mudstone is expected. But it is well known that Tertiary mudstone exhibits “slaking." In order to use mudstone with advantage, it is necessary to understand the effect of the slaking on mechanical behavior. Tertiary mudstones are used in assembly of crushed mudstone pebbles on using for construction. So, one-dimensional compression tests are carried out for the assembly of two types of Tertiary mudstones having a different resistance to slaking. And then these one-dimensional compression properties are simulated by the SYS Cam-clay model. The findings are as follows. (1) The stress state of the mudstone pebbles with a low resistance to slaking can be existed below the normal consolidation line (NCL) of the remolded mudstone under loading in e-σv space, while the mudstone pebbles with a high resistance to slaking can be existed above the NCL. (2) Through the model, the mudstone assembly with a low resistance to slaking can be regarded as sand, of which structure collapses quickly and overconsolidation loses slowly, while the mudstone assembly with a high resistance to slaking can be regarded as clay, of which structure decays slowly and overconsolidation loses quickly.

Authorship：Lead author   Language：English  

Language：Japanese   Publishing type：Research paper (scientific journal)  

To examine the effect of the initial soil structure on slaking susceptibility of Tertiary mudstone, one-dimensional compression tests are carried out for three kinds of tertiary mudstone with a different resistance to slaking. These one-dimensional compression properties are simulated by the modified Cam-clay model with Super/subloading yield surface and rotational hardening. The new findings are as follows. (1) The initial stress state of the mudstone with a high resistance to slaking in e-σv space is above the normal consolidation line (NCL) of the clay that was remolded from the mudstone, while the state of the mudstone with a low resistance to slaking is below the NCL. (2) From the model, the mudstone with a high resistance to slaking can be regarded as the high structured and overconsolidated clay, while the mudstone with a low resistance to slaking can be regarded as the heavily overconsolidated and less structured clay.

Language：English  

Language：English  

Language：English  

Authorship：Lead author  

Event date： 2023.11

Event date： 2023.9

Event date： 2023.8

Language：English  

Country：Kazakhstan  

Event date： 2023.7

Event date： 2023.5 - 2023.6

Language：Japanese   Presentation type：Oral presentation (keynote)  

Venue：つくば国際会議場  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.7 - 2022.8

Language：English   Presentation type：Oral presentation (invited, special)  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.3

Event date： 2021.12

Event date： 2021.9

Event date： 2021.9

Event date： 2021.9

Event date： 2021.8

Event date： 2021.7

Event date： 2021.7

Event date： 2021.5 - 2021.6

Presentation type：Oral presentation (general)  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Country：Japan  

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Country：Japan