Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from international society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from international society, conference, symposium, etc.  Country：United States

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Soils and Foundations  

Dynamic soil-water coupling analyses, based on the u-p formulation, are inapplicable to highly permeable soils, causing numerical instability. In this study, it is demonstrated that theoretical solutions to the u-p formulation itself certainly exhibit unconditional convergence regardless of the permeability coefficient. This suggests that the instability is only numerical and can be observed in a temporally discretized system. Firstly, the linearized governing equation for the u-p formulation was proven to be reduced to a damped wave equation under a one-dimensional condition, similar to the Full formulation. Secondly, theoretical solutions for the u-p formulation were derived and their unconditional convergence was confirmed. Then, the essential characteristics of the u-p theoretical solutions, that is, the underestimation of permeability, overestimation of compression wave celerity, and occurrence of negative pore water pressure against positive load application, were described and compared with theoretical solutions for the Full formulation.

DOI： 10.1016/j.sandf.2023.101421

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Earthquake Spectra  

The 2011 off the Pacific Coast of Tohoku earthquake caused extensive liquefaction damage to reclaimed land along the Tokyo Bay coast, even though it was approximately 400 km from the epicenter. The characteristics of the liquefaction damage include the fact that liquefaction occurred in soils with a high percentage of fine particles and that the distribution of liquefied and nonliquefied areas was nonuniform. The factors contributing to such nonuniform liquefaction damage included the heterogeneity of the ground materials and their depositional conditions, and the effects of the long earthquake duration. Although these points are certainly valid as reasons for the occurrence of severe liquefaction damage, they do not fully explain the mechanisms of the liquefaction of the fine-grained soils, or the localized extent of the liquefaction. To elucidate the severe and nonuniform damage, seismic response analyses of a multi-layered ground were conducted focusing on the stratigraphic irregularities in the ground beneath Urayasu city. The results showed that the thicker and softer sedimentary layers amplify the slightly long-period component of the seismic motion and increase the shaking at the ground surface. Moreover, the wave propagation in the ground became very complicated owing to the focal effect caused by the refractions and reflections of body waves at the stratum boundary, surface wave excitation at the base of the slope, and amplified interference between body and surface waves. This complex wave propagation contributed to nonuniform surface ground shaking and severe liquefaction damage. In addition, surface waves, which consist primarily of slightly long-period components, can propagate far and wide; as such, they triggered extensive damage owing to delayed shaking phenomena that continue even after the earthquake. The analysis results suggested that multidimensional elasto-plastic seismic response analyses considering stratigraphic irregularities are important for detailed seismic evaluation.

DOI： 10.1177/87552930231220005

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Soils and Foundations  

This study investigated sand anisotropy experimentally using a hollow cylinder apparatus. The effect of the initial anisotropy on the shear behavior of sand was illustrated by conducting experiments on specimens with bedding planes and systematically varying the density, principal stress direction, and intermediate principal stress. The change in induced anisotropy during shearing was experimentally captured by re-shearing the specimens subjected to prior shear history. The experimental results revealed the following: (a) Anisotropy in sand, whether initial anisotropy developing during specimen preparation or induced anisotropy developing due to shear history, causes pseudo-density changes in the mechanical behavior, in which sand of the same density behaves as if it has a different density depending on the direction of shear. (b) The changes in induced anisotropy, due to shearing in the same direction as that of the prior shear, make the soil behave similarly to dense sand, whereas shearing in a direction perpendicular to the prior shear makes the soil behave similarly to loose sand. (c) The larger the prior shear, the more pronounced the pseudo-density changes that appear in the subsequent behavior. Moreover, the significance of induced anisotropy in liquefaction and compaction phenomena was experimentally demonstrated through single and double swing cyclic shear tests. The results obtained from the study will be useful for validating models that incorporate induced anisotropy.

DOI： 10.1016/j.sandf.2023.101326

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

Elastoplastic constitutive equations for soils often employ the nonlinear rate-type isotropic Hooke’s law, which is based on theadditive decomposition of strain rate and considers the pressure dependency in the elastic part. Hooke’s law has independent isotropic anddeviatoric components, and therefore, it cannot express elastic dilatancy as confirmed in experiments. In this model, although the elastic vol-ume change is path-independent, the shear strain exhibits a significant residual when subjected to an effective stress cycle. This study pro-poses a rate-type elastic constitutive equation for soil applicable to elastoplastic constitutive equations based onfinite deformation theoryusing an objective stress rate and additive decomposition of stretching; these equations cover these shortcomings of the rate-type Hooke’slaw. The proposed rate-type elasticity constitutive equation is based on the hyperelastic body in the infinitesimal deformation theory proposedby Einav and Puzrin or Houlsby et al. and has confining pressure dependence, path independence of elastic volume change, and elastic di-latancy. Further, the residual strain is considerably smaller than that of the rate-type Hooke’s law. Moreover, this study improves the elasto-plastic constitutive equation, SYS Cam-Clay model, based on the skeleton structure concept by introducing the proposed elastic constitutiveequation. The basic behavior of the elastoplastic constitutive equation for clay and sand is demonstrated to show that the newly acquiredelastic dilatancy improves the mean effective stress reduction behavior during shear stress unloading under undrained conditions and thestiffness recovery behavior during liquefaction, which is essential for describing cyclic mobility.

DOI： 10.1061/IJGNAI.GMENG-7117

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

When simulating the vertical drain method using a soil–water coupled finite-element analysis, we the macroelement method can be adopted to provide the water absorption function of drains to individual elements approximately. A previous study added the discharge function of vertical drains to the technique so that the occurrence of well resistance can be considered in accordance with its mechanism. This paper verified the approximation accuracy of this new macroelement method in quasi-static problems. The macroelement method was derived under the assumption that the axisymmetric pore water pressure distribution is equal Barron’s solution, but the first numerical example demonstrated that the technique has high approximation accuracy even for nonaxisymmetric problems by appropriately converting the permeability of a drain. The second calculation example included a number of drains and applied the vacuum consolidation method to clayey ground containing a middle sand layer. In this calculation, there was remarkable well resistance, and pore water flowed from the unimproved region to the improved region or between the effective areas of each drain. The calculation results indicated the superiority of the new macroelement method in terms of accurate approximations even for such a complex problem. Moreover, this study demonstrated the effectiveness of waterproof sealing, a countermeasure for sucking pore water from the middle sand layer, using the new macroelement method.

DOI： 10.1061/(ASCE)GT.1943-5606.0002803

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

This study proposes a new method to introduce the cementation effect into existing elastoplastic constitutive models for soils. The mechanical properties of cement-treated soil are evaluated via element tests and compared with those of naturally deposited clay. The similarities and differences between cement-treated soils and naturally deposited clays are studied, focusing on two states, the undisturbed and remolded states. The effective stress for cement-treated soils incorporating an internal state variable representing the cementation effect is newly defined to describe the mechanical properties of cement-treated soils. Moreover, by applying this extended effective stress to the super-subloading yield surface (SYS) Cam-clay model, which is an elastoplastic model for soils based on the skeleton structure concept, the scope of this constitutive model is extended to include cement-treated soils. The cementation effect introduced by the proposed method allows reproducing the mechanical behavior of the cement-treated soil. Finally, a brittle behavior not described at the element level can be obtained, leading to a soil–water coupled finite deformation analysis incorporating the proposed constitutive model.

DOI： https://doi.org/10.1061/(ASCE)GT.1943-5606.0002727

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

It is desirable for spherical gas holders, which require a high level of safety, to be able to retain their functions during aftershocks even when the foundation is subjected to unequal settlement due to a largescale earthquake. For this purpose, it is necessary to develop a simple method to evaluate the seismic resistance of inclined gas holders under the assumption of maximum aftershocks, which will contribute to the decision on whether or not to use the holders after a large-scale earthquake. The analysis to evaluate each element of the holder must take into account the material and geometrical nonlinear response mechanism of the supporting structure and nonlinear dampers, and it is not realistic to conduct detailed evaluation by 3D analysis in a short period of time after an earthquake. Therefore, in this paper, the simple evaluation method using a single mass-spring analysis that reflects the nonlinear spring characteristics from the pushover analysis is proposed. This method shows good agreement with the dynamic response of a 3D framework model of an actual gas holder until the maximum response value, and after that, the response value is calculated on the safe side, which means that the aftershock seismic resistance of the holder can be evaluated.

DOI： https://doi.org/10.2208/jscejam.77.2_I_543

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Computers and Geotechnics  

This paper proposes a combined-loading elastoplastic constitutive model (CL model) for a unified description of the mechanical behavior of soil materials, including clay, sand, and intermediate soil. This mathematical model combines the super-subloading yield surface Cam-clay model and the non-associated Drucker–Prager (DP) model. The first model introduces the skeleton soil structure concept into the Cam-clay model based on critical-state soil mechanics. It describes the mechanical behavior of naturally deposited clay more accurately than the existing model does. The non-associated DP model considers the frictional properties of granular materials and is widely used to describe the undrained shear behavior, particularly that of sandy soil. The newly proposed model is one in which these two independently existing models simultaneously or independently work in loading states according to the loading criterion, which can be derived as a natural result from plastic multipliers. This framework allows for a unified description of a wide range of soil materials, including naturally deposited clayey soils and sandy soils.

DOI： 10.1016/j.compgeo.2021.104521

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Sciences (Switzerland)  

Safety measures are required for spherical gas holders to prevent them from malfunctioning even after a large earthquake. In this study, considering the strong nonlinearity of the ground and damage to the pile during an earthquake, a three-dimensional seismic response analysis of the holder-pile-ground interaction system was conducted for an actual gas holder on the soft ground consisting of alternating layers of sand and clay. In the analysis, the seismic response of the structure to strong ground motions of different durations with the same acceleration response spectrum was verified. The results show that the piles were relatively effective in controlling the settlement when the duration of the earthquake motion was long. This is because the axial force acting on the pile increased due to the redistribution of the holder load caused by the lowering of the effective confining pressure of the sand and clay layers during the earthquake, which increased the bearing capacity of the pile. In contrast, when the duration of the seismic motion was short, the piles had little effect on the reduction in the settlement because the maximum acceleration was higher than that in the former case, and the piles immediately lost their support function.

DOI： 10.3390/app112311152

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Scopus

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soils and Foundations  

The theoretical and numerical solutions for the one-dimensional dynamic deformation of saturated ground were obtained using the u–w–p governing equation. The numerical analysis was performed based on the finite element method, and the occurrence of superficially peculiar phenomena, i.e., S-shaped settlement–time relation, non-harmonic oscillation in the settlement/pressure–time relation in highly permeable soil, and inconsistency in the vertical load and immediate pressure was identified heuristically. The theoretical solution of the damped wave equation was derived from the original governing equation expressed as the superposition of several modes with different eigenvalues, and this solution could successfully explain the phenomena observed heuristically. It was noted that the phenomena were induced by the presence of inertia, because the static solution and u–p analysis did not exhibit such phenomena. The verification of the analysis was conducted owing to the correspondence of the theoretical solutions of the damped wave equation and the u–w–p analysis results.

DOI： 10.1016/j.sandf.2020.12.007

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Scopus

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

Considering unsaturated triaxial tests including a ceramic disk as initial and boundary value problems, a series of suction change, isotropic consolidation, and drained shearing processes was simulated using a soil-water-air coupled elastoplastic finite deformation analysis code. As a result, it was demonstrated that the delayed behavior of a wetting-induced collapse during the suction change and isotropic consolidation processes, as well as water-absorption behavior during the subsequent drained shearing process, were attributed not to the characteristics of the soil specimen, but to the permeability of the disk. Thus, it is important to take the ceramic disk into account in unsaturated triaxial tests regarded as initial and boundary value problems in order to understand the temporal change behavior of unsaturated soil specimens. Otherwise, there is a risk that the behavior appearing as the solution of an initial and boundary value problem may be modeled as a constitutive relation.

DOI： 10.1016/j.sandf.2020.12.009

Scopus

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

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：International Journal of GEOMATE  

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

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Scopus

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soils and Foundations  

Triaxial tests and numerical simulations were conducted to determine the water absorption compression of unsaturated soil. In the triaxial tests, unsaturated silt specimens under the same initial condition were prepared and the processes of different suction reduction, isotropic consolidation, and exhausted-drained shearing were applied to the specimens. The numerical simulations used a soil-water-air coupled finite deformation analysis code with a newly incorporated elastoplastic constitutive model. The degree of saturation was introduced to the internal state variables of the yield function of the SYS Cam-clay model and a soil-water characteristic model with void ratio dependency. Then, the triaxial test was treated as an initial and boundary value problem, and the series of processes in the experiments were simulated using a single set of material constants and initial values. The new findings are as follows:
1)The loading criterion and the classification of loading conditions considering change in saturation degree can be specified in the elastoplastic constitutive model for unsaturated soil.
2)Water absorption compression behavior was observed in the experiments not only under suction reduction but also under constant suction condition. This water absorption compression under constant suction condition was explained as a saturation-increase behavior due to volume compression using the soil-water characteristic model with void ratio dependency.
3)By considering the triaxial test as an initial and boundary value problem, the temporal change in the volume and the amount of water absorption/drainage were able to be reproduced.

DOI： 10.1016/j.sandf.2020.06.010

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Association for Earthquake Engineering  

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Association for Earthquake Engineering  

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Association for Earthquake Engineering  

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)  

Due to heavy rain in northern Kyushu in July 2012, failure of the Yabe River levee occurred, caused by local piping in highly permeable foundation ground, and it was a great shock when river engineers and researchers realized that levees can collapse without overflow. Regarding the Koyoshi River levee slope slip and the Kakehashi River levee slope failure that occurred in July 2013, it is also considered that the damage was the result of highly permeable foundation ground. In this paper, to clarify the seepage failure mechanism of river levee with highly permeable foundation ground, numerical simulations of model tests were conducted using a soil-water-air coupled finite deformation analysis code. As a result, the simulation was able to reproduce the difference between the case when the seepage failure occurred and the case when the seepage failure did not occur in the experiment. In addition, using this analysis code, case studies were conducted and the influence of introducing suction effect to elastoplastic constitutive model on seepage failure behavior was also discussed.

DOI： 10.2208/jscejam.75.2_I_379

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

Earthquake resistance of important structure have been promoted based on the lessons learned from the big Earthquake in Japan. However, liquefaction still causes serious damages to many detached houses in the world. Also, most soil improvement methods apply to original ground without structure, and countermeasure against liquefaction for existing small structure has not been sufficiently investigated. Therefore, we investigated reduction effects of liquefaction damage using small grid-type improvement as countermeasure against liquefaction for existing small structure. To this end, 2D model tests under 1g condition and non-linear FEM analyses have been carried out. From the model tests results, it was found that if the interval of improved wall is within 1.2 times of the base width, some degree of counter measure effect agaisnrt subsidence due to liquefaction can be obtained with a small grid-type improvement where the improvement depth is about twice the base width. The numerical simulation has shown a similar result as found in the observations.

DOI： 10.2208/jscejam.75.2_I_329

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

In the 2011 off the Pacific Coast of Tohoku Earthquake, the liquefaction damage in the residential area of Urayasu City was huge, and many detached houses suffered uneven settlement. In Japan, however, there has not been sufficient knowledge about liquefaction- induced damage of detached houses. Therefore, in this study, with regard to the liquefaction damage form of the detached houses constructed on the liquefiable ground, the following points were clarified focusing on the influence of the neighboring houses using soilwater coupled finite deformation analysis. 1) In the case of single structure evaluation, even if stability is maintained without tilting, tilting damage may occur when considering neighboring houses. 2) The direction of inclination of neighboring houses can be explained by using the computed direction of post-seismic displacement vector in the case of one house alone.

DOI： 10.2208/jscejam.75.2_I_401

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

The earthquake damage prediction is mainly focused on the seismic instability of sandy foundations although the clayey foundation could also be vulnerable to earthquake damage. Moreover, it is known that clayey soil shows a marked loading rate dependency in monotonic shear behavior due to its low permeability. Therefore, this paper aims to determine the undrained cyclic shear behavior of clayey soil under a drastically changed loading rate. Reconstituted clayey samples were subjected to undrained cyclic triaxial compression/extension tests with loading rate from 1.0Hz to 0.0042Hz by stress control, and 0.01%/min by strain control. The cyclic loading was stopped when the double amplitude exceeded 5%. Then, the specimen was left for a while in an undrained condition, until the value of pore water pressure converged. Results revealed that as the loading rate decreases, the number of cycles that corresponds to DA=2% and 5% also decreased. Therefore, the degree of strain evolution varies depending on the loading rate and the undrained shear strength also varies depending on the cyclic loading rate. This is because when the cyclic loading rate was high; the pore water did not migrate sufficiently, leading to the non-uniform distribution of the excess pore water pressure inside the specimen. However, the final values of excess pore water pressure after the homogenization process was the same regardless of the loading rate. This means that if sufficient time is left after cyclic loading, the final mean effective stress value becomes equal regardless of the loading rate.

DOI： 10.21660/2020.66.07893

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Scopus

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

DOI： 10.21660/2020.65.4729

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Scopus

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

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Canadian Geotechnical Journal  

Replace Fig. 10 with the figure shown herein, where labels “(a)” and “(b)” have been added; and “ch.3 (upper)”, “ch.2 (middle)”, and “ch.1 (lower)” in part (b) of the figure have been replaced with “ch.6 (upper)”, “ch.5 (middle)”, and “ch.4 (lower)”, respectively.(Image presented).

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：16th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2019  

Displacements of strike-slip faults generate Riedel shear bands and flower structures at the surface ground above the faults. This paper aims to simulate deformation of strike-slip deformation of the surface ground considering jogs as geometrical imperfections. Analyses are based on the GEOASIA with SYS Cam-clay model that considers overconsolidation, which allows us to simulate softening behavior of brittle materials. Since the analytical results consider the presence of jogs, fractal shear zones (duplexes), P-shear, R/R'-shear, outer shear/splay shear, and tulip/palm-tree structures are successfully simulated. Furthermore, in terms of the scale effect, Riedel shear bands fractally appear when setting same overconsolidation ratio at the bottom of models.

Scopus

Language：English  

Displacements of strike-slip faults generate Riedel shear bands and flower structures at the surface ground above the faults. This paper aims to simulate deformation of strike-slip deformation of the surface ground considering jogs as geometrical imperfections. Analyses are based on the GEOASIA with SYS Cam-clay model that considers overconsolidation, which allows us to simulate softening behavior of brittle materials. Since the analytical results consider the presence of jogs, fractal shear zones (duplexes), P-shear, R/R'-shear, outer shear/splay shear, and tulip/palm-tree structures are successfully simulated. Furthermore, in terms of the scale effect, Riedel shear bands fractally appear when setting same overconsolidation ratio at the bottom of models.

Language：English  

A soil-water-air coupled finite deformation analysis of unsaturated silt triaxial tests, which were conducted by Kodaka et al. (2006), was performed considering the triaxial test not as an element test but as an initial and boundary value problem. The analysis can deal with suction effect accounting it in the elasto-plastic constitutive equation, SYS Cam-clay model. A series of processes of suction variation, isotropic consolidation, and exhausted-drained shearing were simulated beginning from a single initial condition and using a single set of material constants. The results showed that considering ceramic disc permeability was required to reproduce well both the mechanical and hydraulic behavior. Accordingly, it is suggested that a laboratory test result should be seized as the solution for an initial and boundary value problem. In addition, to experimentally clarify that the ceramic disc permeability is comparatively low, unsaturated silt triaxial tests were conducted using both a ceramic disc and a micro-porous membrane for suction control.

Authorship：Lead author   Language：English  

Extensive liquefaction damage was observed in the 2011 off the Pacific coast of Tohoku Earthquake over a wide range of reclaimed coastal land. It is reported that in Chiba Prefecture, the large aftershock that occurred 29 minutes after the main shock extended the liquefaction damage in sandy ground. In this paper, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation SYS Cam-clay model, it is shown that the groundwater level rises due to the main shock and that during the aftershock, this groundwater level rise could cause extended liquefaction damage.

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Soils and Foundations  

Most soil–water coupled analyses of saturated soil are based on the u–p formulation, where a set of equations is reduced by assuming that the acceleration of the fluid phase relative to that of the solid phase is less than that of the solid phase. Therefore, this analysis cannot be used for a coupled analysis with dynamic water flow in highly permeable soil. This study aims to present a soil–water coupled finite deformation analysis method based on full formulation, or u–w–p formulation. This method differs from conventional methods in the following ways: (1) the governing equations explicitly include the equation of motion for the fluid phase, (2) a relative convective term is used to describe a change in the relative configuration between the two phases, and (3) the moving/inclined discharge boundary is directly implemented to the discretized governing equations. Herein, one/two dimensional seepage and plane-strain deformation analysis results are reported. In the seepage analysis, accelerating permeation of pore water is obtained and the undrained constraint condition is verified. In the deformation analysis, dynamic migration in a high permeable soil specimen, i.e., wave propagation and rotational flow of pore water, is observed.

DOI： 10.1016/j.sandf.2019.03.008

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Scopus

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

In the vacuum consolidation method, the pressure under the air-tight sheet increases according to ground surface settlement. An air-water separation system for the vacuum consolidation method (VCM) was developed to improve this issue and enhance the vacuum effect. Although it has been demonstrated up to today that the system can obtain a higher vacuum pressure, the suppression effect of the new type VCM against deformation has never been discussed. In this study, therefore, mainly to reveal the suppression effect of the new method against deformation, several numerical simulations were conducted by using a soil-water coupled analysis code, GEOASIA, which mounts the macro-element method with discharge and drainage functions of vertical drains. The main findings of this study are as follows: 1) The air-water separation system has a high efficiency against deformation. Especially, the method remarkably restricts settlement that occurs after stopping vacuum pumps because it has a high preloading effect. 2) The conventional VCM also restricts deformations including a lateral deformation even if large settlement occurs. This is because the vacuum loading effect is maintained even though the pressure under the airtight sheet increases according to ground surface settlement. 3) Short-term constructions that have never been attempted can be performed in both the type VCMs. The above discussions demonstrated that the
numerical simulation method used in this study allows the selection of effective countermeasures and
economical construction conditions.

DOI： https://doi.org/10.2208/jscejge.75.303

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

The strain parameter-triggering liquefaction is usually determined by implementing cyclic strain approach with a corresponding laboratory experiment. These parameters are threshold shear strain, cyclic shear strain and cyclic shear strain that would trigger liquefaction. In this study, non-contact measurement technique was implemented to estimate and monitor the development of the mentioned parameters. In this technique, a mirrorless camera and Lucas and Kanade pyramidal optical flow algorithm were utilized to track the movement of the particles. The camera was first calibrated to eliminate the errors from the lens and the scene as well. Furthermore, curvature correction was applied because the sample tested has a curved profile. The comparison was made with the loose and medium dense conditions. The samples were tested under a consolidated undrained cyclic triaxial test at 2.4, 1.6 and 0.8 mm strain amplitudes. The confining pressures used were 50, 100 and 200 kPa. Based on the results, a non-contact measurement technique can estimate the parameters. A range of values was established due to the non-homogeneous movement of the soil.

DOI： 10.21660/2019.57.4722

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

DOI： 10.20965/jdr.2019.p0375

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Scopus

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

Due to heavy rain in northern Kyushu in July 2012, failure of the Yabe River levee occurred, caused by local piping in highly permeable foundation ground, and it was a great shock when river engineers and researchers realized that levees can collapse without overflow. Regarding the Koyoshi River levee slope slip and the Kakehashi River levee slope failure that occurred in July 2013, it is also considered that the damage was the result of highly permeable foundation ground. In this paper, to clarify the seepage failure mechanism of river levee with highly permeable foundation ground, numerical simulations of model tests
were conducted using a soil-water-air coupled finite deformation analysis code. As a result, the simulation
was able to reproduce the difference between the case when the seepage failure occurred and the case when the seepage failure did not occur in the experiment. In addition, using this analysis code, case studies were conducted and the influence of introducing suction effect to elastoplastic constitutive model on seepage failure behavior was also discussed.

DOI： https://doi.org/10.2208/jscejam.75.2_I_379

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

As a construction method that can be constructed in even narrow space to suppress both liquefaction and lateral defomation of the ground behind the quay, referring to the previous study which was con-firmed effectiveness, we proposed a method for arranging steel sheet-pile shear walls in the direction per-pendicular to the quay wall. By analyzing using a soil-water coupled finite deformation analysis code, GEOASIA, we confirmed that the proposed method was useful in terms of suppressing liquefaction and lateral defomation. Furthemore, we showed the effectiveness of a new countermeasure method by reveal-ing that the reinforcement effect was proportional to the distance between the sheet-piles and shape of steel sheet-pile. This is a result that can be derived by finite deformation analysis.

DOI： https://doi.org/10.2208/jscejam.74.I_615

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

This paper reports seismic response analyses about the spherical gas holder which requires higher safety focusing on the ultimate limit state of the level 2 earthquake. In the analysis, a gas holder and pile
foundation are modeled in 3D condition to evaluate their interactive behavior more realistically using a soil-water coupled finite deformation analysis code GEOASIA.
As a result, in the holder to be analyzed this time, all the piles lose the bearing function, and the piles have an insignificant effect on the response of the holder. Therefore, the ultimate limit state, which we have considered the maximum unequal settlement in the past examination, is assumed considerably safe. Also, under the greatest possible earthquake condition with this holder, it is possible to almost fully evaluate the seismic performance of the ultimate limit state by 2D analysis. On another front, 3D analysis should be applied for non-uniform condition such as a substandard earthquake input and irregular surface layers. Furthermore, by using this analysis method, it is possible to evaluate the structural stability of the
gas holder integrally.

DOI： https://doi.org/10.2208/jscejam.74.I_693

Language：English   Publishing type：Research paper (scientific journal)   Publisher：7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019  

Extensive liquefaction damage was observed in the 2011 off the Pacific coast of Tohoku Earthquake over a wide range of reclaimed coastal land. It is reported that in Chiba Prefecture, the large aftershock that occurred 29 minutes after the main shock extended the liquefaction damage in sandy ground. In this paper, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation SYS Cam-clay model, it is shown that the groundwater level rises due to the main shock and that during the aftershock, this groundwater level rise could cause extended liquefaction damage.

Scopus

Language：English  

Anisotropy refers to the directional dependence of material properties. In order to know the true behavior of naturally deposited soil, the knowledge of development/diminishing of anisotropy are very important. The anisotropy of clays and silty clay intimately connected with their structure, which depends on the environmental conditions during which the soil is deposited as well as the stress changes subsequent to deposition. In this paper, triaxial tests were carried out using the vertical and the horizontal extraction specimen of the reconstituted clay and silty clay, for accumulating experimental facts of development of anisotropy during the preliminary consolidation process and the influence of the anisotropy on the shear behavior. Pre-consolidation pressure of 200kPa applied to induced initial anisotropy. Undrained shear triaxial test was performed with different isotropic stresses on clay and silty clay, isotopically consolidated for 24 hours and undrained shearing was carried out under constant axial strain rate of 0.0056(mm/min). Vertical sample shows larger peak strength as compared to horizontal, because of the development of anisotropy on the compression side. As the confining pressure increases, the difference between peak strength of vertical and horizontal becomes smaller and smaller which indicate that the anisotropy diminished and intensity ratio decreases. By comparing clay and silty clay, silty clay materials lose their anisotropy at lower confining pressure as compared to clay materials. Therefore, the grain sizes have significant effect on the developing and diminishing of anisotropy. Another important fact observed was critical state index is decreasing and become constant as confining pressure increases.

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

本研究では，愛知県の巨大産業を支えるサプライチェーンを擁する地域のひとつである碧南市を対象として，南海トラフ巨大地震による地震動に対する堤体基礎の沈下量を数値解析によって評価した．この解析結果を津波氾濫解析に組み込むことで，堤体基礎の脆弱性が氾濫過程や浸水域に与える影響について検討を行った．堤体基礎の沈下や直立堤の崩壊を考慮することにより津波浸水域は大きく拡大することを定量的に示すことができた．このことは，沿岸構造物の耐震化の重要性を示していることはもちろんのこと，強震動による海岸・河岸構造物や堤体基礎部の脆弱性が津波ハザード評価に与える影響を無視できないことを示している．

DOI： 10.2208/kaigan.74.I_247

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

DOI： 10.1139/cgj-2017-0385

Web of Science

Scopus

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

In recent studies triggering or initiation of liquefaction is usually performed to characterize the potential of the soil to liquefy. Its behavior before, during and after liquefaction in a laboratory test needs to be understood. Image processing was implemented to monitor the triggering of liquefaction and estimate the cyclic shear strain that would trigger liquefaction. Lucas and Kanade pyramidal optical flow algorithm were used to track the movement of the soil. A mirrorless camera was the instrument used. The strain-controlled consolidated undrained cyclic triaxial test was performed. The loose condition was tested at 2.4, 1.6 and 0.8 mm strain amplitudes. The confining pressures used were 50, 100 and 200 kPa. Based on the results, the estimated values for the cyclic shear strain that would trigger liquefaction had a range of values due to the occurrence of non-homogeneous deformation. The minimum values were in agreement with the typical values while the maximum values were larger. For the behavior of the soil before, during and after liquefaction had occurred, the deformation behavior was different. More deformations were observed after the triggering of liquefaction.

DOI： 10.21660/2018.51.02150

Web of Science

Scopus

Language：English  

Language：English  

Cyclic threshold shear strain is the cyclic shear strain amplitude that serves as the indicator of the development of pore water pressure. The parameter can be obtained by performing either cyclic triaxial test, shaking table test, cyclic simple shear or resonant column. In a cyclic triaxial test, other researchers install measuring devices in close proximity of the soil to measure the parameter. This method can cause sample disturbance which can affect the result of the experiment. Although there are already existing methods for determining the parameter, the movement and behavior of the soil before and after reaching this parameter needs to be understood. A method that can be used is by applying full-field measurement technique. The technique uses a camera to monitor and measure the movement of the soil. This study is an attempt to estimate the cyclic threshold shear strain parameter. The applied technique has the capacity to monitor the behavior of the particles at cyclic loading. For this study, the technique was incorporated in a strain-controlled consolidated undrained cyclic triaxial test. Two-dimensional image processing was implemented. Lucas and Kanade optical flow algorithm were applied to track the movement of the soil particles. Results from the full-field measurement technique were compared with the results from the linear variable displacement transducer. A range of values were determined from the estimation. The minimum values were in the order of 10-2% in some areas of the specimen. Nonhomogeneous movement was also observed.

Language：English  

Deformation in a conventional cyclic triaxial test is normally measured by using a point-wise measuring device. In this study, non-contact measurement technique was applied to be able to monitor and measure the occurrence of the non-homogeneous behavior of the soil under cyclic loading. Non-contact measurement is executed through image processing. Two-dimensional measurements were performed using Lucas and Kanade optical flow algorithm and it was implemented Labview. In this technique, the non-homogeneous deformation was monitored using a mirrorless camera. A mirrorless camera was used because it is economical and it has the capacity to take pictures at a fast rate. The camera was first calibrated to remove the distortion brought about the lens and the testing environment as well. Calibration was divided into 2 phases. The first phase was the calibration of the camera parameters and distortion caused by the lens. The second phase was for eliminating the distortion brought about by the triaxial plexiglass. A correction factor was established during this phase. A series of consolidated undrained cyclic triaxial test was performed using a coarse soil. The results from the non-contact measurement technique were compared to the measured deformation from the linear variable displacement transducer. It was observed that deformation was higher in the area where failure occurs.

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

名古屋港ポートアイランド(以下，PI)には，名古屋港の機能維持のため，毎年多くの浚渫土が仮置きされている．地震によりPIの護岸が被害を受けると，浚渫土の流出等により，名古屋港の機能低下に直結する恐れがある．本研究では，PIを対象に南海トラフ巨大地震を想定した地震動を用い，地震応答解析を実施し，浚渫土砂埋立高さがPIの地震時の挙動に及ぼす影響を調べた．結果は以下の通りである．現状の埋立高さであれば，浚渫土が護岸を乗り越えて港湾へ流出するまでには至らない．しかし，現状から4mの嵩上げを行うと，護岸部の変状が大きくなり浚渫土が港湾へ流出する危険性が高くなる．一方，埋立天高さを下げることにより，埋立地盤や護岸の側方流動を軽減できる．つまり，PIの埋立高さを少しでも低くすることが，地震被害を低減する上で重要である．

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

地盤に長尺の杭が打設されている場合，地盤変位が大きく生じる大地震時には，杭の損傷が懸念される．これまでに，地盤の降伏および杭周面地盤の回り込みの影響を確認するために，土層内に配置された杭に強制変位を与える模型実験が実施され，杭に作用する地盤反力と粘性土のせん断強度の関係を把握している．本報では，模型実験のシミュレーションを行い，数値解析コードのValidationを行うとともに，自然堆積粘土地盤を想定した数値実験を実施した．その結果，1）間隙水のマイグレーションの影響で，地盤反力は，ある載荷速度領域内で急変すること，2）鋭敏比が大きく軟弱な自然堆積粘土地盤を想定した場合，再構成地盤に比べて地盤反力が小さくなるとともに，地盤内で局所的なせん断帯が次々と発生し，せん断ひずみの発生領域が広がることを示した．

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

DOI： https://doi.org/10.4307/jsee.66.2_64

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ISRM International Symposium 2000, IS 2000  

Delayed deformation and progressive failure of a cut slope in an overconsolidated clays is examined through a series of soil-water coupled finite deformation analysis using the subloading surface Cam-clay model for overconsolidated soils. In this present problem analyzed, the slope exhibits progressive failure after a long time period (90 years), associated with the fluctuation of nodal velocities on the slope. High shear strains occur initially at the toe of slope and subsequently propagate towards the top of slope with time forming a clear “circular slip surface”. The overconsolidation ratio (OCR) in this highly sheared zone is almost equal to 1.0 due to softening with swelling. Time to failure depends on the soil permeability that comes to the soil-water coupled analysis with Darcy's law. For either high initial OCR or low heights of the slope, no failure is observed due to lesser porewater migration within the slope that results low shear strain.

Scopus

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

Japan has a large number of reclaimed regions unimproved against liquefaction and countermeasures in such regions are necessary to prepare for a great earthquake. A new macro-element method has been proposed that involves applying the soil-water-coupled finite deformation analysis code GEOASIA with an inertial term, and a numerical-analysis technique has been designed that quantitatively evaluates the improvement effect of the pore water pressure dissipation method (PWPDM). In this study, PWPDM effectiveness was examined for a reclaimed ground using the proposed method. Detailed examinations were conducted with the intention of developing a more advanced performance design, without being limited to the concept of the current design code. The main findings are as follows: 1) the proposed analysis code enables quantitative evaluation of the improved effectiveness of PWPDM in a reclaimed ground; 2) more advanced PWPDM designs are possible by not only suppressing the maximum excess pore water pressure to the permissible range of the current design code, but also evaluating the ground deformation adequately; and 3) the new macro-element method, capable of reproducing the phenomenon of well resistance, can evaluate the reduction in the improvement effect because of the degradation of drainage capability, thus making it useful for maintenance purposes such as drain clogging.

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

Web of Science

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

DOI： 10.2208/jscejge.73.311

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

Conventional seismic assessments of river embankments have focused on liquefaction damage of sandy ground. However, following the 2011 earthquake centered off the Pacific Coast of Tohoku, extensive damage of river embankments built on a clayey foundation has garnered greater attention. This paper presents seismic response analyses of river embankments constructed on soft and sensitive estuarine clay, as well as analyses of countermeasures implemented with sheet piles with a succession of penetration depth and placement. River embankments have kept stable if the clayey ground was assumed to be a nonsensitive condition. However, if a strong shake impacts actual sensitive clay, there is a risk of slippage generated from the clayey layer. If the penetration depth of piles is shallow in the clayey layer, the clay is strongly disturbed by the tip of the pile, generating extensive damage; if the penetration depth is sufficiently deep in the supporting layer, significant deformation control may be obtained at the reinforced side, although there is a risk of promoting deformation at the opposite side. These results indicate the importance of the specific inspection of pile penetration depth; otherwise, not only is it not possible to obtain a sufficient countermeasure effect, but also an adverse effect may be generated.

DOI： 10.1139/cgj-2016-0019

Web of Science

Scopus

Language：English  

In the mechanics of saturated soil based on the theory of mixtures, the pore water pressure p and the displacements u and U of the solid and liquid phases, respectively, are assumed to be independent variables that are unknowns of the field when solving the equation of motion of each phase by coupling with the law of conservation of mass. This is called full formulation. In many analysis codes for saturated soil, this strict formulation is modified to reduce the number of equations by assuming that the
acceleration of the liquid phase relative to the solid phase is much smaller than that of the solid phase (u-p formulation). As this assumption neglects the dynamic permeation of pore water, it has not been possible to apply u-p formulation to soils with very high permeability. This paper demonstrates that by utilizing the finite element method, the finite volume method, etc., it is possible to carry out deformation analysis of soils with very high permeability by solving the strict governing equations based on full formulation for finite deformation fields of soil-water coupled systems.

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

In the simulation of the vertical drain method using a soil-water coupled finite element analysis, a macro-element method has often been used as an approximate method to introduce the water absorption functions of drains into individual elements. In order to extend the function of this method, the authors modified the formula of the flow coefficient from soil to drains and introduced the discharge function of vertical drains to the method by treating the water pressure in the drains as an unknown and adding a continuity equation for the drains to the governing equations. The first attempt made it possible to divide a finite element mesh independently of the drain arrangement and the drain spacing, and the second attempt enabled the well resistance to be automatically generated by a series of calculations depending on the given conditions. Furthermore, although the macro-element method has been applied to quasi-static problems in most cases, the authors applied the expanded one to dynamic problems by equipping it with the soil-water coupled finite deformation analysis code GEOASIA with the inertial term. In this paper, in order to verify the new macro-element method in a dynamic problem, the results of a 2D approximate model using the new macro-element method were compared with those of a 3D exact model where vertical drains were exactly represented by finely dividing the finite element mesh in the case of a sand ground improved by the pore water pressure dissipation method under the embankment. The findings of this study are as follows: (1) 2D mesh-based analyses under plane strain conditions, using the new macro-element method, can accurately approximate 3D mesh-based analyses with a fine mesh in dynamic problems in terms of changes in the excess pore water pressure and ground deformation; (2) the new macro-element method can adequately evaluate the influence of drain spacing on a countermeasure for liquefaction in the quantitative sense, while using a single mesh; and (3) the new macro-element method improves the calculation efficiency in the simulation of the pore water pressure dissipation method by laborsaving in mesh-dividing and dramatically reducing the calculation time.

DOI： 10.1016/j.sandf.2017.05.012

Web of Science

Scopus

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

The 2011 Great East Japan Earthquake caused massive ground damage, including liquefaction of sandy grounds, collapse of river levees and lands developed for housing, etc., particularly in regions across eastern Japan. Not only damage to 'currently unqualified' structures that did not conform to existing design standards and codes but also ground damage that could not be explained within the framework of conventional geomechanics and geotechnical engineering was observed. Particularly in the latter case, therefore, it has become necessary to develop new techniques in geomechanics without being restrained by the conventional framework. From the above standpoint, this paper reviews the research that has been carried out in the field of geotechnology after the Great East Japan Earthquake. More specifically, new knowledge relating to the mechanism of liquefaction damage at Urayasu City and other ground deformation caused by the earthquake is introduced, together with the results of research carried out on ground strengthening techniques.

DOI： 10.2208/journalofjsce.5.1_133

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

本論文では，液状化危険度の高い地盤上に実在する煙突を対象に，二次元平面ひずみ条件下での地震応答解析を実施し，地盤－構造物相互作用系における耐震性評価を行った．その結果，地震波が構造物の固有周期帯を多く含んでいると，共振によって構造物の揺れが大きくなることに加えて，液状化によって剛性を失った地盤が煙突を支えることができず傾倒してしまうことを示した．つまり，地盤の上に建つ構造物の地震時挙動は，加速度の大きさのみで評価できるのではなく，構造物の固有周期と入射される地震動の卓越周期との関係性が極めて重要であることを意味する．また，地盤の不整形性および周辺構造物の影響評価を行ったところ，深部地層の傾斜や周辺構造物による引きずり込み沈下によって，上部構造物の地震時安定性が低下することを示した．

DOI： http://doi.org/10.2208/jscejam.72.I_409

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

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ICSMGE 2017 - 19th International Conference on Soil Mechanics and Geotechnical Engineering  

In the mechanics of saturated soil based on the theory of mixtures, the pore water pressure p and the displacements u and U of the solid and liquid phases, respectively, are assumed to be independent variables that are unknowns of the field when solving the equation of motion of each phase by coupling with the law of conservation of mass. This is called full formulation. In many analysis codes for saturated soil, this strict formulation is modified to reduce the number of equations by assuming that the acceleration of the liquid phase relative to the solid phase is much smaller than that of the solid phase (u-p formulation). As this assumption neglects the dynamic permeation of pore water, it has not been possible to apply u-p formulation to soils with very high permeability. This paper demonstrates that by utilizing the finite element method, the finite volume method, etc., it is possible to carry out deformation analysis of soils with very high permeability by solving the strict governing equations based on full formulation for finite deformation fields of soil-water coupled systems.

Scopus

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

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

The reinforced earth wall have come into wide use in Japan after the Great Hanshin Earthquake in particular. Various types of reinforcing members are applied in that reinforced earth walls, e.g. metal strips, geosynthetics, steel bars with a bearing plate, and so on. Some of them have been developed in Japan. The authors have newly developed a reinforcing member incorporating both bearing resistance and friction resistance. In the present paper, a series of the small-scale pull-out test of the reinforcing members consisting of a steel bar with friction plate and bearing plate are performed to confirm the effectiveness of the reinforcement. From the test results, as to the cross-sectional shape of the friction plate, the friction plate of long shape in depth direction performed large pull-out resistance compared with the plate of short shape of the same sectional area. Enough resistance of the friction plate was demonstrated by setting it apart from a bearing plate in order to cut off the influence of the bearing plate. Furthermore, in the beginning of the pull-out, a ratio of contribution of the friction resistance to the bearing resistance was 60 to 70%. The contribution ratio of the friction resistance decreased to 40 to 50 % in a final stage of pull-out.

DOI： 10.3208/jgs.11.201

Language：English  

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

Numerous river levees on clayey soil grounds were damaged by the 2011 off the Pacific coast of Tohoku Earthquake. In order to investigate such damage, the behavior of an unsaturated embankment on clayey ground was simulated during its construction, during an earthquake and after the earthquake. The simulation was carried out using a soil-water-air coupled finite deformation analysis code, with attention being focused on the effect of groundwater level. The results indicated that if the groundwater level is high, a saturated area (settlement-induced saturation area) is formed at the base of the embankment due to penetrative settlement during/after construction. In addition, the mean skeleton stress is low compared with the low groundwater level. As a consequence, in the embankment on ground with the high groundwater level, the co-seismic deformation is greater and the mean skeleton stress decreases sharply, particularly in the settlement-induced saturation area during the earthquake. It was also shown that after the earthquake, the groundwater level rises because water flows toward the unsaturated embankment from the settlement-induced saturation area and/or the saturated clayey ground. If the groundwater level is high, in particular, a phreatic line is formed temporarily within the embankment.

DOI： 10.1016/j.soildyn.2016.02.008

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

The widespread liquefaction disaster that occurred in the reclaimed land around Tokyo bay area during the Great East Japan Earthquake was alarming. Validating this disaster by simulation is needed to prevent any liquefaction that may occur during likely huge future earthquakes. To this end, accurate soil properties and appropriate input wave as well as the finite deformation analysis that simulates the reappearance of liquefaction should be comprehended. In this study, soil-water coupled analysis code GEOASIA with SYS Cam-clay model, which can reproduce the function of soil structure, was used. Firstly, elasto-plastic properties of Urayasu soils were identified from the results of boring survey and laboratory testing. Then, by means of transfer method, both NS and EW upward waves at the foundation ground were simultaneously estimated from K-NET recorded motions at Urayasu.

DOI： 10.5610/jaee.16.4_155

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

A slip on the strike-slip fault causes flower structures and Riedel shear band within the overlying cover. This paper simulates the formation of these structures, employing the dynamic elasto-plastic finite defor-mation analysis code GEOASIA®.
The main conclusions are as follows: (1) A set of Riedel shear structures accompanies the plastic ex-pansion of the material, (2) A pattern of the initial material imperfections dominantly influence the for-mation process of Riedel shear structures and (3) Riedel shear bands don't appear in larger models, whose bottoms have more lightly overconsolidated by higher overburden pressure.

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

In this study, seepage/seismic behavior of a large river levee on alternately layered ground of sandy and
clayey soil was evaluated by a soil-water-air coupled finite deformation analysis code. The main findings
are as follows: 1) Focusing on the river level, the analysis during seepage and during/after an earthquake
was performed. The higher the river level, the larger the deformation in a direction toward the landside. 2)
If the water permeability of the sandy soil layer is as high as 'gravel', 8 hours after the river level rose, ground heaving which will lead to piping occurred near the landside toe. This is because the permeability of covering clayey soil layer is low and much water was supplied from the river to the sandy soil layer. 3)In the case of high permeability in the sandy soil layer as 2), during an earthquake, even when the river level is low, pore water is able to migrate in the sandy soil layer underlying clayey soil layer with low permeability. This results in liquefaction of the top of the sandy soil layer though the permeability is as high as gravel.

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

A simulation of triaxial shear tests on unsaturated silty specimens was performed under constant confining pressure and various drained and exhausted conditions starting from a single initial condition and passing through processes of suction variation and isotropic consolidation considering the triaxial test as an initial and boundary value problem. The simulation made use of a soil-water-air coupled finite deformation analysis code incorporating the SYS Cam-clay model as the constitutive equation of the soil skeleton and applying the average soil skeleton stress in the stress equation. The results showed that the coupling effect of the highly compressible air has a significant effect on the mechanical behavior. In addition, the results also explained other behaviors that would have been outside the capability of an analysis model that did not take account of factors other than air coupling such as suction. The authors wish to place special emphasis on the following findings:
(1) For simulation purposes, even using a soil water characteristic curve determined uniquely by the relationship between the degree of saturation and suction, it is still possible to calculate the increase in the degree of saturation for the drained and exhausted shear tests (under constant suction).
(2) A comparison of the experimental and calculated initial stiffnesses, volumetric strains, etc. showed that suction has an inhibiting effect on plastic deformation not only in drained and exhausted, but also in undrained and unexhausted conditions.
(3) For tests in which the volumetric restraint conditions of specimens were varied by controlling the air pressure under undrained conditions, results suggested that an introduction of gas leading to a rise in gas pressure within a highly structured ground may produce a risk of the ground displaying strain softening behavior. In the simulation, it was shown that this softening behavior can be represented in terms of structure decay as described by the SYS Cam-clay model.

Authorship：Lead author   Language：Japanese  

Language：Japanese  

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

Numerical simulation of the pore water pressure dissipation method was performed using the GEOASIA soil-water coupled finite deformation analysis code, which is capable of accounting for inertial forces, together with the elasto-plastic constitutive SYS Cam-clay model based on the soil skeleton structure concept, with the goal of quantitatively assessing the effects of this method as a liquefaction countermeasure. At the same time, an effort was made to improve/enhance the calculation efficiency of the GEOASIA analysis code by incorporating a macro element method, which up to this point has only been applied to consolidation problems. The main findings of this study are as follows: 1) the macro element method is capable of highly accurate approximation even for dynamic problems; 2) it is capable of reproducing the pore water pressure increase suppression effect associated with the pore water pressure dissipation method, even when a relatively coarse mesh is used; 3) it is capable of reproducing the suppression of the decrease in effective stress due to the pore water pressure dissipation method, along with the resulting reduction in shear stiffness and lateral ground movement and settlement; and 4), it is possible to efficiently design the pore water pressure dissipation method by first performing calculations using a 1-D mesh to determine the effective drain spacing prior to performing calculations using 2-D or 3-D meshes.

DOI： http://dx.doi.org/10.1016/j.sandf.2015.09.013

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

When simulating the vertical drain method using a soil-water coupled finite element analysis, a macro-element method can be used as a means of approximately applying the water absorption function of drains to individual elements. In this paper, the discharge function of vertical drains was added to the method by treating the water pressure in the drain as an unknown and adding a continuity equation for the drains to the governing equations. By extending the method in this way, the analytical results came to exhibit the well-resistance phenomenon automatically, depending on the analytical conditions. Numerical analyses were conducted after incorporating the proposed macro-element method into aquasi-static soil-water coupled elasto-plastic finite element method based on the finite deformation theory. The main conclusions are as follows:(1)the proposed method enables highly accurate approximations for problems involving material and/or geometrical nonlinearity and multilayered grounds; (2)the proposed macro-element method is capable of reproducing various phenomena that occur when the vacuum consolidation method is applied to a clayey ground containing a middle sand layer;(3)by following the formulation used in this paper,it is unnecessary to match the mesh division width to the drain arrangement and spacing. In addition, it is possible to obtain solutions that are minimally affected by the meshsize.

DOI： https://doi.org/10.1016/j.sandf.2015.09.012

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

The authors previously extended themacro-element method proposed by Sekiguchi to include water absorption and discharge function sand incorporated this into a soil-water coupled finite deformation analysis code capable of accounting for inertial forces. The primary objective of this study is to validate the ability of the proposed method to simulate actual ground behavior by comparing the simulation results with the actual measurements of the embankment loading of a soft peat ground improved with vertical drain sand vacuum consolidation. It was found that the proposed method is capable of comprehensively and closely simulating not only the magnitude of settlement, but also various ground behaviors,
including the deformation of the surrounding ground and porewater pressure distributions. Furthermore, additional simulations were performed to elucidate the effect of a continuous middle sand layer found to exist and to span the entire improved area at an actual embankment site.

DOI： https://doi.org/10.1016/j.sandf.2015.09.007

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

A large number of houses suffered from liquefaction-induced damages in recent large earthquakes due to lack of economical countermeasures. In this study, the shallow ground improvement, up to several meters deep, was proposed as an economical liquefaction countermeasure for houses. Based on the case studies, the design criteria of allowable tilt angles and penetration settlements of houses were proposed for the required level of serviceability against moderate and large earthquakes. The results of questionnaire survey, airborne LiDAR survey, and centrifuge model tests demonstrated that even a few meters of non-liquefiable layers in shallow ground could greatly reduce settlements and tilting of houses. A series of numerical analyses indicated that non-liquefiable layer of three meters thick below ground water table improved by solidification methods can prevent significant damages of houses. Furthermore, cost analyses were carried out for different ground improvement methods for both new and existing houses.

DOI： https://doi.org/10.1016/j.soildyn.2015.08.016

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

The construction of a test embankment on ultra-soft ground containing an approximately 50-m-deep soft peat layer with N-values of 0 to 1 did not result in catastrophic slip failure during construction but did cause substantial deformation of the adjacent ground. In addition, large-scale settlement in excess of 11 m occurred in the approximately 3 years following embankment construction. Based on field observations, it became evident that this large settlement was attributable to delayed compression of the deep peat layer, which was assumed at the design stage not to be subject to settlement. Based on laboratory tests and site investigations, it was deduced that due to depositions under continuous artesian conditions, this peat layer had an extremely low consolidation yield stress and was in a state such that even a slight increase in stress would result in large-scale compression. After confirming the ability of the analysis code based on soil-water coupled finite deformation theory, which included an elasto-plastic constitutive equation describing the behavior of the soil skeleton, to reproduce the observed ground behavior, the code was used to predict future settlement. These simulations were then used to evaluate the effectiveness of countermeasures aimed not only at improving stability during construction, but also at reducing residual settlement. The results of these analyses were applied in the planning of large-scale repair work performed on the test embankment. Also, when an embankment was subsequently constructed near the test embankment on similar ultra-soft ground, ground improvements were conducted prior to embankment construction as a countermeasure against residual settlement. In this paper, valuable field data related to these latter construction efforts is also presented.

DOI： http://dx.doi.org/10.1016/j.sandf.2015.02.010

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With the aim of expanding the soil skeleton-water coupled finite deformation analysis code mounted with the SYS Cam-clay model and capable of accommodating inertia forces to deal seamlessly with soils from the unsaturated to the saturated states, a new soil skeleton-water-air coupled finite deformation analysis method (u-pw-pa-sw formulation) based on the three-phase mixture theory was proposed. The following are the main observations obtained through computations performed under simple conditions using this new method. (1)Simulation of constant cell pressure undrained (and unexhausted) triaxial tests on dense sand specimens with a degree of saturation of 99.9%, which in reality could be considered to be 'saturated soil,' was carried out. It was shown that when the back pressure was not sufficiently large, the existence of air causes desaturation to take place due to the effect of volumetric expansion and no increase in the deviator stress is observed. It was confirmed that the results of this simulation agreed with experimental results. (2)Unlike the conventional method of analysis in which the degree of saturation is not explicitly made an unknown, the current method of analysis, in which the degree of saturation is explicitly made an unknown (u -pw -pa -sw formulation), was shown to be capable of expressing the increase in the degree of saturation even in the case of insular air saturation when the suction is 0.

DOI： http://dx.doi.org/10.1016/j.sandf.2014.12.004

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2011年東北地方太平洋沖地震により発生した地盤の液状化により、数多くの戸建て住宅が被害を受けた。本研究では、戸建て住宅を対象とした経済的な液状化対策として、浅層盤状改良工法の適用の可能性について検討した。既往の研究と同地震による戸建て住宅の液状化被害を調査し、液状化に対する戸建て住宅に要求される性能として、その傾斜角を、中地震では10/1,000（めり込み沈下量10cmに相当）以下、大地震では16.7/1,000（めり込み沈下量15cmに相当）以下とすることが適切であることを示した。また、被害調査と遠心模型実験を通じて、浅層盤状改良工法による液状化対策の効果を明らかにした。そして、一連の数値解析により、表層地盤の固化工法による地盤改良層厚を3m以上とすることで、液状化に対する戸建て住宅の要求性能を満足することを示した。さらに、浅層盤状改良工法の種類と改良深度、改良面積をパラメータとした経済性評価を行い、同工法の設計に有益な情報を提供した。

DOI： http://dx.doi.org/10.3208/jgs.9.533

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DOI： 10.1016/j.sandf.2012.11.003

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DOI： http://dx.doi.org/10.1016/j.sandf.2013.10.012

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DOI： 10.1016/j.sandf.2012.11.003

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

In order to solve large deformation problem of geomaterials, the SPH method is used which is
a kind of particle method based on the meshless Lagrangian scheme. The method can solve large deformation problems without mesh distortion. Moreover, it can handle the governing equations and existing constitutive models for geomaterials based on a continuum mechanics. To express various states of the soil, the elasto-plastic constitutive model taking account of soil skeleton structure is introduced into the method. In this paper, in order to verify the numerical scheme, a simulation of simple shear test is carried out. The obtained results are compared with theoretical solutions. Furthermore, the excavation problems for loose and dense sand ground are solved. From a series of the numerical results, the effectiveness of the method with the constitutive model of high performance is demonstrated.

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

In this study, the influence of brittle property of geomaterials on the failure behavior of the ground in an undrained bearing capacity problem was investigated numerically from the standpoint of taking the brittle behavior of cement treated soil as softening behavior of the soil element. The numerical analyses were performed using the soil-water coupled finite deformation analysis code GEOASIA mounted with the SYS Cam-clay model, which describes the soil skeleton structure at work. Cement treated ground and naturally deposited clay ground were modelled and compared, and it was found that they showed widely differing failure processes depending on differing initial conditions. Especially, it was found that when progressive failure in which strain localization region develops due to propagation of material failure occurs, even though the ground is composed of brittle materials such as cement treated soil, those brittle properties do not directly manifest in the load-settlement relationship. Additionally, the investigation revealed that, since every soil element on the slip lines does not reach its peak strength simultaneously when progressive failure occurs, post-peak material properties, i.e. the ratio of residual strength to peak strength and softening rate from peak to residual state, affect the bearing capacity of the ground.

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「砂圧入式静的締固め工法」は，地盤中に流動化砂を圧入・押し広げることにより，周辺地盤に強制的に圧縮・せん断を与え，締固め効果を期待する工法である。工法の性格上，地盤に変位や応力を与えることに伴い，近接の既設構造物に少なからず影響を及ぼす。この影響の程度を予測／評価するためには，土要素の平均有効応力変化に伴う圧縮挙動だけでなく，せん断応力に伴うダイレイタンシー挙動もより精度よく評価する必要がある。本研究では，自然粘土～中間土～砂を一貫して説明することが可能な弾塑性構成式(SYSカムクレイモデル)を搭載する水～土連成有限変形解析を用い，3次元条件で砂圧入締固めの過程を再現して解析を実施した。この結果，砂圧入式静的締固め施工時の，周辺砂地盤の地表面および地中発生変位の距離に伴う減衰(距離減衰)や，近接構造物に与える地盤反力(側圧)分布は施工位置からの距離に応じて減少することがわかった。

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DOI： 10.1016/j.sandf.2012.11.003

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In this research, we reproduced the vertical asymmetrical acceleration response observed at the ground surface at KiK-net measurement station IWTH25 (West Ichinoseki) during the 2008 Iwate-Miyagi earthquake using the finite deformation analysis code GEOASIA, which employs an elasto-plastic constitutive equation, the SYSCam-clay model, that incorporates the concept of soil skeleton structure. Also, it was found that the asymmetrical acceleration motions in the vertical direction measured at the ground surface at this location can be caused by a ground uplift phenomenon associated with loosening of heavily overconsolidated soils.

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Anti-seismic mechanism of typical loose sandy ground improved by the sand compaction pile (SCP) method was investigated using the geo-analysis code GEOASIA, which is a dynamic/static soil-water coupled finite element deformation analysis code incorporating the SYS-Cam clay model as a constitutive model of the soil skeleton. The mechanism was evaluated on the two types of earthquakes, i.e., the so-called Level 1 (L1) and Level 2 (L2) earthquake motions under 2-dimensional plane strain conditions. The main conclusions are drawn as follows. (1)Compared with untreated grounds, the deformation caused by earthquakes is suppressed in the SCP-improved grounds, both L1 and L2 earthquake motions. (2)Stress concentration occurs at the sand piles because the sand element at the piles exhibits hardening behavior due to plastic expansion.

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Seismic behavior of a coastal artificial reclaimed ground within the Port of Nagoya and antiseismic effects of two types of ground strengthening techniques were evaluated through numerical analysis. Use of the program GEOASIA for the numerical analysis enabled precise modeling of the targeted ground and consistent analyses of the pre-seismic, co-seismic, and post-seismic behaviors. Main findings are as follows. 1)Loose sand layers were subjected to large amount of lateral flow due to liquefaction during the earthquake, which led in turn to extensive damage to the revetment constructed on the reclaimed ground. 2) Steel pipe sheet pile cofferdam method is unlikely to be effective because the bending moment loaded on the steel pipes will exceed the yield stress during the earthquake. 3) Ground improvement using a jet grouting method will not contribute to damage reduction in the revetment area, but should drastically reduce the ground deformation around the improvement area.

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This study endeavors to predict the settlement that could occur in the future at a site where settlement due to embankment loading is already occurring at present. In the site studied here, large residual settlement of as much as 70 cm has already occurred in the 4 years since it entered into service. It is believed that settlement will also continue in the future because excess pore pressure is still present within the clay layers. Furthermore, according to the method of evaluation proposed previously by the authors, which is based on the sensitivity and compression index ratios, it can be judged that the ground includes clays that are sensitive to disturbance and have a strong possibility of large residual settlement. In this paper, simulation of the settlement observed up to now at the site as well as prediction of the settlement that could occur in the future was carried out by deducing the higher compressibilities possessed by the in-situ clays compared with the undisturbed clay specimens in the laboratory. The soil-water coupled finite deformation analysis was employed using the analysis program GEOASIA, in which the constitutive equation for the soil skeleton is mounted with the SYS Cam-clay model. In addition, the effect of modifying the vertical section of the embankment by overlaying in order to counter the settlement was also investigated by numerical analysis. The results showed that such a countermeasure cannot be expected to lead to faster consolidation and that it may require massive funding over a long period of time to cover the maintenance and management costs involved.

DOI： 10.3208/sandf.51.133

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人工島・海上人工埋立地に生活・経済基盤を依拠する我が国にとって，切迫する巨大地震に対する人工地盤の耐震性再評価や耐震強化は喫緊の課題である。しかし，人工地盤の大半が粘土でも砂でもない細粒分を多く含んだ中間土からなるが，このことだけを取りあげても，砂だけ，粘土だけを対象にするような要素研究の細分化が進んだ近代土質力学的視野では対応できない。要素を統合的・俯瞰的視野で捉える新しい現代地盤力学の進展とその成果の工学への還元こそが必要となる。本稿では，この観点から近代土質力学の課題と現代地盤力学の役割について述べる。

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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.

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本論文では，薬液注入・高圧噴射等のセメント固化改良工法等により，部分的あるいは離散的に改良固化が施された砂質地盤を想定して，地震を受ける場合の変形抑止効果を数値解析的に調べた．解析は土骨格の弾塑性構成式にSYSカムクレイモデル3)4)を用いた水～土連成動的／静的有限変形計算コード（GEOASIA）5)6)により行い，改良砂質地盤の地震中および地震後の挙動を調べた．また定性的ではあるが，系統的な結果を得るために規則的に改良体を配置し，実スケールにて解析を実施して，改良部が周辺地盤に与える影響も調べた．

Authorship：Lead author   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.

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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.

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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.

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The co- and postseismic behaviors of typical loose sandy ground and soft clayey ground improved by the sand compaction pile (SCP) method were investigated using a soil-water coupled finite element deformation analysis program incorporating the SYS-Cam clay model. The results indicated that the deformation caused by earthquakes was suppressed in the SCP improved grounds, irrespective of whether they were sandy or clayey. Although the surrounding ground was liquefied in the case of SCP-improved sandy ground, the confining pressure was maintained in the SCP interpile zone because of the compaction effect produced by the cavity expansion of the sand piles. In the case of the SCP-improved clayey ground, negative excess pore pressures appeared in the SCP sand piles because of the hardening that results from plastic expansion and stress was concentrated on them.

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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.

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The continuous behaviour of a ground-embankment system from the stage of deformation up to failure was predicted with respect to an actual test embankment that had been constructed in stages on a soft ground made up of peat and calcareous soil. The behaviour prediction was carried out by employing soil-water coupled finite deformation analysis, which also included simulation of the embankment construction process. The information used in the analysis was limited to such things as the results of soil tests on soil materials (peat and calcareous soil) sampled from the ground, including their sensitivity ratios, and the embankment's construction history. The SYS Cam-clay model was used in the constitutive equations of the soils to determine the material constants of the soils and the initial conditions of the ground, and the computations were performed under plane strain conditions. As a result, the computed profiles of W-type ground settlement and of slip surfaces running through the embankment were found to be in good overall agreement with the actual profiles measured at the site. Furthermore, we found that this slippage is attributable to the undrained shear response of the soil elements in the calcareous soil layer, where slippage begins to occur during embankment loading. In other words, the slippage is caused by the rapid softening behaviour caused by the degradation of structure after the effective stress ratio reaches the vicinity of the critical state line.

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The Nagoya port has reclaimed grounds of about 4500ha now, and has supported the economic activity of the postwar period of Japan. In the Chubu area including this Nagoya port, it is said that a trench type big earthquake occurs in high probability. In this paper, first, a reclaimed ground in the Nagoya port was reproduced numerically by using the geo-analysis code GEOASIA according to the construction history from the reclamation-by-drainage performed about 200 years ago to the present. In this calculation, the influence of the Tonankai earthquake which occurred in 1944 was also taken into consideration. Next, the Tonankai and Tokai linked-type earthquake assumed here from now on was inputted into this reclaimed ground by using the same analysis code in order to evaluate the co- and post-seismic behavior of the ground. The main findings from the results of the analysis were as follows. (1) In the linked-type earthquake assumed, liquefaction may occur even in diluvial sand layer whose N-values are comparatively large, and consolidation settlement of the layer may occur after the earthquake as well as the clay layer. (2) Quay wall may move about 3.5m horizontally to the sea side.

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2007年新潟県中越沖地震の際，東京電力柏崎刈羽原子力発電所では，底面が岩着された原子炉建屋近傍で局所的に大きな埋戻し土の沈下が生じたことが報告されている。本研究では，剛な構造物近傍において，地震時にこのような大きな沈下が確認された例が少ないことを踏まえ，地盤の拘束圧を実物に近づけることが可能な遠心力模型実験によって現象を再現し，近傍地盤では，構造物から離れた地盤と同様の土の圧縮による沈下に加えて，壁面から地盤が離れる際に主働すべりによる沈下が生じていることを把握した。さらに，遠心力模型実験を対象にGEOASIA によるFE 解析を実施し，沈下現象の再現を試みた。その結果，解析結果において，地盤のダイレイタンシーに伴う土の圧縮による地盤の沈下が再現されており，構造物の近傍における上述の主働すべりによる大きな沈下も概ね再現可能であった。

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自然堆積粘土の力学特性を把握するためには骨格構造概念が重要であり，骨格構造の働きを定量的・定性的に記述するためには，土台となる練返し試料による試験が必要不可欠である．本論文では，練返し試料の圧縮曲線に着目し，練返し時の含水比が及ぼす影響について検討した結果，以下の結論を得た．(1)液性限界よりも低い含水比で練り返した試料は，試料が固く練返しに大きな力を必要とするため過圧密土的な挙動を示す．(2)液性限界よりも高い含水比で練り返した試料は，構造が残存し嵩張った挙動を示す．(3)骨格構造を完全に喪失した練返し試料の作製に最も適した含水比は，液性限界である．

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A simple method that utilizes the results of laboratory tests has been proposed for judging soft clay grounds that are susceptible to large residual consolidation settlement due to embankment loading. It was found that there is a possibility of large long-term settlement if the sensitivity and compression index ratios of the clay material that constitutes the ground are equal to or more than 8.0 and 1.5, respectively. The compression index ratio is defined in this paper as the ratio (Cc/Ccr) of the steepest gradient of the compression curve of an undisturbed sample to that of a remolded sample. Through the SYS Cam-clay model, an elasto-plastic constitutive model that describes the actions of the soil skeleton structure, it was found that clays with large sensitivity and compression index ratios are characterized by initially highly structured soils initially and that decay/upgradation of the structure can occur easily due to plastic deformation. In addition, by following Schmertmann's graphic method for the compression curves of in-situ compression curve(1953), this paper proposes a method of deducing the in-situ initial conditions from the results of laboratory consolidation tests on undisturbed samples. These investigations revealed not only that large delayed settlement is facilitated in clays that have high levels of structure and fast rates of structural decay, but also that the Δe method and other simple methods of predicting settlement may underestimate the amount of settlement.

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This paper presents a new method of soil-water coupled finite deformation analysis of saturated soils that considers inertial forces. This method allows changes in the geometric shape of the soil to be taken into account and is capable of dealing with all types of external forces irrespective of whether they are static or dynamic. To be more specific, the paper describes the following points, which differ from the conventional methods: 1) the governing equations for saturated soil including the rate-type equation of motion containing a jerk term of the soil skeleton conforming to u-p formulation and updated Lagrangian, 2) derivation of a weak form of the rate-type equation of motion and discretization of the finite elements, and 3) use of the implicit time integration method for application of the conventional linear acceleration method (which assumes linear variation of acceleration) to the jerk term.
By mounting the elasto-plastic constitutive equation (SYS Cam-clay model), which can cover a wide range of soils and soil conditions, onto the above method of analysis, examples of simulation of dynamic/static triaxial laboratory testing of saturated soil specimens are described. The soil specimens were assumed to be medium dense sand under conditions of small-amplitude cyclic loading, partial drainage, and constant cell pressure. The simulation yielded the following results. (1) In the case of low frequencies, compaction occurs during loading and compression progresses over the entire specimen. (2) In the case of high frequencies, during loading and in the period in which wave propagation continues within the specimen after the end of loading, compaction occurs at the drained end of the specimen, whereas liquefaction occurs in its interior. After this stage, massive compression takes place within the specimen, leading to consolidation (consolidation after liquefaction).

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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.

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The effects of the rigidity of earth structures such as embankments on the deformation behavior of sand-clay laminated soil (top layer of sand, under-layer of clay) and embankment coupled systems during and after earthquakes were investigated. The investigation was carried out through static and/or dynamic soil-water coupled finite deformation analysis using the SYS Cam-clay model as the constitutive equation of soils. The results showed that the large-scale deformation behavior of the top sand layer during and after seismic activity is different from that of the clay under-layer depending on the rigidity of the embankment. If the embankment is made up of soft soil, the occurrence of liquefaction of the top sand layer during an earthquake is accompanied by large-scale deformation of the embankment itself, but the clay under-layer remains almost unaffected even after the earthquake. In contrast, if the embankment is rigid, while the sand layer is again subjected to liquefaction during the earthquake, the embankment load is transferred to the lower clay layer, leading to large-scale ground (clay layer) settlement after the earthquake has passed.

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Naturally deposited clay and loose sand are generally said to have a highly developed soil skeleton structure. Of the three skeletal determinants (structure, overconsolidation, anisotropoy), this paper focuses particularly on structure and argues that alongside structural degradation there is also an opposite process of upgradation. This upgradation process is then introduced as a new extension into the authors' existing SYS Cam-clay model, which incorporates the soil skeleton mechanisms into the original Cam-clay model as a base. Using this extended model, observations are made on the role of the upgradation process in leading to a ductility behavior in the naturally deposited clay and to a cyclic mobility behavior in the sand.

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Naturally deposited clay and loose sand are generally said to have a highly developed soil skeleton structure. Of the three skeletal determinants (structure, overconsolidation, anisotropoy), this paper focuses particularly on structure and argues that alongside structural degradation there is also an opposite process of upgradation. This upgradation process is then introduced as a new extension into the authors' existing SYS Cam-clay model, which incorporates the soil skeleton mechanisms into the original Cam-clay model as a base. Using this extended model, observations are made on the role of the upgradation process in leading to a ductility behavior in the naturally deposited clay and to a cyclic mobility behavior in the sand.

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A calculated case history concerning a soil of alternate layers of sand and clay is presented through a soil-water coupled computation employing the SYS Cam-clay model. Delayed consolidation settlement at this site has definitely been occurring as a result of embankment loading, and is in fact still continuing. In the computation, the delayed compression is due to a progressive breakdown in the clay skeleton structure. If there were to be an earthquake in the course of this delayed consolidation, even the medium-dense upper layer of sand would be certain to liquefy, resulting in considerable undrained shearing deformation in the clay layers beneath. Following the earthquake, the sand layer would consolidate within a few hours, but the underlying clay layers would remain subject to an additional consolidation settlement due to the earthquake for several tens of years.

Language：English  

This paper is a natural extension of the former paper (Asaoka and Noda, 2007), published by the same authors in the international workshop on Constitutive Modelling held in Hong Kong. The behavior of a naturally deposited soil in a delayed consolidation phase during/after and earthquake is presented as a soil-water coupled calculation example. Emphasis is laid throughout on the importance of an analytic technique that copes consistently with all soils, clay or sand, in all states, consolidated or liquefied/compacted, and is sufficiently all-round to cover both static and dynamic problems. The soil in the example consists of an 8m top-layer of sand and a 13m under-layer of alluvial clay, and has undergone more than 20 years of continuous consolidation settlement since being loaded with a highway embankment. Settlement loss exceeds 3m, and no end to the process is yet in sight. After showing that delayed compression of this kind is due to a progressive breakdown in the clay skeleton structure, this paper makes clear what will happen at this site if the top-layer of sand is liquefied by being struck by an earthquake and sustained consolidation/shear deformation then continues in the clay under-layer for several tens of years.

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パイルドラフトを弾性体，自然堆積地盤を水～土2相系の弾塑性体として，3次元有限変形解析を実施し，基礎形式（杭長・杭配置）・ラフト剛性等が，沈下量低減と杭の荷重分担率に及ぼす影響を調べた．杭が長い場合ほど高拘束で低圧縮性の地盤深部に荷重が伝達され，また杭が外側に均等配置された場合ほど地盤から受ける杭の摩擦抵抗が大きくなるため沈下抑制に効果的であるが，杭の荷重分担率が大きくなる,などを示した．

Language：English  

A long-term continuous consolidation settlement often observed in a natural soft clay foundation is numerically simulated using "super/subloading elasto-plastic constitutive model." The settlement behavior was found to exhibit accelerated rate of settlement several times during consolidation with a rise of excess pore water pressure under a constant applied load after the completion of the embankment. The likely causes of this lie in the progressive decay of soil skeleton structure of the clay which causes "compression accompanied by softening."

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To investigate a problem of bearing capacity of a natural clay, a soil-water coupled finite deformation analysis is performed with the elasto-plastic constitutive model that describes the effect of the decay of soil skeleton structure due to plastic deformation. From the computational results the findings are as follows: (1) In a structured clay soil, a load peak phenomenon appears, accompanied by a local circular slip field. (2) In a clay soil possessing anisotropy, this area of failure is more confined, and the peak is lower.

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The mechanism and characteristics of a static compaction pile method for sandy ground that is used as a measure against liquefaction, in which non-vibratory cavity expansion is gradually carried out from the bottom up, are numerically investigated using a soil-water coupled computation. The compaction procedure of the sandy ground is simulated employing a Super/subloading Yield Surface Cam-Clay model as an elasto-plastic constitutive model for sand. By introducing the concepts of soil structure, overconsolidation and stress-induced anisotropy and their evolutions, this model allows the description of a wide variety of sand behaviors using a single set of material parameters that are independent on density.
From the computational results, it is found that loose sandy ground is easily compacted/densificated because, in terms of sand elements, the soil structure of the sand is rapidly collapsed until the expansion takes place around the sand element and at the loading stages at which the casing pipe is driven in. Moreover, the shear characteristics of the ground are further improved because the overconsolidation ratio of the sand is increased cumulatively when the expansion is performed above the sand element and at the unloading stages at which the casing is pulled out.

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

Changes in soil structure and overconsolidation in highly structured natural deposited clay as a result of sampling and setting in laboratory tests, together with their effects on the subsequent mechanical behavior, are numerically investigated in terms of unconventional elasto-plastic mechanics. To describe the mechanical behavior, a Super/subloading Yield Surface Cam-Clay model is employed. This model allows a description of the decay of soil structure, loss/increase of overconsolidation and evolution of anisotropy with ongoing plastic deformation from the process of the soil sampling through the unloading with swelling up to the subsequent tests.
The clay sample, after being collected, mounted on the test apparatus, and subjected to isotropic unloading and/or one-dimensional unloading with swelling down to the first stage vertical loading level, displays a response to some degree different from that of the soil at the original sampling site, in the following respects. An overconsolidated sample subjected to isotropic unloading with swelling will display rewinding behavior in a subsequent undrained tri-axial compression test, and “secondary consolidation"/“delayed compression" in a one-dimensional consolidation test. In contrast, a sample subjected to one-dimensional unloading with swelling will not become heavily overconsolidated but will remain in a state of either slight overconsolidation or normal consolidation accompanied by destructuration, and will display unloading at the beginning of a subsequent one-dimensional compression test. The most important thing to note from the testing viewpoint is that one-dimensional unloading with swelling gives better results than isotropic unloading, in the sense that the subsequent compression test is better able to predict the in-situ “consolidation yield stress".
Artificially disturbed clay subjected to repeated undrained shearing after sampling suffers a significant loss of structure. This results in a drop in

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In critical state soil mechanics, the volume change behavior of soils has typically been analyzed based upon conventional "e-logp' relationships". However, compaction/densification of loose sand, for example, can sometimes occur even without any significant increase of mean effective stresses. This study presents a model which considers the fact that volume change can occur due to decay/collapse of the structure of soils. Taking into consideration the differences between clay and sand, this study models super-subloading surfaces together with rotational hardening using the modified Cam-clay model. The effects of decay of the soil structure, loss of overconsolidation and evolution of anisotropy are mutually discussed concerning their relationship with ongoing plastic deformation. Fundamental constitutive model responses are illustrated in the present study particularly for "compaction" of sand. Repeated application of low-level shear stress upon loose sand yields a huge amount of volume compression, which is due to the rapid collapse of the initial soil structure. Repetition of the loading also results in a rapid increase of the overconsolidation ratio. Drained and undrained shear behavior of the sand naturally changes remarkably along this densification/compaction procedure, which is also consistently predicted using a single set of soil parameters. Elasto-plastic behavior of the same sand at various densities is thus totally described in the present study in a single the-oretical framework based on soil parameters independent of density.

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

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Authorship：Lead author   Language：Japanese  

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The superloading yield surface concept applied to the original Cam-clay model is examined for the application to the one-dimensional consolidation problems of highly structured soils. When the proposed elasto-plastic constitutive model is taken to be the case for a structured soil, the one-dimensional consolidation computation clarifies the following : (1) Delayed consolidation should occur even under one-dimensional compression condition with a considerably low stress ratio when softening of the soil occurs with volume compression. The delayed consolidation is the consolidation process that has sometimes been referred to as "secondary compression". (2) The structure is always degrading as plastic deformation proceeds even within the period of "secondary compression". (3) The decay of overconsolidation to normal consolidation also proceeds with plastic deformation. In this sense, the degradation of structure can not be independent of the decay of overconsolidation. However, since the decay of overconsolidation is much faster than the degradation of structure in clay, then softening becomes possible with volume compression even under a considerably low stress ratio. Recovery of structure with time due to chemical bonding effects etc. in soil particles is beyond the scope of this study.

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

The superloading yield surface concept is newly introduced to the original Cam-clay model in order to describe some aspects of the mechanical behavior of highly structured soils, in which destructured soils are assumed to follow the original Cam-clay model. Following are typically those aspects: (a) structured soils are always "bulky" compared with destructured soils, and if they are in the normally consolidatcd state they always take their state variables outside the "Roscoe surface" of the Cam-clay model (b) when void ratios are the same, structured soils exhibit strengths higher than those of destructured soils; (c) for the same stresses, the void ratios of structured soils are greater than remolded soils. The structured state of a soil is simply defined as the size ratio of the original Cam-clay yield surface and the superloading yield surface that should lie above the Cam-clay yield surface. On the basis of "unconventional plasticity" theory the superloading yield surface concept, together with Hashiguchi's subloading yield surface concept, describes the degradation processes from both an overconsolidated state to a normally consolidated state and a structured state to a destructured state. These degradation processes continue gradually with ongoing plastic deformation. Since plastic deformation is irreversible, the decay of soil structure is also irreversible: The degraded state can not come back to the original state again through elasto-plastic mechanical operation alone. Chemical and/or thermal effects with "aging", that are said to newly generate both overconsolidated state and structured state without any change of stresses, are beyond the scope of this study.

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Even in normally consolidated or lightly overconsolidated clay foundations failures can occur some days/weeks after the load application is completed. Such an event can sometimes be attributed to creep-like failure. In this paper, the time dependent failure of a homogeneous normally consolidated soft clay foundation has been investigated using soil-water coupled elasto-plastic finite deformation analysis. The inviscid subloading surface Cam-clay model, which can express smooth transition from overconsolidated states to normally consolidated states during reloading, was used for the soil. With drained boundaries a clay foundation can experience failure, instead of consolidation, with the elapse of time after the end of load application. The foundation stays apparently stable for some time until it experiences a sudden failure. The occurrence of such a delayed failure in an elasto-plastic soil foundation is triggered off by the predominant pore water migration over the drainage from the soil mass due to softening that results in the increase of excess pore water pressure under this constant load. With time, the region in the foundation under higher excess pore pressure expands outward progressively from the centerline until failure. The pore pressure increase under constant load is similar to observed cases that registered increase in piezometric heads. When the magnitude of load at the end of construction is comparatively low, i. e. comparatively below the stationary load, only the consolidation process proceeds.

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In this study, in order to comprehend the progressive failure of an overconsolidated clay, triaxial compression tests under constant load application for the overconsolidated Kawasaki clay are carried out. These tests show, after a certain period of time, axial strain rate fluctuations with marked peaks until the specimen reaches outright failure. The experimental procedure is then numerically simulated using the soil-water coupled finite element technique. While the numerical simulation for the triaxial compression test under axi-symmetric conditions did not exhibit the same behavior as in the triaxial test (shear band formation and fluctuation of axial strain rate in the axial strain rate vs. axial strain plot), under plane-strain conditions it properly described the fluctuation of axial strain rate as observed in the experiments. Such fluctuations in the axial strain rate are closely related to the progression of the localized shear zones within the specimen. This behavior is attibuted to the "non-local" characteristics of saturated clays. Since the pore water supply to the localized shear zone can not always be sufficient due to Darcy's law which limits the gradient of global seepage head in the soil, the specimen exhibits varying strain rates. Tertiary mudstone pebbles can be idealized as heavily overconsolidated clay. The progressive failure of a heavily overconsolidated clay suggests that the behavior of crushed Tertiary mudstone is due to slaking at the contact points between the pebbles.

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

Non-linear consolidation deformation behavior of saturated clays under embankment loading (plane strain) has been investigated using numerical analysis. The governing equations are based on the finite deformation theory which considers both geometric non-linearity and material non-linearity and the finite element method is used for the solution procedure. The subloading surface Cam-clay model for finite deformation is employed for the non-linear material behavior of lightly/heavily overconsolidated clays. The clay foundation response to embankment construction under both the non-linearities is discussed within the Critical State Soil Mechanics framework. For overconsolidated soils, both the hardening and softening behavior above the critical state line (p'-q stress space) occur with plastic volume expansion. The area under the embankment slope reaches the normally consolidated state first during load application. In a lightly overconsolidated clay foundation, this area undergoes strong strain localization which can lead to physical failure of the structure. The embankment toe area of a heavily overconsolidated clay foundation exhibits a softening behavior with net volume dilatation at the end of the consolidation. The drained loading of a heavily overconsolidated clay foundation tends to give higher load bearing capacity than for undrained loading as in the case of lightly overconsolidated soils.

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

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

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学（東広島キャンパス）   Country：Japan  

著者らは，年代効果を疑似的／簡易的に付加・制御できる供試体作製方法を目指し，正の年代効果として少量のセメント添加を，負の年代効果として硝酸アンモニウム水溶液によるカルシウム溶脱を併用した供試体作製に取り組んできた．本報では負の年代効果の制御を目的に，セメント添加試料の溶脱時間がせん断挙動に及ぼす影響を調べた．その結果，セメント添加とカルシウム溶脱の併用で正負両方の年代効果を付加し，自然堆積軟弱粘性土と類似の特徴を有する供試体の作製に成功した．また，溶脱時間を変えることで非排水せん断強度やひずみ軟化の程度が変化し，負の年代効果を制御できることを見出した．

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学（東広島キャンパス）   Country：Japan  

静岡空港の滑走路端安全区域（以下「RESA」）の拡張整備では，空港既設盛土のり面上に新たな高盛土造成が計画されている．近い将来発生するとされる南海トラフ巨大地震に対し，静岡空港は「緊急輸送の拠点となる空港」相当の空港と考えられ，「発災後3日以内に，緊急物資・人員等の輸送受け入れ機能」を確保する耐震性が求められため，耐震性を検証した．その結果，想定される南海トラフ巨大地震に対しては，滑走路の変形は小さく，追加した高盛土についても損傷が小さいことから要求性能を有していることを確認した．

Event date： 2023.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学 ES 館 ES ホール   Country：Japan  

波浪作用下において生じる海底液状化現象の水～土骨格連成解析においては，その有効応力変動をもたらす要因として，①間隙水の圧縮性，②波浪の多次元性，③接線流速の影響が考えられている．本稿では，①②に着目し，u-p 形式の水～土連成変形解析を用いて，これらの要因の違いに由来する有効応力経路および弾塑性変形の差異を調べた．まず議論を簡単にするため，海底地盤を弾性体と見做した場合の解を示す．有効応力変動の要因を①に求める場合（間隙水の圧縮性を仮定した一次元解析）と②に求める場合（間隙水を非圧縮とする二次元解析）とで，同様の有効応力経路が表現されることを示す．また，上記の弾性解析と同一の境界条件のもとで弾塑性解析を実施し，①②の要因に応じて，海底地盤における有効応力低下域の回復・圧密（Solidification）進展の向きに明確な差異を生じることを示す．

Event date： 2023.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学 ES 館 ES ホール   Country：Japan  

液状化対策工法の一つとして知られるサンドコンパクションパイル工法は，地盤の密度を増大させる工法であるが，施工時に噴射する空気が地盤内に取り込まれるため，地盤の飽和度を低下させる副次的な効果も期待されている。一方で，液状化は緩い飽和砂地盤で生じるため，不飽和状態であっても緩い砂の繰返しせん断挙動に注目した研究が多く，密な不飽和砂の繰返しせん断挙動に注目した研究はあまり行われていない。本研究では，相対密度 64%程度で中密な場合と相対密度 84%程度で密な場合の豊浦砂供試体に対して，飽和度を 70～100%の範囲で系統的に変化させて，軸ひずみ振幅 1%の側圧一定・非排気非排水繰返し三軸試験を行った。その結果，密な場合は飽和度が 94%程度に低下しただけで，飽和状態と比べて繰返しせん断に伴う剛性低下が著しく抑制され，また飽和度が 79%と 69%の場合はほぼ同じ力学挙動を呈するなど，密な場合は中密な場合に比べて少しの飽和度低下で大きな改良効果が得られた。

Event date： 2023.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学 ES 館 ES ホール   Country：Japan  

本研究では，堆積盆地の三次元的な幾何形状が地震動の増幅特性ならびに地表加速度分布に与える影響について数値解析的に検討した．議論を簡単にするため，基盤層および堆積層はともに弾性体とし，基盤層と堆積層の剛性に明確なコントラストを与えた．これにより，剛性比に応じた地震動の増幅が基盤層と堆積層の境界で生じることとなるが，三次元的な堆積盆地ではさらに，実体波のレンズ効果と表面波の干渉
による強震動を生じることとなる．本稿では，地表の加速度応答および堆積盆地の伝達関数が，堆積盆地の幾何形状に応じてどのように変化するかを系統的に調べた．球形，楕円形，台形といった様々な盆地形状に対する時刻歴応答および周波数特性の比較から，1) 盆地が深いほど長周期地震動の増幅がより顕著になる，2) 楕円形盆地では球形盆地に対し加速度が小さくなる，3) 台形盆地では基盤傾斜による多次元効果が球形盆地より少ないことなどを示した．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

構造物と地盤の相互作用問題において，摩擦現象の固着状態～すべり状態の連続的な変化を記述可能なモデルとして，尾崎らの「時間依存性下負荷面摩擦モデル」が知られている．本稿では，同モデルに対し，上負荷面概念を新たに導入し，静止摩擦係数が動摩擦係数より大きい状態を構造の「嵩張り」と捉えた．塑性すべりによる摩擦係数の低下や時間経過に伴う凝着による摩擦係数の回復を，摩擦係数自体の発展則ではなく，接触面の内部状態変数としての「構造」の発展則として記述することで，物理的意味をより明確化できる．さらに，質点動力学計算を通じて種々の摩擦現象を再現し，提案モデルが既往モデルと同等の表現能力を有することを確認した．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

本研究では，圧縮作用下にある地盤で生じる座屈褶曲の形成メカニズムについて，系の接線剛性マトリクスの固有値変化に着目して考察した．弾性柱の一様圧縮では低次モードから順にゼロ固有値を経験するが（Euler座屈），剛性の異なる堆積構造を有する地盤の水平圧縮では高次モードが先にゼロ固有値を達成するため，高次の褶曲が容易に出現しうることを明らかにした．また，この高次モードの波長は層厚や材料特性のみで決まり，部材長非依存性を有することを，変形解析およびWinklerモデルとの比較を通して示した．この事実は，水平方向に無限に広がる実地盤において生じる褶曲の波長決定因子について議論する上で極めて重要である．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

相対密度64%程度で中密な場合と相対密度84%程度で密な場合の豊浦砂供試体に対して，飽和度を70～100%の範囲で系統的に変化させて，軸ひずみ振幅1%の側圧一定・非排気非排水繰返し三軸試験を行った。その結果，密な場合は飽和度が94%程度に低下しただけで，飽和状態と比べて繰返しせん断に伴う剛性低下が著しく抑制され，また飽和度が79%と69%の場合はほぼ同じ力学挙動を呈するなど，密な場合は中密な場合に比べて少しの飽和度低下で大きな改良効果が得られた。

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

本報では，地震動の継続時間の影響に着目し，耐震設計マニュアルを参考に継続時間の異なる地震動を作成して地震応答解析を実施し，河川堤防の地震被害に及ぼす地震動継続時間の影響を検討した．その結果，同一応答スペクトルを有する地震動であっても, 継続時間が長いほど地震被害が大きくなることを示した．これは砂質地盤の液状化や粘性土の乱れなど，地盤が示す弾塑性応答に起因する．設計用地震動は応答スペクトルで規定されることが多いが，強い弾塑性応答を示す軟弱地盤の場合は，特に地震動の継続時間の影響を考慮することが詳細な被害予測のためには重要であることを指摘した．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

本研究では，波浪外力作用下の海底地盤の応答について，地盤の弾塑性特性を考慮した解析を行い，その特徴的な挙動について考察した．半無限層厚を持つ弾性地盤は飽和状態（間隙水の非圧縮）の時に，波浪外力に対して平均有効応力・軸差応力ともに時間変動しないという理論解が得られているのに対して，弾塑性解析では，履歴・現応力依存の剛性のために十分な深さをもつ地盤であっても，いずれの諸量も変化しうることを示した．また，断続的な波浪作用下で海底表面から構造の劣化に伴う非排水的な平均有効応力の低下，そしてその後の体積圧縮を伴う平均有効応力の回復が解かれた．以上より，実地盤解析での地盤の弾塑性の考慮の重要性が示された．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

飽和地盤の水～土骨格連成解析は，間隙水の静的浸透を仮定するu-p formulationにより定式化されることが多いが，同手法により得られる解は，地盤の透水係数が大きい場合に不安定化することが知られている．本稿では，一次元問題を例にとり，このu-p formulationの不安定性はあくまで数値的なものであり，理論解自体は透水係数によらず無条件に収束することを示す．また，u-p formulationの理論解について，間隙水の相対加速度項を考慮したFull formulationの理論解と比較し，その特徴を整理する．

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡国際会議場   Country：Japan  

令和3年7月3日に熱海市の逢初川源頭部で盛土が崩壊し，土石流災害が発生した。この盛土崩壊のメカニズムを明らかにするために，弾塑性構成式SYS Cam-clay modelを搭載した慣性力対応の空気～水～土連成有限変形解析コードにより，盛土構築から崩壊までの一連過程の数値解析を行った。その結果，降雨時の地下水流入により盛土底部が塑性体積膨張を伴う軟化（吸水軟化）挙動を呈することで盛土全体が崩壊に至ることを示した。

Event date： 2023.5 - 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場（つくば市）   Country：Japan  

Event date： 2023.5 - 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場（つくば市）   Country：Japan  

令和3年7月3日に熱海市の逢初川源頭部で盛土が崩壊し，土石流災害が発生した．本研究では，この盛土崩壊のメカニズムを明らかにすべく数値解析を行った．具体的には，砂から中間土，粘土までの広範な土から構成される盛土について，降雨浸透や地下水流入に伴う変形・破壊挙動を解析できる手法として，土骨格の弾塑性構成式SYS Cam-clay modelを搭載した空気～水～土連成有限変形解析コードを採用し，地盤・水文調査結果に基づいて解析条件を設定した上で盛土構築から崩壊までの一連の過程の数値解析を行った．本稿では，その解析結果として，降雨時の地下水流入により盛土底部の土 が塑性体積膨張を伴う軟化（吸水軟化）挙動を呈することで盛土全体が崩壊に至ることを述べる．

Event date： 2023.5 - 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場（つくば市）   Country：Japan  

Event date： 2023.5 - 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場（つくば市）   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学   Country：Japan  

著者らは，間隙水の動的浸透を考慮可能なu-w-p formulation（以降，u-w-pと記す）に基づく水～土連成解析手法を開発してきた．本稿では，同手法を飽和弾塑性地盤のボイリング問題に適用した事例を示す．一次元解析では，ボイリングに至るまでの吸水膨張を伴う有効応力減少過程のみならず，その後の比体積増減を伴う地表面振動まで解くことができた．二次元解析では，上記に加え，局所動水勾配卓越箇所への流速集中や不安定化に伴う流線の乱れが解かれた．なお，以上の計算をu-p formulation（静的浸透を仮定する手法）で解くと計算が破綻することから，一連の現象を解く上でu-w-pが必須であることを確かめた．

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学   Country：Japan  

河川堤防の地震被害としては，砂質土基礎地盤の液状化被害に加えて，東日本大震災で数多く見られた粘性土基礎地盤上の堤体の液状化被害があり，砂質土と粘性土の両方に対して，地震前から地震中・地震後までを統一的に評価可能な変形解析手法が必要と考えられる．本研究では，複合負荷弾塑性構成モデルを搭載した空気～水～土連成有限変形解析コードを，河川堤防の耐震性能評価に用いることを見据えて，まずは砂質土基礎地盤を有する河川堤防を想定した動的遠心模型実験の数値シミュレーションを実施して，本解析コードの妥当性を検証した．

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学   Country：Japan  

沖積平野は，第4紀の沖積世に堆積した未固結の層（沖積層）から構成されるが，緩い砂質土や高含水比な有機質土・泥炭，鋭敏な粘土・シルトで構成され，軟弱な状態で堆積していることが多い．これら軟弱地盤では砂質土の液状化や粘性土の圧密沈下など，地盤工学的問題が生じやすい．しかし，国土の狭い日本では必然的に軟弱地盤上に構造物を建設し，生活を営むことが必要となる．種々の地盤工学的課題に対処するためには，自然堆積状態にある土の力学特性を正確に把握することが重要だが，堆積時のばらつき，サンプリング時の乱れや採取コストなどの制約から，自然堆積時と同じ状態で同質な供試体を数多く準備することは難しい．一般的には実験室で作成した再構成試料を用いて室内試験を実施することが多いが，再構成試料の場合，自然堆積過程において長い年月をかけて発達した年代効果の影響が考慮できず，自然堆積土が示す複雑な力学挙動とは異なることが知られている．本報では，年代効果として「セメンテーション作用」と「溶脱作用」に着目し，少量のセメントを添加した粘性土供試体を硝酸アンモニウム水溶液に浸漬してカルシウム溶脱させ，軟弱粘性土供試体の作製を試みた．

Event date： 2022.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学 ES 館 ES ホール   Country：Japan  

新潟地震以降，砂質土の液状化に関する研究が広く行われている．従来は応力振幅一定条件下で非排水繰返しせん断試験を行い，液状化するか／しないかの判定に加えて，液状化後の圧縮特性に関する研究が進められてきた．長時間継続地震動が危惧される昨今，液状化発生の有無だけでなく，液状化の程度がその後の挙動に及ぼす影響を把握することが重要である．しかし，応力振幅一定条件の場合，液状化到達後はひずみが急増して供試体は破壊に至るため液状化の程度を変えることが難しい．そこで本報では，繰返し載荷中に供試体が破壊しないように（液状化到達後も繰返し載荷が与えられるように），ひずみ振幅一定条件下で非排水繰返しせん断を行い，液状化の程度が液状化後の圧縮挙動および変形挙動に及ぼす影響を検討した．その結果，液状化の程度が大きいほど，液状化後の体積圧縮量は大きくなること，再載荷時に剛性回復が生じにくいことを明らかにした．

Event date： 2022.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学 ES 館 ES ホール   Country：Japan  

著者らは間隙水の相対加速度を考慮可能なu-w-p formulationに基づく水～土連成解析手法を開発してきた。本稿では，同手法の地盤の不安定化問題に対する有用性を以下の2つの点から示した。1) u-w-p formulationに基づく弾塑性有限変形解析手法を飽和地盤の不安定化問題（砂地盤～盛土系の地震外力による液状化問題，鉛直動水勾配作用下でのボイリング問題）に対して適用し，平均有効応力減少に伴い地盤が不安定化する条件下でも破綻することなく計算を継続できることを示した。2) 時空間離散化したu-w-p formulationの支配方程式および時間積分公式より構築した連立漸化式の数値安定性をスペクトル半径を用いて評価し，同手法の数値安定性が透水係数や時間刻み幅によらず，またu-p formulation（間隙水の静的浸透を仮定する手法）の適用不能域においても保証されることを，より一般性の高い形で示した。

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

臨海部の埋立工事で多く用いられる海底からの浚渫土砂は、高含水比で軟弱な粘性土を含むことから、埋立造成後地盤の圧密沈下が問題となる。著者らは別報で、このような浚渫土砂の早期圧密や減容化を目的に開発された真空井戸を用いた真空圧密工法に関する大型模型実験について、弾塑性構成式SYS Cam-clay モデル)を搭載した水～土連成有限変形解析コード（GEOASIA）を用いて三次元解析を実施し、実験結果をよく再現できることを示した（Validation）。これは、この解析コードが、①圧密開始前のコロイド状態の高間隙比と静水圧以上の間隙水圧を有する未圧密状態の土砂を表現できる上負荷面概念に基づく弾塑性構成式を用いること、②刻々の大沈下／圧縮量を正確に計量しつつ上澄み水も考慮できる水～土連成有限変形解析であること、③土の大圧縮に伴う透水性変化モデル（透水係数の間隙比依存性）を導入していること、そして④バーチカルドレーンもモデル化した三次元の詳細解析を実施したことに起因する。
本報では、計算コストの観点から三次元の詳細解析に代わり、この真空圧密工法に関する実務での簡易な多次元評価を実施すべく、浚渫土砂の大圧縮下で評価できるマクロエレメント法の拡張について述べる。具体的には、鉛直一次元的挙動の詳細解析と簡易解析の比較を通じて、 Barronの解に基づく土からドレーンに向かう透水性に及ぼす間隙比変化の影響が地盤の透水性のそれと異なる様子を示しつつ、土からドレーンに向かう透水性評価モデルを新たに提案する。なお、ここで用いるマクロエレメント法は、関口らによるものを拡張したもので、ドレーン内の間隙水圧を未知数とすることにより、ドレーンの集排水機能、つまり、ウェルレジスタンスを考慮でき、また、有限要素のメッシュ分割幅に制約を受けずに、同一メッシュを用いてドレーンピッチの効果などを調べることができる。

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

近年，降雨による斜面や盛土の崩壊が多発している。その崩壊要因には，不飽和土の飽和化や間隙圧上昇による強度低下，吸水による自重増加等が挙げられているが，詳細な崩壊メカニズムの解明までには至っていない。従前，降雨時の斜面・盛土の崩壊予測には，浸透解析と安定解析を組み合わせた手法が用いられる。しかし，斜面・盛土の崩壊メカニズム解明には，浸透解析で得られる応力状態を用いて安全率が 1 を超えるか否かで破壊の有無を与える安定解析は全く不十分で，降雨浸透に伴う土の変形から破壊に至る一連の過程を扱う力学体系が必要である。また，破壊現象は加速度運動を伴うため，たとえ外力が降雨であっても，慣性力を考慮する必要性は言うまでもない。さらに，変形から破壊に至る大変形挙動を数値シミュレートするには，土の変形とともに現れる幾何的非線形性を考慮する有限変形論に基づく解析手法が不可欠である。
以上の認識のもと，本研究では慣性力対応の空気～水～土連成弾塑性有限変形解析コードを用いて，降雨模型実験における不飽和斜面の変形・破壊シミュレーションを行った。

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

地盤の水～土骨格連成解析の多くは，間隙水の静的浸透を仮定するu-p formulation（以下，単にu-pと記す）に基づいて定式化されるが，同手法は，間隙水が動的にも浸透しうる高透水性土や，解析に用いる時間刻み幅Δt が小さい場合には計算不能に陥ることが知られている．殊に液状化解析においては，剛性低下に伴いstep 毎の変位増分が次第に大きくなるため，十分な計算精度を保つためにはΔt を小さく取る必要があり，u-p による計算が破綻する場合が多い．本稿では，著者らが開発してきた，間隙水の動的浸透を考慮可能なu-w-p formulation（以降，u-w-p）に基づく水～土骨格連成弾塑性有限変形解析手法を同模型実験の境界条件下で実行し，液状化による不安定化に伴いu-pによる計算が実行不能に陥る条件下であっても，u-w-pであれば安定して計算を継続可能であることを示す．

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

洋上風車基礎として適用例の多いモノパイルが共用期間中に受ける外力は，風と波浪による繰返し水平力を受ける．大口径で根入れ長が比較的短いモノパイルの水平繰返し挙動に関する研究は，欧州で砂地盤を対象にした研究が盛んに行われているが，日本近海で見られる軟弱な粘土層を対象にした研究は少ない．また，繰返し挙動に対する解析事例は砂地盤を含めても少ない．そこで，別報（その1）で取得した繰返し挙動実験を対象に再現解析を実施した．

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

沖積平野は，第4紀の沖積世に堆積した未固結の層（沖積層）から構成されているが，緩い砂質土や高含水比で間隙比の大きい有機質土・泥炭，鋭敏な粘土・シルトで構成され，軟弱な状態で堆積していることが多い．これら軟弱な地盤では砂質土の液状化や粘性土の圧密沈下など，地盤工学的問題が生じやすいが，国土の狭い日本では，必然的に軟弱地盤上で生活することが必要となる．種々の地盤工学的課題に対処するためには，自然堆積状態にある土の力学特性を正確に把握することが重要であるが，堆積時のばらつき，サンプリング時の乱れや採取コストなどの制約から，自然堆積時と同じ状態で同質な供試体を数多く準備することは難しい．一般的には実験室で作成した再構成試料を用いて室内試験を実施することが多いが，再構成試料の場合，自然堆積土の堆積過程において長い年月をかけて発達した年代効果の影響が考慮できず，自然堆積土が示す複雑な力学挙動とは異なることが知られている．
年代効果の再現方法として，これまでに微少量のセメント添加などや高温条件下での再圧密など，様々な取組みが行われてきている．本報では，海成粘土の形成過程に着目した新たな供試体作成方法を提案する．つまり，海底地盤ではプランクトンの遺骸などからなる炭酸カルシウム等による化学的結合が進展し，炭酸カルシウム含有率の増加とともに固結化が進む．そのため，海底から生じた地盤であればカルシウムを多く含んだ土であることが多く，セメンテーション作用が働く．さらに，長い年月の中で海底地盤は海進・海退作用や地盤隆起によって陸化し，地盤中を地下水がゆっくり流動することで間隙内の塩分やカルシウムが溶脱される．溶脱作用を受けると，せん断強度が低下することが知られている．本報ではこの「セメンテーション作用」と「溶脱作用」に着目し，セメント添加した粘性土供試体を硝酸アンモニウム水溶液に浸漬してカルシウム溶脱させる．また，その供試体を用いて各種室内試験を実施し，軟弱な自然堆積粘性土の特徴と比較した．なお，軟弱粘性土に共通する特徴として「高含水比」な状態にあり，圧縮挙動における「嵩張りと高い圧縮性」，せん断挙動における「ひずみ軟化挙動」を示すことが知られている．

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ（新潟コンベンションセンター）   Country：Japan  

軟弱粘性土を用いた埋立工事では，造成後地盤の圧密沈下が問題となる。筆者らは，残留沈下抑制のための圧密促進工法の一つとして，真空井戸・透水層・ドレーンを用いた真空圧密工法（BOLVAC工法）の有効性について検討を行っている。この地盤改良工法は，粘性土底部排水層に真空井戸を設置し，地表面未貫通のバーチカルドレーンを用いて真空井戸にかけた負圧が粘性土底部から伝播し，より効率よく圧密促進する方法である。改良効果を確認するため，既往文献では，粘土層厚さ2mを再現した28m3土槽（L2.5m×W1.6m×H2.4m）を用いた大型模型実験を行った。本報では，その模型実験結果の3次元FEMによるシミュレーション解析に基づき，地盤改良効果の検証結果を示した。

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：関東　オンライン   Country：Japan  

降雨による地盤・土構造物の被害が毎年発生している．また，大地震も断続的に起こっている．さらに，2004年の新潟県中越地震と台風23号および2009年の駿河湾地震と台風9号のように，地震と降雨がほぼ同時に起こった事例もあり，このように地震と降雨の複合外力に対して地盤・土構造物の性能評価を行う必要性が高まっている．本稿では三相系弾塑性有限変形解析により，地震と降雨の複合外力を想定して，河川水位と堤体の飽和度の違いが堤防の地震時の力学挙動に与える影響について評価した．その結果，河川からの浸透による堤体の飽和度上昇だけでなく，河川水位に対応する表面力が堤体を堤内側に押す影響も大きいことを示した．

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：関東　オンライン   Country：Japan  

熊本地震では，阿蘇カルデラの北西部に約10kmにわたる帯状の陥没性亀裂が発生した．著者らは，阿蘇カルデラ内の旧湖底が形成する「地層不整形性」およびその上に堆積する「軟弱粘性土の存在」に着目した二次元弾塑性地震応答解析を実施し，これらが阿蘇カルデラ内の陥没性亀裂被害を引き起こした要因であることを示した．本報では，上記に加えて，熊本地震の特異性，つまり震度7の強い揺れが時間を空けずに発生し，さらに後発の本震が長周期成分を多く含んでいたことも陥没性亀裂発生の重要な要因の1つであることを弾塑性地震応答解析によって示した．

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：関東　オンライン   Country：Japan  

高度な安全性が要求される球形ガスホルダーの余震に対する耐震性への影響を検討し，かつ地震復旧時の使用可否判断のための維持管理基準策定を目指すべく，最大余震を想定して傾斜したガスホルダーの耐震性を評価する．ホルダーの各部材を評価する解析は，支持構造部の材料・幾何学的非線形性および応答機構を考慮しかつ非線形ダンパーを扱うため極めて非線形性が強いものになり，かつ，3Dモデル解析には多大な労力が必要となるため，Pushover解析から非線形ばね特性を反映した1質点ばね解析を用いた簡易な評価手法を提案した．その結果同手法により，余震耐震評価上許容される最大傾斜を安全側に求めることが可能であることを示した．

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：関東　オンライン   Country：Japan  

堆積盆地が不整形な基盤形状を有する場合，堆積層内での加速度増幅や実体波のレンズ効果，表面波の干渉によるエッジ効果を生じるため，地表面では局所的な強震動や長時間に亘る揺れの継続を生じることが知られている．しかし，工学的には，計算コスト等の制約から，三次元問題として評価されることは少なく，簡便な低次元モデルを用いて地震応答解析が行われる場合が多い．そこで本稿では，三次元問題を直接解いた場合と，低次元モデルとして解いた場合でその応答を比較し，簡易モデルの解は三次元モデルに対して応答加速度は大幅に過小評価され，そのスペクトル特性も全く異なることを示すことで，三次元解析による応答評価の重要性を指摘する．

Event date： 2021.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

降雨による地盤・土構造物の被害が毎年発生している。また，大地震も断続的に起こっている。さらに，2004 年の新潟県中越地震と台風 23 号および 2009 年の駿河湾地震と台風 9 号のように，地震と降雨がほぼ同時に起こった事例もあり，このように地震と降雨の複合外力に対して地盤・土構造物の性能評価を行う必要性が高まっている。本稿では空気～水～土連成有限変形解析により，地震と降雨の複合外力を想定して，河川水位と堤体の飽和度の違いが堤防の地震時の力学挙動に与える影響について評価した。その結果，河川からの浸透による堤体の飽和度上昇だけでなく，河川水位に対応する表面力が堤体を堤内側に押す影響も大きいことを示した。

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

不整形な基盤形状を有する堆積盆地の地震時応答は，堆積層内での加速度増幅に加え，基盤層と堆積層の境界面での地震波の屈折によるレンズ効果，盆地端部において生成された表面波が実体波と干渉するエッジ効果などを伴う．このため，地表面においては局所的な強震動や長時間に亘る地震動の継続を生じ，均一な堆積層を想定した場合と較べて被害が甚大化することが知られている．本報では，弾塑性二相系解析手法による三次元堆積盆地の地震応答解析結果を紹介する．堆積層として飽和した緩い砂地盤／軟弱粘性土地盤の材料定数を与えた解析により，緩い砂地盤においては液状化の発生のため波が伝わりにくくなって「スロッシング」現象が生じる一方，粘性土地盤においては顕著な増幅を生じるなど，堆積盆地の弾塑性性状に応じて地震時の応答が全く異なることを示し，地震応答解析における地盤の弾塑性特性ならびに水～土骨格連成の効果（体積拘束）を考慮することの重要性を指摘する．なお，著者らは別報において，三次元不整形性を有する堆積盆地を対象に一相系微小変形線形弾性解析を実施し，不均一な堆積構造に起因した波動伝播を解くとともに，簡易モデル（一次元・二次元モデル）との比較を通して，三次元解析の重要性を指摘している．

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

熊本地震では，阿蘇カルデラ内の北西部に約10kmにわたる帯状の陥没性亀裂が発生した．陥没性亀裂の発生原因として，地下空洞の圧壊，地表地震断層，地盤深部における大規模な地質学的ブロックの水平滑動，断層運動など様々に考えられてきたが，その明確な痕跡は見つかってはおらず，未だ原因の特定には至っていない．本報では，阿蘇カルデラの陥没性亀裂の発生メカニズム解明を目的に，旧湖底が形成する「地層不整形性」およびその上に堆積する「軟弱粘性土の存在」に着目し，これらが表層地震被害に及ぼす影響を弾塑性地震応答解析によって調べた．

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

地盤の水～土骨格連成弾塑性有限変形解析コードGEOASIAを用いて，水平圧縮作用下にある海底地盤の変形を解き，デコルマの形成過程を数値解析的に再現した．弾塑性構成式としてSYS Cam-clay modelを用いるとともに，続成作用により骨格構造が発達した中間土を想定した材料定数および初期状態を与えた．解析の結果，時系列順に(a)imbrication，(b)デコルマの発生と剥ぎ取られた上盤側でのせん断ひずみの累積，(c)2本目のデコルマの発生（底付け付加の予兆）が解かれることを示した．さらに，材料の塑性圧縮に起因する正の過剰水圧の発生や変形の局所化に伴う地震動の生成が解かれることを確認した．

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

波浪外力作用時の海底地盤の安定性照査にあたり，波浪の長期的な繰り返し作用による「海底液状化現象」を適切に評価するためには，地盤の材料非線形性・履歴依存性を評価可能な弾塑性力学に基づく数値解析手法が必要となる．本稿では，骨格構造概念に基づく土の弾塑性構成式SYS Cam-clay modelを用いた数値解析を実施し，地震時の液状化と同様，(1)圧縮性間隙流体を有する海底地盤の一次元波浪作用時の変形解析，(2)非圧縮性間隙流体を有する海底地盤の二次元波浪作用時の変形解析を実施し，地盤の初期状態が密であるほど，また，波浪振幅が大きいほど有効応力が大きく低下することを明らかにした．

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

地盤に対し水平圧縮が作用すると，衝上断層群（imbrication）が形成される．本報では，弾塑性地盤力学に基づく圧縮変形場でのimbricationの形成解析の事例を紹介するとともに，模型底面に一様圧縮を伴う変位速度分布を与えた計算においては，imbricationをその発生順序（piggyback型，overstep型）も含めて再現可能であることを示した．また，境界条件および材料定数がimbricationの発生形態（発生間隔，角度）に及ぼす影響についても検討した．

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

断層が形成された地盤の母岩部と断層面近傍では強度差が生じる調査結果が得られる。本報では，地盤の隆起・傾斜によって正断層群が形成された地盤を対象とし，弾塑性計算によって地盤強度を調べた。計算には，骨格構造の働きに着目した土の弾塑性構成式SYS Cam-clay modelを搭載し，慣性力を考慮する水～土骨格連成有限変形解析コードGEOASIAを用いた。その結果，断層形成時には，塑性変形によって骨格構造を喪失するため強度は低下するが，その後の続成作用によって地盤が固結すると，断層形成時における骨格構造の喪失度合いの違いから，母岩部の強度は回復し，断層面近傍との強度差が生じる可能性を指摘した。

Event date： 2021.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

平成30年7月豪雨や令和元年東日本台風をはじめ，降雨による斜面や盛土の崩壊が多発している。本稿では，降雨による斜面や盛土の崩壊メカニズム解明を見据え，緩い不飽和シルト三軸供試体を荷重一定条件下でサクション低下と間隙圧上昇により吸水破壊させる実験を行った。サクション低下過程では，サクション低下開始時の軸差応力が大きいほど軟化の程度が大きく，サクション0kPaの排気排水三軸圧縮試験結果よりも軸差応力が低下すること，また間隙圧上昇過程では，骨格応力経路で限界状態線に到達する辺りで急激に軸変位が進展し，軟化することを示した。

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

熊本地震(2016)で発生した，阿蘇カルデラ内の北西部に約10kmにわたる帯状の陥没性亀裂に関する地震応答解析から，以下の結論を得た．
(1) 地層不整形性を考慮すると，(a) 深部から浅部へと伝播する実体波の焦点効果，(b) 長周期な表面波の励起と滞留，(c) 実体波と表面波が表層の特定場所で起こす増幅的干渉(エッジ効果)が生じた．このため，波動伝播が複雑となり，地盤内の特定箇所で揺れが大きくなった．
(2) 湖成粘性土層は軟弱な状態にあったため，地震による繰返し載荷によって容易に平均有効応力が減少し（剛性が低下し），地盤の固有周期を増加させた．
(3) 前震によって固有周期が増加した地盤に対して，長周期成分を多く含む本震が連続発生したことによって，地震動の長周期成分が著しく増幅された．この長周期の大きな揺れが，表層における陥没被害を発生させた．
つまり，阿蘇カルデラの陥没性亀裂被害は，上記(1)(2)(3)のすべての複合的作用により発生したこと，換言すれば，いずれかの要因が1つでも欠けていれば発生しなかった可能性があることを解析的に示した．

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

水平圧縮を受ける地盤においては，構成材料や境界条件に応じて，多種多様な地形が生じることが知られている．地盤内での単一の変位不連続に限定しても，発生角度が45°以上の「逆断層」，45°未満の「衝上断層」，水平に滑動する「デコルマ」が存在する．さらに，これらのすべり線が複数生じて地盤のpartitioningが進むと，共役なすべりに挟まれたブロックが隆起する「pop-up」や，平行な衝上断層群である「imbrication」など，さまざまな断層変位地形が形成されてゆく．このような地形の非可逆的かつ多段階に亘る形成過程を数値解析により解くためには，(1)地盤材料の材料非線形性，とくに軟化現象を表現可能な弾塑性構成式，および(2)地盤の形状および状態の変化を刻々と追跡可能な有限変形理論に基づいて解析を行う必要がある．本報では，端緒的ではあるが，著者らが開発した(1)(2)の点および間隙水の存在と慣性力を考慮可能な地盤の変形解析コードGEOASIAにより，上に挙げた種々の圧縮地形の形成解析を行った結果を示す．

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

地盤内部に非一様な堆積構造が存在する場合，地盤内の波動伝播は複雑なものとなることが知られている．とくに堆積盆地においては，堆積層内での加速度増幅や実体波のレンズ効果に加えて，盆地端部において生成された表面波との干渉に伴うエッジ効果により局所的に強い揺れが生じるとともに，長時間に亘り揺れが継続することが知られている．そこで本報では，三次元球形盆地を対象に一相系弾性・二相系（水～土連成）弾塑性地震応答解析を実施し，堆積構造の三次元性および地盤材料の弾塑性および間隙水の存在がその震動特性に及ぼす影響について調べた．

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

地下深部で横ずれ断層が変位すると，その直上に堆積した表層地盤内にフラワー構造が発達し，地表面ではリーデルせん断が生じる。著者らはこれまでに，リーデルせん断の形成過程を三次元弾塑性変形解析により解き，横ずれ断層上の屈曲部の幾何的な変形場の違いにより性質の異なる断層変位地形が形成されることを示してきた。本稿では，実断層上のランダム凹凸を模擬した境界条件を設定した解析事例を示す。
ランダムな断層線形状を複数生成して解析を実施したが，いずれのケースにおいてもフラワー構造の発達起点が「断層線の傾斜が最大となる拘束性屈曲」となることが確認され，断層線のトポグラフィに基づく断層変位時の変形卓越箇所の推定可能性が示唆された。

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：中部　オンライン   Country：Japan  

東日本大震災では，東京湾沿岸部の埋立地盤において広範囲に液状化被害が発生した．千葉県では本震に加えて29分後に最大の余震が襲い，余震時に噴砂などの液状化被害が拡大したことが報告されている．著者らはこれまでに，弾塑性構成式SYS Cam-clay modelを搭載した空気～水～土連成有限変形解析コードを用いて，砂地盤の地下水位以深の飽和域が本震により圧密排水（塑性体積圧縮）し，この水が浅部不飽和域に供給されて飽和域が拡大（地下水位が上昇）するために，余震時に液状化被害が拡大し得ることを示した．本稿では，砂地盤の地下水位上昇に加えて，飽和域の過剰間隙水圧上昇に注目した数値シミュレーションを実施して，両者の関係性を明らかにした．

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：中部　オンライン   Country：Japan  

水～土骨格連成解析は多くの場合u-p formulationと呼ばれる手法で定式化される．これは，間隙水の静的浸透の仮定により方程式系を縮小する近似解法であるが，間隙水の運動を準静的に取り扱う代償として，高透水性土の連成問題のような間隙水の動的浸透を伴う諸問題への適用は著しく制限される．そこで著者らは，u-w-p formulationに基づく水～土連成問題の支配方程式を静的浸透の仮定なしに直接離散化して解く解析手法を新たに開発してきた．昨年度までの報告では，本手法を低透水性土～高透水性土の一次元動的変形問題に適用し，高透水性土において非調和な振動現象の出現が解かれることや，解析初期に生じる「鉛直荷重と即時水圧の不一致」が固液相慣性力による荷重分担の帰結として理解されることを示してきた．本稿ではその続報として，即時水圧発現後の水圧変動における二段階遷移現象を取り上げ，これが「固液二相質点系」の運動を解いて求まる2つの指数関数解の収束速度の違いからも説明できることを示した．

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：中部　オンライン   Country：Japan  

放射性廃棄物処分施設の人工バリアにはベントナイト系材料を用いることが有力視されている．人工バリアの力学挙動評価では，弾塑性構成モデルの一つである修正Cam-Clayモデルを用いた検討が行われている．著者らは，膨潤性が非常に高い材料であるベントナイト系材料への弾塑性モデルの適用性については，力学挙動を適切に分析評価してから用いる必要があると考えている．そこで，本検討では，日本原子力研究開発機構の緩衝材基本特性データベースで一般公開されているベントナイト系材料の一次元圧縮試験結果及び圧密非排水三軸圧縮試験結果を対象に圧縮及びせん断挙動を分析し，土の骨格構造概念を記述する弾塑性構成モデル，SYSカムクレイモデルの適用性について検討を行った．

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： 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： 2020.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Authors have discovered inertia-induced phenomena in one-dimensional dynamic deformation problem, i.e., damped oscillation in settlement-time relation and inconsistency between vertical load and immediate pore water pressure, based on u–w-p formulation. The present study indicates that the u–w-p governing equation reduced to the damped wave equation whose solution are expressed as a superposition of several modes with different eigenvalues exhibiting overdamping ~ damped oscillation successfully simulates the inertia-induced phenomena.

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei, Taiwan   Country：Taiwan, Province of China  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：香川大学幸町キャンパス   Country：Japan  

近年，豪雨による斜面や盛土等の不飽和地盤・土構造物の崩壊が相次いで発生し，その被災メカニズムの解明が強く求められている．不飽和土の力学挙動を把握するためには，水分特性を把握することが必要である．不飽和土の水分特性の主な特徴としては，吸排水時のヒステリシス性と間隙比依存性が挙げられる．本研究では，間隙比依存性（体積圧縮時）の水分特性に注目して，不飽和シルトの排水条件および非排水条件の三軸試験を実施した．

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Reinforcement of soils using tension resisting elements is an actual and alternative solution for ground improvement and stabilization issues both for engineering and economic purposes. It is well-known that discrete flexible fibers act like plant roots and give the possibility to increase the strength and stability of soils. Prevalence of effectiveness of soil reinforcement with fibers started almost 15 years ago. However, there are not enough studies for describing the effect of fibers on soil behaviour and techniques of application of fiber-reinforcement in practice. This study was targeted on obtaining the behaviour of fiber-reinforcement of sandy materials with different relative densities and find out a more suitable method for specimens' preparation with the vision of future application on construction site.

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：香川大学幸町キャンパス   Country：Japan  

地すべり移動体の内部では，複数のリストリック正断層が平行に形成されて断層群を成すことも多い．本報告では，海底地すべり移動体内に存在する正断層群形成過程に関する数値解析的検討結果について述べる．解析には骨格構造概念に基づく土の弾塑性構成式SYS Cam-clay modelを搭載した水～土骨格連成有限変形解析コードGEOASIAを用い，固結状況が異なる３つの水平堆積した海底地盤（地盤１：堆積直後の状態，地盤２：未固結～半固結状態，地盤３：固結状態）を対象として，地盤傾斜時の挙動を調べた．ここでは，地盤は堆積後，続成作用により固結が進行して強度が増加する点に注目した．すなわち，堆積完了時の状態を基準とし，続成作用が進行すると，土粒子実質部分（間隙比）は変わらないが，セメンテーション等により土の骨格構造が発達すると考え，固結状況の違いを土の骨格構造の発達度や発展速度の違いとして表現した．

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：香川大学幸町キャンパス   Country：Japan  

日本の国土は起伏に富んでいるため，可住地が狭く，都市機能が沖積平野に集中している．平野部は一般的に地下水位が高いことに加えて，堆積年代が若いことから地盤が軟弱であることが多く，地震時に液状化をはじめとする地盤災害が発生する危険性が高い．人口・資産が集中した区域で河川堤防が被災し，決壊すると，甚大な浸水被害につながってしまうため，河川堤防の耐震性照査および適切な対策が重要である．しかし，従来の地震に対する耐震性能照査や設計は，静的照査法に基づき，砂質基礎地盤の液状化に伴う沈下量が外水位を超えないかどうかの判定のみであった．東日本大震災の被害調査を受けて，粘性土基礎地盤上の堤体の液状化が注目され，基礎地盤の液状化に加えて，堤体の液状化による沈下・変形も照査の対象事象に含めることが検討されているが，それでもなお不十分で，あくまで堤体材料（砂質土）の液状化であり，粘性土自体の地震変状や不安定化は考慮されてはいない．本報では，砂質土が卓越する断面および軟弱な粘性土が厚く堆積する断面上の河川堤防に対して，L1地震動およびL2地震動を入力した時の地震応答解析を実施し，軟弱粘性土地盤の地震時挙動の把握を試みた．使用した解析コードは，土の骨格構造とその働きの差異によって砂から粘土，両者が混在した中間土を同じ理論的枠組みで記述する土骨格の弾塑性構成式SYSカムクレイモデルを搭載した水～土骨格連成有限変形解析コードGEOASIAである．

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Soft clay foundation often shows long-term large settlement under embankment loading as the compressibility is large. On the other hand, the clay foundation has been considered to be safe for dynamic problem. However, the recently investigated results showed that clay foundation showed remarkable loss of rigidity due to earthquake, which leads to tremendous seismic damages, as seen in the 1957, 1985 Mexico earthquakes and the 2015 Nepal earthquakes. These areas possess the soft lakedeposits consisting of soil types with extremely high water contents, namely, soft and sensitive clays. Therefore, it is important to grasp both static and dynamic mechanical properties of naturally deposited clayey materials. To this aim, it is indispensable to carry out various systematic experiments using the undisturbed soil samples. However, it is difficult to prepare a number of homogeneous soft clay samples, due to the problems of variability of quantities during sedimentation, sampling disturbance and high expense of boring survey. Therefore, in this study we focused on cementation reaction, in order to artificially produce the soil sample having similar characteristics to those of naturally deposited soft clay. By doing so, while maintaining the reproducibility of the specimen, it might be possible to perform a large amount of systematic experiments, and also to conduct such model experiments as impossible in the past. Although numerous experimental studies have been conducted to reproduce the natural soft clay with cement, the cement was directly added to soil in most cases. As the result, the solidification effect was so strong that localized failure occurred in the soil specimen due to cracking followed by sudden decrease of shear stress with no increase in excess pore water pressure. So, in terms of the necessity to reduce the solidification effect, we newly attempted "addition of hydration reaction controlled cement" and "calcium leaching" to represent similar characteristics to soft clay material. In this report, we discuss the influence on mechanical properties when hydration reaction controlled cement is added to clayey soil.

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Reinforcement of soils using tension resisting elements is an actual and alternative solution for ground improvement and stabilization issues both for engineering and economic purposes. It is well-known that discrete flexible fibers act like plant roots and give the possibility to increase the strength and stability of soils. Prevalence of effectiveness of soil reinforcement with fibers started almost 15 years ago. However, there are not enough studies for describing the effect of fibers on soil behaviour and techniques of application of fiber-reinforcement in practice.
This study was targeted on obtaining the tendency for fiber-reinforcement of sandy materials and find out a more suitable method for specimens' preparation with the vision of future application on construction site.

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sitges(Barcelona), Spain   Country：Spain  

In the 2011 off the Pacific coast of Tohoku Earthquake, it is reported that, in Chiba prefecture, the big aftershock occurring 29 minutes after the main shock caused expanding the liquefaction damage in the sandy ground. In this study, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation SYS Cam-clay model, it is shown that groundwater level rise due to main shock may expand liquefaction damage during aftershock.

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sitges(Barcelona), Spain   Country：Spain  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sitges(Barcelona), Spain   Country：Spain  

In this study, to examine mechanical behavior of unsaturated soil, a series of triaxial tests was conducted and the soil-water-air coupled finite deformation simulation was performed. The simulation made use of a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation, SYS Cam-clay model, in which suction effect is newly taken into account, and a soil water characteristic (SWC) model which is dependent on void ratio. The simulation treated a triaxial test as the solution for an initial and boundary value problem. A series of processes of suction decreasing, isotropic consolidation, and exhausted-drained shearing was simulated from a single initial condition using a single set of material constants.

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Numerical simulations of cyclic water absorption-drainage triaxial tests were performed using a soil water characteristic (SWC) model taking trapped air into consideration. It was demonstrated that a mere
consideration of transition between trapped air and continuous air in the SWC model allowed us to express
the hysteresis of the saturation degree during water absorption-drainage. In addition, unexhausted and
undrained triaxial compression tests of two specimens with the same zero suction but with different
saturation degree due to difference in water absorption-drainage history were well simulated.

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

This paper proposed a new framework in elasto-plastic theory for soils called "combined elasto-plastic constitutive model." This framework allows the SYS Cam-clay model, which can describe the mechanical behavior of naturally deposited clayey soils, and the non-associated Drucker-Prager model, which has mainly simulated the undrained shear behavior of sandy soils, to simultaneously work within a single model. This paper introduced the basic formulation of this new framework and demonstrated that the proposed model could produce typical sand and clay behaviors.

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

2008年岩手宮城内陸地震時に荒砥沢ダムでは，底部監査廊で最大加速度1024Gal，中段コア部と最上部天端ではそれぞれ，535Gal，525Galの記録が得られた．ダム基礎で1000Galを超 える記録は異例であり，基盤に対する堤体の応答倍率が1を大きく下回るのも異例である．論文では，堤体材料の動的変形特性を広範なひずみ領域で説明できる弾塑性構成式を用いて水～土連成の有限変形解析を実施し，①応答倍率が0.5倍にまでも低下する現象は堤体材料の履歴減衰が原因で，②ダム基礎での1024Galの観測記録（E+F）は，強い非線形応答時のダム内部での反射・屈折現象を反映しており，入力地震動（E）は最大500Gal程度であったことを明らかにした．

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

河岸構造物の崩壊や堤体基礎の沈下を考慮することにより，その浸水域が大きく変化し，蜆川流域の堤体基礎が沈下するが河岸構造物は機能した場合には，蜆川右岸における堤体基礎の沈下量が大きいために蜆川北部に浸水が集中する．また，蜆川流域の堤体基礎が沈下し，堤体天端に併設されている直立堤も崩壊した場合には，浸水範囲はさらに拡大し，浸水深も深くなることがわかる．このように，耐震化未整備区間では強震動の影響によって護岸などの沈下が生じ，これにより津波浸水域は大きく拡大し得ることを定量的に示した．このことは河岸・海岸構造物の耐震化の重要性を示していることはもちろんのこと，津波ハザード評価において強震動による海岸・河岸構造物の脆弱性の影響は無視できないことを示している．

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

地表震度や液状化等のハザードマップは，等価線形解析または非線形の全応力解析がなされているとはいえ，本質は，N値とせん断波速度Vsの経験式に基づく鉛直一次元弾性計算によるものが中心である．表層地盤は強震時，本来弾塑性近似すべきであり，しかも不整形な地層・基盤構造による表面波生成などの多次元効果なしには，地震動の振幅増大と長周期化，継続時間増大が求められず，現行一次元解析は地震被害を過小評価する危険性がある．本稿は，多層地盤の多次元弾塑性地震応答解析により，不整形境界における実体波の屈折と，そこから生成・伝播した表面波と実体波の複雑な干渉が，表層の地震被害を局所的・非均質的に甚大化することを示す．

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

本研究では，スマートフォンとインターネットGISを組み合わせた，リアルタイム災害情報収集システムを開発した．行政と民間企業，住民が災害初動期において情報共有することで，情報収集にかかる人的資源の不足を補うことを目的としている．2016年熊本地震の災害調査や，多数地域での訓練を通じて，システムの有効性を確認することができた．他方，自治体と民間企業など，異なる立場の組織が協力して情報収集を行うような枠組みを社会実装する上では，システム開発の範疇にとどまらない様々な課題があることも判明した．

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス   Country：Japan  

著者らはこれまでに，砂質土のサイクリックモビリティなども表現可能な複合負荷弾塑性構成式を開発してきた．本発表では，同構成式が砂に限らず，粘土の単調および繰返し挙動も再現可能であることを速報的に示す．

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス   Country：Japan  

横ずれ断層が変位すると，その直上に堆積した表層地盤内にはフラワー構造と呼ばれる花弁状のすべり面が複合的に形成され，地表面には「ミの字型」で規則的に並ぶ亀裂群であるリーデルせん断帯が出現することが知られている．著者らはこれまでに，断層変位場を境界条件として与えた表層地盤の弾塑性有限変形解析において「ジョグ」の存在を考慮することで，特徴的な付随断層構造の生成過程が再現できることを示してきた．本稿では，ジョグの幾何形状を系統的に変更した解析の結果を紹介するとともに，フラワー構造の生成過程についても議論する．

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス   Country：Japan  

地盤内部は起伏に富んだ地層構成を形成しているため，地震時の波動伝播は複雑となる．調査結果によると，堆積盆地内で揺れが局所的に大きくなり，地震被害が甚大化した事例が報告されているが，これは堆積層内での加速度増幅に加え，盆地端部の不整形基盤から生成された表面波の伝播や実体波と表面波の複雑な干渉が影響していると考えられる．本報では，軟弱な粘性土が堆積する堆積盆地を対象に多次元地震応答解析を実施し，地層不整形性が表層地盤被害へ及ぼす影響を検討する．

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス   Country：Japan  

飽和土の水～土骨格連成解析の支配方程式は， u-p formulation と呼ばれる体系に基づいて定式化されることが多い．ところが，このu-p formulation は，方程式系を単純化する過程で「間隙水の静的浸透」を仮定する手法であり，動的浸透も生じうる高透水性土に適用すれば計算は破綻する．そこで著者らは，もとの支配方程式を上述の静的浸透の仮定なしでそのまま解くFull-formulationのうち，u-w-p formulation に基づく連成有限変形解析手法を新たに開発してきた．本稿では，まずu-p formulation の限界について示し，次いでFull-formulationを動的問題に適用することで，この限界を克服できることを示す．

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス   Country：Japan  

飽和土の変形を記述する水～土骨格連成計算においては，「間隙水の静的浸透」を仮定するu-p formulationに基づく定式化がしばしば採用される．u-p formulation の適用により，支配方程式中の未知数を削減し，計算負荷を大幅に抑えることが可能となる．ところが，高透水性の多孔質媒体中では間隙水は動的にも運動しうるため，間隙水の加速度を無視して強引に解こうとすれば，連成計算は破綻してしまう．そこで著者らは，上述の仮定を導入することなく支配方程式を直接解くFull-formulation1)のうち，u-w-p formulation に基づく連成有限変形解析手法を新たに開発してきた．本稿では，本手法を低透水性土～高透水性土～超高透水性土の圧密問題に適用した結果について考察する．

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

A seepage model test of a river levee on the ground having a highly permeable soil layer was simulated
using a soil-water-air coupled finite deformation analysis code incorporating the SYS Cam-clay model
which can describe suction effect. The simulated result showed that the levee body became normal
consolidation state due to decease in suction effect associated with increase in saturation degree and
thereby slip failure of the levee body could occur. In addition, the soil element on the slip surface showed
softening behavior with plastic volume expansion.

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

平成24 年7 月の九州北部豪雨による矢部川堤防の被災は，局所的なパイピングをきっかけとして決壊した「越流なき破堤」として大きな衝撃を与え，複雑な地盤条件・水理条件においても合理的に河川堤防の安全性照査が可能な最新の地盤力学に基づく解析手法の構築が求められている．本稿では，粘土から砂，さらにはその中間土までの力学挙動を統一的な枠組みで記述可能な弾塑性構成式
SYS Cam-clay モデルを搭載した空気～水～土骨格連成有限変形解析コードを用いて，透水模型実験のシミュレーションを行い，浸透破壊する場合としない場合の違いを表現できることを示した（解析コードのValidation）．また，本解析コードを用いたケーススタディも実施して，基礎地盤と堤体の土質や境界／外力条件の違いが，浸透破壊発生の有無に与える影響を示した．

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

バーチカルドレーンの排水効果を近似的に水～土連成解析に取り入れる手法としてマクロエレメント法と呼ばれる一種の均質化法がある．著者らはウェルレジスタンス現象の発生を合理的に扱えるよう，同手法にドレーンの排水機能を付加するなどして機能拡張を図った．本稿では，高機能化したマクロエレメント法の準静的問題における近似精度について検証した．この結果，著者らが高機能化を図ったマクロエレメント法は，計算コストを大幅に削減しつつ，複数本のドレーンを有する大規模でかつ盛土載荷を併用した真空圧密工法のように複雑な載荷履歴を受ける問題においても高い近似精度を発揮することが明らかになった．なお，同手法は動的問題においても高い近似精度を発揮する．

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

本稿では，push-upおよびpull-apartを模擬した不連続な断層変位場（幾何学的初期不整）を境界条件として考慮した3 次元弾塑性有限変形解析を実施することで，横ずれ断層における局所的なjogの存在に起因した付随断層構造の形成プロセスを数値解析的に再現することを目指す．この結果、横ずれ断層におけるjog（幾何学的初期不整）を境界条件として考慮した弾塑性有限変形解析により，fractalなRiedel せん断やP-shear，低角・高角なせん断面といった特徴的な付随断層構造の形成過程を再現できた．

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

従来の地震時被害／対策では砂質地盤の液状化現象が注目されることが多いが，メチオカン地震(1895)やトルコ地震(1999)など，軟弱粘土地盤が関与したと考えられる地震中～地震後被害も数多く報告され，近年研究も鋭意進められてきている．しかし，粘土地盤の実務・研究の多くは人工的な練返し正規圧密粘土を対象にした構成式が用いられており，骨格構造が発達した自然堆積地盤の動的挙動を把握するには十分と言えない．名古屋大学では土の骨格構造（構造，過圧密，異方性）とその働きを記述した弾塑性構成式（SYS カムクレイモデル）を提案している．本報では，繰返し載荷による軟弱粘土の乱れの影響を非排水三軸圧縮試験結果から把握するとともに，上記構成式の応答と対比することで，軟弱粘土の動的挙動の把握には構造概念が重要であることを示した．

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Records observed in bedrocks have been used to extrapolate seismic origin model. However, if non-linear response occurred in the surface ground, the influence of it on the records would not be negligible. In addition, multi-dimensional wave propagation can occur because most deposited grounds are neither horizontal nor even. Therefore, this study proposed a new estimation method for the incident wave to base rock from an observational record while taking into account non-linearity response of surface ground such as liquefaction phenomena and multi-dimensional wave propagation by using a soil-water coupled elasto-plastic finite deformation analysis code. In other words, through this achievement, a new utilization of the viscous boundary condition (VBC) will be proposed. In addition, the feasibility of the proposed method will be examined.

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

A slip on strike-slip fault causes flower structures and Riedel shear bands within the overlying cover. In our former research, the Riedel shear bands formation process was simulated considering the material
imperfection in ground by utilizing the three-dimensional elasto-plastic finite deformation analysis code GEOASIA. On the other hand, it's known that the existence of jog (geometrical barrier) has an important
role on the formation process. This paper simulates a strike-slip faulting process considering jog as a
geometrical imperfection in ground on the strike-slip fault. As a result, the formation processes unique to
subsidiary fault such as fractal shear bands, P-shear, low and high angle shears appeared.

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

In the 2011 off the Pacific coast of Tohoku Earthquake, extensive liquefaction damages were observed over a wide range of reclaimed coastal land. It is reported that, in Chiba prefecture, the big aftershock occurred 29 minutes after the main shock and it caused expanding the liquefaction damage. In this paper, using a soil-water-air coupled finite deformation analysis code incorporating the elasto-plastic constitutive equation 'SYS Cam-clay model,' it showed that groundwater level rise due to main shock expands liquefaction damage during aftershock.

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Earthquake motions include waves of various frequency bands ranging from low to high frequency. Notably,
the difference in dominant frequencies affects the seismic stability of fill slopes. Hence, to analyze the
deformation/failure mechanism during an earthquake, 1G shaking-table tests were conducted on saturated fill
slopes considering the resonance phenomenon. Evaluating the seismic stability of the fill slopes depends on not only the magnitude of the acceleration but also the relationship between the natural frequency and the input frequency. Moreover, it is also important to grasp the change in the natural frequency associated with the progress of plastic deformation due to repeated loading.

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Most of the existing damage prediction methods not only do not substantially take account of the nonlinearity of the ground but also are based on one-dimensional vertical evaluations. Therefore, multi-dimensional effects due to an irregular stratigraphic and bedrock structure are not taken into consideration. In this paper, two-dimensional elasto-plastic effective stress analysis is carried out noticing the irregularity of the ground stratification. As a result, complex interference between the surface waves and body waves provides not only inhomogeneous deformation but also localized and extensive damage at the ground surface.

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学川内北キャンパス   Country：Japan  

著者らはこれまでに，側圧一定の不飽和シルト三軸試験の数値シミュレーションを行い，弾塑性構成式SYS Cam-clay modelを搭載した空気～水～土骨格連成有限変形解析コードを用いれば，一組の材料定数と初期値により，サクション付与・等方圧密過程およびその後の様々な排水・排気条件下におけるせん断試験結果を概ね再現できることを示した．その一方で，吸水コラプス挙動のように，土骨格の構成式にサクションの効果を考慮しなければ表現できない挙動に関しても確認を行った．本稿では，SYS Cam-clay model に，不飽和化に伴い限界状態線の切片を上昇させるZhang and Ikariyaによる比較的簡単な手法を用いてサクションの効果を導入し，サクション付与・等方圧密過程，およびその後の排気排水，非排気非排水三軸圧縮試験の数値シミュレーションを行った．

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学川内北キャンパス   Country：Japan  

東日本大震災では，浦安市をはじめとして，東京湾沿岸部の埋立地盤において広範囲に液状化被害が発生した．千葉県では本震に加えて29 分後に大きな余震が襲い，余震時に噴砂などの液状化被害が拡大したことが報告されている．本稿は，弾塑性構成式SYS Cam-clay modelを搭載した空気～水～土骨格連成有限変形解析コードを用いて，余震時に液状化被害が拡大し得ることを，地盤の地下水位が地震により上昇する点に注目して示す．

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学川内北キャンパス   Country：Japan  

南海トラフ巨大地震に備え，既設の防波堤の地震時の変状を予測するとともに，変状に応じた対策が求められている．本報では，愛知県内にある防波堤を対象に地震応答解析を実施し，防波堤の耐震性や地震後の機能維持について検討を行った．解析コードは，砂から中間土，粘土までを同じ理論的枠組で記述する弾塑性構成式（SYS カムクレイモデル）を搭載した水～土骨格連成有限変形解析コードGEOASIAである．

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学川内北キャンパス   Country：Japan  

N値ゼロの軟弱層を持つ地盤上に設置された岸壁構造物の耐震性を、2次元および3 次元の水～土連成有限変形解析により照査し、両者の結果を比較考察した。

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.5 - 2016.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

In the simulation of the vertical drain method using a soil-water couple finite element analysis, macro-element method can be used as an approximate method to introduce the water absorption and discharge functions of drains into individual elements. Although this method has been applied only to quasi-static problems, the author extends the function of the method and applied it to the soil-water coupled analysis code GEOASIA with inertial term to grasp the countermeasure effect of the excess pore water pressure dissipation method against liquefaction. In this paper, in order to verify the new macro-element method in dynamic problem under plane strain condition, the results of 2-dimentional analysis using the new macro-element method was compared with those of 3-dimentional analysis in which vertical drains were expressed exactly by dividing finite element meshes finely.

Event date： 2016.5 - 2016.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

A soil-water-air coupled finite deformation analysis of a seepage model test was conducted. In the model test, a sand layer with relatively higher permeability is covered with another sand layer with relatively lower permeability directly below the river levee. The analysis can well simulate time and place of the boiling phenomena, which shows the validation of the analysis. Furthermore, from the case studies, it is found that both the difference of the permeability between the layers and the head difference affect the occurrence of boiling and the deformation/failure patterns.

Event date： 2016.5 - 2016.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Soil-water coupled finite deformation analysis has usually been based on u-p formulation, whose set of equations is reduced by assuming 'the relative acceleration of the fluid phase with respect to the solid phase is sufficiently smaller than the acceleration of the solid phase.' In response to the exponential progress of high-performance computation, we developed a sophisticated soil-water coupled finite deformation analysis code on the basis of full-formulation incorporating the exact equations without the assumption. The paper reveals that Full formulation-based code can conduct soil-water coupled analysis takeing dynamic flow of pore water among the saturated soil into consideration.

Event date： 2016.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：English   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 豊中キャンパス（大阪府豊中市待兼山町）   Country：Japan  

Event date： 2014.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学ES館   Country：Japan  

Event date： 2014.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学ES館   Country：Japan  

Event date： 2014.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学ES館   Country：Japan  

Event date： 2014.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場ほか   Country：Japan  

Event date： 2014.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場ほか   Country：Japan  

Event date： 2014.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場ほか   Country：Japan  

Event date： 2014.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場ほか   Country：Japan