研究者詳細 - 野田　利弘

論文 - 野田　利弘

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Elastoplastic finite element simulation of domino fault formation associated with tilting of highly structured ground 査読有り国際誌

Yamada, E., Noda, T. and Asaoka, A.

SOILS AND FOUNDATIONS 64 巻 ( 5 ) 2024年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Soils and Foundations

Ground deformation on the Earth's surface layer is strongly affected by the nonlinearity of geomaterials. However, the formation process of such deformation has yet to be described in a unified manner based on mechanics. The present study focuses on the normal faults in a submarine ground with highly developed soil skeleton structures and attempts to reproduce the process of normal fault formation associated with the tilting of a horizontally deposited submarine ground using an elastoplastic finite element simulation. The simulation was conducted using the soil–water coupled finite deformation analysis code GEOASIA, which incorporates an elastoplastic constitutive equation of the soil skeleton based on the modified Cam-clay model and the soil skeleton structure concept. The key findings are as follows: 1) Normal faults are formed from the ground surface to depth as shear bands, where shear strain is localized while exhibiting softening behavior with plastic volume compression. 2) Multiple normal faults are almost equally spaced and parallel to each other, with the inter-fault blocks rotating backward. The morphology of normal faults formed by the tilting of the ground shows domino-style characteristics. 3) The degree of the soil skeleton structure influences the formation of normal faults. This study demonstrates that elastoplastic geomechanics can explain the formation process of ground deformation, which has usually been interpreted from the perspectives of geomorphology and geology.

DOI： 10.1016/j.sandf.2024.101475

Web of Science

Scopus

Soil-water-air coupled finite deformation analysis considering trapped air and continuous air phases 査読有り国際誌

Yoshikawa, T. and Noda, T.

SOILS AND FOUNDATIONS 64 巻 ( 5 ) 2024年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Soils and Foundations

Since the soil–water characteristic model relates the matric suction and the water content, it cannot describe changes in the water content when the suction is zero and constant, i.e., all the pore air is trapped air. To reasonably describe changes in the water content due to air entrapment and the compressibility of trapped air, this paper presents a deformation analysis method based on the mixture theory for a four-phase mixture consisting of the soil skeleton, capillary water, trapped air, and continuous air, in which the pore air phase is divided into trapped air and continuous air phases. Specifically, considering the mass conservation equation and the equation of motion for each phase of trapped air and continuous air, and considering the mass exchange between the trapped air and continuous air phases, governing equations were derived for the initial and boundary value problems of the four-phase mixture in a finite deformation field using a rate-type equation of motion. Two examples are provided to validate the new method. Firstly, experiments and analyses of soil water retention tests were conducted under multiple drying-wetting cycles. A comparison shows that, even if hysteresis is not considered in the relationship between the effective degree of saturation and suction, the new method can successfully describe the gradual decrease in the degree of saturation at a suction of 0 kPa with multiple drying-wetting cycles, indicating that the pore air gradually becomes trapped in the pore water, by modelling the mass exchange between the trapped air and continuous air phases. Secondly, analyses of an unexhausted and undrained triaxial compression test under zero suction were conducted, comparing the new and previous soil–water-air coupling methods. The results show that the new method, unlike the previous method, can successfully simulate the experimental result. This is because the new method is able to describe the compressibility of trapped air as the change in the capillary water degree of saturation, which is a novel state variable defined as the ratio of the volume of capillary water to the total volume of capillary water and trapped air. The new method contributes to the simplification of the soil–water characteristic model and enables evaluations of the soil deformation behavior due to the compressibility of trapped air, such as a countermeasure against liquefaction caused by unsaturation.

DOI： 10.1016/j.sandf.2024.101480

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Scopus

Tsunami hazard evaluation of river embankment structures incorporating their vulnerability to seismic strong motion 査読有り国際誌

Imai, K., Nakai, K., Hirai, T., Noda, T., Arai, N., Iwama, S., Iwase, H. and Baba, T

EARTHQUAKE SPECTRA 40 巻 ( 3 ) 頁： 2008 - 2037 2024年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earthquake Spectra

Development of coastal areas in Japan for various land uses since the 1960s has contributed to industrial upgrades and improved the efficiency of transportation networks. However, there are concerns about the vulnerability of developments on alluvial plains and reclaimed lands to geological events, like ground subsidence due to liquefaction during large earthquakes. Realistic assessment of earthquake and tsunami hazards and evaluation of possible countermeasures require accurate estimation of the amount of subsidence that can be expected from liquefaction at coastal and riverside sites supporting various structures. In this study, to evaluate the amount a river embankment structure might be expected to settle as a result of strong motion from an assumed Nankai Trough great earthquake, we conducted a numerical simulation using the soil–water coupled finite deformation analysis code GEOASIA. We then investigated the effect of the estimated embankment subsidence on tsunami inundation, which was simulated by using nonlinear shallow-water equations and a grid spacing as fine as 3.3 m. The influence of urban structures on the inundated area was taken into account by using a structure-embedded elevation model (SEM). The results showed that subsidence of river embankments and the collapse of parapet walls on top of them would increase both the depth and area of inundation caused by a tsunami triggered by a Nankai Trough scenario earthquake. Our findings underscore the importance of evaluating not only earthquake resistance but also vulnerability of coastal and riverside structures to strong motion in tsunami hazard analyses. Furthermore, the importance of tsunami inundation analysis using a SEM for predicting the behavior of tsunami flotsam in urban areas was demonstrated.

DOI： 10.1177/87552930241237815

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Scopus

Super/sub-loading surface model for constitutive equation of friction 査読有り国際誌

Toyoda, T., Yasuike, R. and Noda, T.

TRIBOLOGY INTERNATIONAL 191 巻頁： 109080 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Tribology International

In this study, an elasto–plastic constitutive model of friction incorporating the superloading surface concept was formulated as an extension of the subloading friction model. The proposed model regards the state in which the static friction coefficient is larger than the kinetic friction coefficient as the “bulkiness” of structure and the smooth transition of friction was expressed by the evolution rule of structure.The positive definiteness of the plastic multiplier, the loading condition, and a condition equation for material parameters were clearly derived. The capability of the proposed model in accordance with the subloading-friction model was confirmed in the stick–slip simulation of a mass-spring system.

DOI： 10.1016/j.triboint.2023.109080

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Scopus

Comprehension of Seismic-Induced Groundwater Level Rise in Unsaturated Sandy Layer Based on Soil-Water-Air Coupled Finite Deformation Analysis 査読有り国際誌

Yoshikawa, T. and Noda, T.

WATER 16 巻 ( 3 ) 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Water (Switzerland)

Immense liquefaction damage was observed in the 2011 off the Pacific coast of Tohoku Earthquake. It was reported that, in Chiba Prefecture, Japan, the main shock oozed muddy water from the sandy ground and the aftershock which occurred 29 min after the main shock intensified the water spouting; thus, the aftershock expanded the liquefaction damage in the sandy ground. For comprehending such a phenomenon, using a soil–water–air coupled elastoplastic finite deformation analysis code, a rise in groundwater level induced by main shock is demonstrated, which may increase the potential of liquefaction damage during the aftershock. The authors wish to emphasize that these results cannot be obtained without soil–water–air coupled elastoplastic finite deformation analysis. This is because the rise in groundwater level is caused by the negative dilatancy behavior (plastic volume compression) of the saturated soil layer which supplies water to the upper unsaturated soil layer, and it is necessary to precisely calculate the settlement of ground and the amount of water drainage/absorption to investigate the groundwater level rise. This study provides insight into the mechanism of ground liquefaction during a series of earthquakes.

DOI： 10.3390/w16030452

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Unconditional convergence of theoretical solutions to u-p formulation 査読有り国際誌

Toyoda T. and Noda T.

Soils and Foundations 64 巻 ( 1 ) 頁： 101421 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Severe and nonuniform liquefaction damage of reclaimed ground contributed by interference between body waves and stratigraphic irregularity-induced surface waves 査読有り国際誌

Nakai, K., Noda, T. and Asaoka, A.

EARTHQUAKE SPECTRA 40 巻 ( 1 ) 頁： 287 - 313 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Experimental study on sand anisotropy using hollow cylinder apparatus 査読有り国際誌

Yamada, S., Okada, M., Nakano, M. and Noda, T.

SOILS AND FOUNDATIONS 63 巻 ( 3 ) 2023年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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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Finite-Deformation Cam-Clay Model Considering Elastic Dilatancy and Soil Skeleton Structure 査読有り国際誌

Yamada Shotaro and Noda Toshihiro

INTERNATIONAL JOURNAL OF GEOMECHANICS 23 巻 ( 2 ) 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

Web of Science

Verification of a Macroelement Method with Water Absorption and Discharge Functions in Quasi-Static Problems 査読有り国際誌

JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING 148 巻 ( 7 ) 2022年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Web of Science

Method to introduce the cementation effect into existing elastoplastic constitutive models for soils 査読有り国際誌

Journal of Geotechnical and Geoenvironmental Engineering 148 巻 ( 5 ) 頁： 04022013-1 - 04022013-14 2022年5月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

本震による傾斜を想定したガスホルダーの余震耐震性の簡易評価手法査読有り

小林実央，田附英幸，中井健太郎，野田利弘

土木学会論文集 A2(応用力学) 77 巻 ( 2 ) 頁： I_543 - I_550 2022年2月

担当区分：最終著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：土木学会

高度な安全性が要求される球形ガスホルダーは，大規模地震により基礎に不等沈下が生じた場合であっても余震時に供給機能を保持できることが望ましく，地震後の使用可否判断に資する，最大余震を想定した傾斜ガスホルダーの耐震性評価手法が必要である．その評価では支持構造部の材料・幾何学的非線形性や非線形ダンパーを考慮しなければならず，3 次元解析による詳細な評価は地震発生後短期間で実施することは現実的でない．このため本論文ではPushover解析から非線形ばね特性を反映した1 質点ばねモデル計算を用いた簡易な評価手法を提案した．本手法は，実機を対象にした3次元骨組モデルの動的応答との比較から最大応答値までは良い一致を示し，それ以降は安全側に応答値を算出するため，ホルダーの余震耐震性を評価できることを明らかにした．

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

Combined-loading elastoplastic constitutive model for a unified description of the mechanical behavior of the soil skeleton 査読有り国際誌

Yamada S., Noda T., Nakano M., Asaoka A.

Computers and Geotechnics 141 巻 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Effects of Strong Ground Motion with Identical Response Spectra and Different Duration on Pile Support Mechanism and Seismic Resistance of Spherical Gas Holders on Soft Ground 国際誌

Kobayashi Mio, Noda Toshihiro, Nakai Kentaro, Takaine Toshihiro, Asaoka Akira

APPLIED SCIENCES-BASEL 11 巻 ( 23 ) 2021年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：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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Numerical simulation based heuristic investigation of inertia-induced phenomena and theoretical solution based verification by the damped wave equation for the dynamic deformation of saturated soil based on the u-w-p governing equation 査読有り国際誌

Toyoda Tomohiro, Noda Toshihiro

61 巻 ( 2 ) 頁： 352 - 370 2021年4月

Importance of considering unsaturated triaxial tests including ceramic disk as initial and boundary value problems 査読有り国際誌

Yoshikawa, T., Noda, T. and Kodaka, T.

Soils and Foundations 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

浮き型格子状地盤改良による偏心荷重が作用した既設小規模構造物の液状化被害抑制効果査読有り

中谷一貴，森河由紀弘，中井健太郎，前田健一，野田利弘

土木学会論文集 A2(応用力学) 76 巻 ( 2 ) 頁： I_279 - I_288 2021年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）

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

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

PROGRESSIVE FAILURE OF UNSATURATED FILL SLOPE CAUSED BY CUMULATIVE DAMAGE UNDER SEEPAGE SURFACE 査読有り国際誌

Murao Hidehiko, Nakai Kentaro, Yoshikawa Takahiro, Noda Toshihiro

INTERNATIONAL JOURNAL OF GEOMATE 20 巻 ( 78 ) 頁： 1 - 8 2021年2月

担当区分：最終著者記述言語：日本語掲載種別：研究論文（学術雑誌）

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

Triaxial test on water absorption compression of unsaturated soil and its soil-water-air-coupled elastoplastic finite deformation analysis 査読有り国際誌

Yoshikawa Takahiro, Noda Toshihiro

SOILS AND FOUNDATIONS 60 巻 ( 5 ) 頁： 1151 - 1170 2020年10月

担当区分：最終著者記述言語：日本語掲載種別：研究論文（学術雑誌）

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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Seismic damage of soft clay layer directly under the river levee that becomes prominent by L2 earthquake 国際誌

Noda, T. and Nakai, K.

Proc. of the 17th World Conference on Earthquake Engineering (17WCEE) 頁： 4b-0040 2020年9月

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