記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.compgeo.2023.105372

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掲載種別：論文集(書籍)内論文  

It is proven that the sandy soils exhibit the non-linear trend in the shear stress- normal stress space. This study discusses the assessment of the UBC of surface strip footing on sandy soils concerning size effect and relative density subjected to centric vertical and uniform surcharge loads. The RPFEM, based on the shear strength property of Toyoura sand, is employed in analyses. The findings are consonant with the centrifuge tests in the published references. The results are compared with the existing guidelines, and the modified UBC formula is proposed.

DOI： 10.1201/9781003299127-192

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.21660/2023.102.g12171

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

In geotechnical engineering, the stability of strip footings under eccentrically inclined coupled loads is a major concern. The objective of this paper was to estimate the ultimate bearing capacity of a rigid strip footing, subjected to eccentrically inclined loads resting on cohesive-frictional soil, using the rigid plastic finite element method (RPFEM). In the numerical analysis, an interface element was introduced to properly evaluate the interaction between the footing base and the soil. The footing base was assumed to be rigid and rough, as it most often is in reality. Focus was placed on the effect of the soil properties (cohesive strength c, internal friction angle ϕ, and unit self-weight γ) and footing width B on the loading planes of the V-H-M limit load space (vertical load-horizontal load-moment) in order to consider the uniqueness of this limit load space. In particular, the effect of the two directions of the horizontal load, namely, positive and negative horizontal loads, on the V-H-M limit load space was clarified. The numerical results of the RPFEM showed that the negative horizontal load had a positive effect on supporting a higher bearing capacity than the positive horizontal load in the presence of a small eccentricity length. However, the results also showed a negligible effect on the bearing capacity for both directions of the horizontal load in the presence of a large eccentricity length. New equations were proposed to determine the V-H-M limit load space, predicted as functions of c/γB and ϕ, by taking into account the direction of the horizontal load. The applicability of the V-H-M limit load space was widely examined for several loading paths with different prescribed loads for V, H, and M. Consequently, the limit load space of the strip footing was clearly found to be unique for each value of c/γB and ϕ.

DOI： 10.1016/j.compgeo.2022.104956

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掲載種別：研究論文（学術雑誌）  

This study investigated the effect of different water contents (w) and initial crack lengths on the mechanical properties (i.e., the unconfined compressive strength (UCS), deformation modulus, and mode II fracture toughness (KIIC)) and failure modes of pre-cracked compacted clay under uniaxial compression. In this study, 44 intact specimens and 72 pre-cracked specimens with different water contents (18%, 23%, and 28%) and initial crack lengths (0, 15 and 20 mm at 45°, i.e., the angle at which the maximum shear stress acts on the initial crack surface). The results showed that the UCS decreased with a long initial crack or high-water content. In contrast, the deformation modulus depends on water contents, but not on the initial crack length. KIIC was calculated. It was found to depend on the water content. Empirical correlation formulas between KIIC vs. w and KIIC vs. UCS were obtained. Furthermore, the failure modes of the compacted clay were classified into five types. In some specimens, wing cracks propagating from the initial crack disappeared due to contact and gliding of the crack surface by the shear stress, and only secondary cracks were observed at failure.

DOI： 10.1016/j.enggeo.2022.106593

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掲載種別：研究論文（学術雑誌）  

Wide-area land subsidence occurred across the Kashiwazaki Plain, Niigata, Japan after the 2007 Niigata-ken Chuetsu-Oki Earthquake. The stratified ground subsidence meter clearly showed that a thick clayey layer had caused this subsidence after the earthquake. To examine the ground conditions, a boring survey was conducted at the site and the physical and mechanical properties of the ground were tested. Although leveling surveys are insufficient for surveying the behavior of the ground, the measurement data obtained at various points from these surveys are meritorious for grasping the spatial distribution and the time-dependent property of the land subsidence. In this study, by analyzing the instantaneous and the long-term amounts of land subsidence at each point from the time-series observation data, the correlation between geology and topography is reported and the cause of the land subsidence of the clayey soils after the earthquake is discussed. It is clarified that the existence of a marine clay layer greatly affected the long-term subsidence of the land.

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Lecture Notes in Civil Engineering  

This study presents a 3-D particle simulation model based on the discrete element method for the weathering processes of geomaterials. We modeled their properties of swelling and shrinking by changing the diameter of spherical region which is consisting of clay minerals and several sand particles. A series of simulations of deformation of mudstone under wet-dry cyclic condition was performed so that the applicability of the proposed model can be validated.

DOI： 10.1007/978-3-030-64514-4_64

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

The accuracy of the pore-scale intergranular flow analysis by the lattice Boltzmann method (LBM), with the aid of the discrete element method (DEM), is investigated and compared with the experimental results of saturated seepage flows. Due to its simplicity and computational efficiency, a regularized Bhatnagar-Gross-Krook model is employed for the LBM to increase the numerical stability. After examining the performance of the numerical method by two well-known problems, namely the Hagen-Poiseuille flow and the flow past a stationary single sphere, a pore-scale numerical simulation of the saturated seepage flow is conducted. Permeability tests are carried out with an artificial porous medium prepared by a 3D printer, consisting of a sufficient number of resin particles. The experimental results are compared with those of the LBM numerical simulation, in which the pore structure of the porous medium is reproduced by the DEM. The numerical results are seen to have properly predicted the macroscopic properties obtained by the permeability tests, which have shown the prominent applicability of the LBM-DEM analysis to pore-scale intergranular fluid flows.

DOI： 10.1007/s11440-021-01210-z

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

The present paper reports the application of a 2-D coupled fluid-particle simulation model with no macroscopic assumptions to the seepage failure of saturated granular soils. The basic problem of the seepage failure of a horizontal ground with an embedded sheet pile, where the system size is set to be 200 × 100 mm and the average diameter of the soil particle is 550 μm, is numerically investigated. Both the seepage flow and the motion of the soil particles are directly solved by coupling the lattice Boltzmann method and the discrete element method. The goal of this study is to confirm that the 2-D direct simulation can be performed on the scale of a model experiment with soil particles that correspond in size to that of real sand. As a result of the analysis, it is shown that a typical series of behavior for seepage failure, where boiling and heaving initially occur on the downstream side near the sheet pile and finally lead to quicksand, can be seamlessly reproduced. Comparing the cases with different initial void ratios, it is found that the deformation area and the rates of the failure process can be varied according to the packing state. By tracking the velocity of each soil particle, it is visually shown that seepage failure begins to occur in the corner areas of the sheet pile much earlier than the onset of quicksand. By focusing on the fluid force acting on that particle, it is seen that the relatively large values for the hydrodynamic forces are concentrated on the upstream side before the beginning of uplift. In addition, by a comparison with two theories for the critical hydraulic gradient, the current limitations and problems of the proposed method are also summarized.

DOI： 10.1016/j.compgeo.2021.104234

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掲載種別：論文集(書籍)内論文   出版者・発行元：Springer International Publishing  

This study estimated on the bearing capacity of a footing against eccentric vertical load placed on two types of soil, namely, sandy soil and clayey soil, using the rigid finite element method (RPFEM). For the sandy soil, the study newly introduces an interface element into the footing-soil system to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. For the clayey soil, the study improves the analysis procedure by introducing a zero-tension analysis into the footing-soil system. Two friction conditions of the footing surface were considered which are a perfectly rough and smooth conditions. The effect of the eccentric vertical load on the normal stress distribution at the footing base and the failure envelope in V-M plane is thoroughly investigated. According to the obtained results, it can be seen that changes in the normal stress distribution reflecting to both the eccentricity length and the friction condition were observed. Finally, new equations were proposed to determine the normalized V/Vult and the failure envelopes of both sand and clay.

DOI： 10.1007/978-3-030-64518-2_10

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Lecture Notes in Civil Engineering  

The experimental investigations of seepage force on interfacial bed particles furnish only macroscopic phenomenological characteristics. Microscopic numerical analyses provide effective alternative tools to assess the hydraulic and deformation characteristics of cohesionless granular soils of seepage domain in a coupled fashion. The present study reports the application of a 3-D direct particle–fluid simulation model for seepage force on interfacial bed particles of cohesionless granular soils. The seepage force acting on particles comprising the uppermost layer of cohesionless granular soils bed is studied numerically from the micromechanical aspects without macroscopic assumptions. The particle scale calculations are modeled by a soft sphere model, such as the Discrete Element Method (DEM), and the flow of the pore fluid is directly solved at a smaller scale than the diameter of the soil particles by the Lattice Boltzmann Method (LBM). The interaction between the soil particles and the seepage flow is also considered by coupling these methods. A number of series of analyses until critical hydraulic gradient are accomplished. The result shows that the numerically predicted value for the seepage force coefficient of particles near the surface is reduced regardless of the hydraulic gradient. However, the numerical result is not in good agreement with the experimental result reported in (Martin and Aral 1971).

DOI： 10.1007/978-3-030-64518-2_38

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

浸透流と跳水を含む河川流を同時に計算する数値モデルの基礎方程式に基づいて，浸透流を含む河川の水理模型実験の相似性について調べた．理論的誘導と計算結果が，フルード相似を適用する河川の模型実験において河床壁面条件，河床粒径と河床材透水係数の相似に注意を払うべきと示した．1)河川流のフル ード相似を満たすのに長さ縮尺 1/N に従った河床の壁面相似が必要，2)掃流砂のシールズ相似を満たすのに縮尺 1/N に従った河床粒径が必要，3)浸透流の相似を満たすのに縮尺 1/1 または 1/√N に従った透水係数の相似が必要である．但し，縮尺が小さすぎると 1)の壁面相似と 2)の掃流相似が失われ，3)の縮尺 1/1 に従った透水係数は，透水係数が大きい模型実験の場合に浸透流の相対的な増大により河川流が影響される事態を招く．

DOI： 10.2208/jscejam.76.2_i_411

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Lecture Notes in Civil Engineering  

This study estimated the bearing capacity of footing against eccentric vertical load on sandy soils by using two-dimensional rigid plastic finite element method (RPFEM). The study newly introduces an interface element into the footing-soil system to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. Two friction conditions of the footing surface were considered, namely, a perfectly rough and smooth conditions. The effect of the eccentric vertical load on the contact stress distribution at the footing base and the failure envelope in V-M plane is thoroughly investigated. According to the obtained results, it can be seen that changes in the contact stress distribution reflecting to both the eccentricity length and the friction condition were observed. Finally, the new equation is proposed for the failure envelope through the comparison with those found in the literature.

DOI： 10.1007/978-981-15-2184-3_148

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

In geotechnical engineering, the stability of rigid footings under eccentrically inclined loads is an important issue. This is because the number of superstructures has increased and the situation of structures being subjected to eccentrically inclined loading is occurring more and more frequently. The objective of this paper was to evaluate the bearing capacity of a rigid footing on the free surface of uniform sandy and clayey soils under the action of eccentric and inclined loading using a finite element analysis by assuming that the soils follow the Drucker-Prager yield function. In the two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) was applied to calculate the ultimate bearing capacity of the eccentric-inclined loaded footing. In the numerical analysis, an interface element was introduced to simulate the footing-soil system with the rigid plastic constitutive equation developed by the authors. The footing was considered to be rigid and rough, as it most often is in reality. This study thoroughly considered the effect of the soil properties on load inclination factors iγ and ic in order to investigate the validity of the current design methods. In particular, the effects of the horizontal load in two directions on the ultimate bearing capacity of the footing and the failure envelopes in the V-H-M space were clarified, namely, positive and negative horizontal loads. The results showed that the positive horizontal load had a negative effect on the bearing capacity, while the negative horizontal load had the opposite effect in the presence of eccentrically inclined loading. The failure mode of the footing-soil system was clearly seen in the difference between the two directions of horizontal load. Through a series of numerical analyses, new equations were proposed for load inclination factors iγ and ic, and for the failure envelopes in the V-H-M space, taking into account the direction of the horizontal load. The obtained limit load space was proved to be rational in comparison to those given in the literature. Furthermore, the applicability of the limit load space to different loading paths, and moreover, to the independently prescribed loads of V, H, and M, was examined. Consequently, the failure envelope for each type of soil in the V-H-M space was clearly seen to be unique.

DOI： 10.1016/j.sandf.2020.05.004

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掲載種別：研究論文（国際会議プロシーディングス）  

In the 2011 Great East Japan Earthquake, many caisson type seawalls were damaged by the tsunami. The stability assessment of seawalls against tsunami is a current important issue in earthquake engineering. This paper applied the rigid plastic finite element method to the stability assessment of seawalls by taking account of seepage force in the mound which supported the seawalls. The applicability of the analysis method was systematically verified through the comparison with the centrifuge model tests conducted by the Port and Airport Research Institute. The applicability of conventional design method was also discussed through case studies.

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掲載種別：研究論文（国際会議プロシーディングス）  

This study presents an improvement in coupled particle-fluid numerical simulation model for the internal erosion of granular soils with a broad particle size distribution in order to investigate the mechanisms of the motion of fine soil particles inside the matrix of coarse soil particles from a microscopic point of view. In the model, the discrete element method (DEM) and the lattice Boltzmann method (LBM) are employed for the soil particles and for the seepage flow, respectively. On the basis of the coupled DEM-LBM model, two types of coupling schemes are newly combined. The coarse soil particles are simulated by the microscale-coupled method where the fluid flow is modeled at smaller scales than the soil particle diameter, while the fine soil particles are simulated by the macroscale-coupled method where the fluid flow is modeled at larger scales than the soil particle diameter. 3-D simulations of suffusion are performed, and the applicability of the proposed model to the internal erosion of granular soils is validated.

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：土木学会  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：International Society of Geotechnical Engineering  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

In earthquake engineering, pile foundations are designed to withstand the lateral loading that results from large displacements due to ground movement caused by strong earthquakes. The distress and failure of superstructures occurs when the lateral load exceeds the ultimate lateral resistance of the piles. The aim of this study is to estimate the ultimate lateral resistance of piles especially in terms of the group effect induced by the pile arrangement. Several experimental and numerical analyses have been conducted on pile groups to investigate the group effect when the groups are subjected to uniform large horizontal ground movement. However, the ultimate lateral resistance of the pile groups in these studies was calculated by applying load to the piles. The present study directly assesses the ultimate lateral resistance of pile groups against ground movement by systematically varying the direction of the ground movement. Although the load bearing ratio of each pile in a pile group, defined as the ratio of the ultimate lateral resistance of each pile in a pile group to that of a single pile, is an important design criterion, it was difficult to assess in past works. This study focuses on the load bearing ratio of each pile against ground movement in various directions. The use of the finite element method (FEM) provides options for simulating the pile-soil system with complex pile arrangements by taking the complicated geometry of the problem into account. The ultimate lateral resistance is examined here for pile groups consisting of a 2 × 2 arrangement of four piles, as well as two piles, three piles, four piles, and an infinite number of piles arranged in a row through case studies in which the pile spacing is changed by applying the two-dimensional rigid plastic finite element method (RPFEM). The RPFEM was extended in this work to calculate not only the total ultimate lateral resistance of pile groups, but also the load bearing ratio of the piles in the group. The obtained results indicate that the load bearing ratio generally increases with an increase in pile spacing and converges to almost unity at a pile spacing ratio of 3.0 with respect to the pile diameter. Moreover, the group effect was further investigated by considering the failure mode of the ground around the piles.

DOI： 10.1016/j.sandf.2018.08.013

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Lecture Notes in Civil Engineering  

This study estimated the ultimate lateral resistance of pile group against horizontal ground movement by using two-dimensional rigid plastic finite element method (RPFEM). The effect of ground movement direction on the ultimate lateral resistance was investigated through the case studies. According to the results, it can be seen that changes in both the ultimate lateral resistance and the failure mode of ground around piles were observed. The effect of the pile spacing on load apportionment ratios was studiously investigated. Since each pile in the group affects other piles, it leads the load apportionment ratio significantly to depend on pile positions such as the front or back piles. Moreover, the load apportionment ratio of each pile went up with an increase in pile spacing, but it was obtained different remarkably among piles. The load apportionment ratio varied with the direction of the ground movement.

DOI： 10.1007/978-981-13-2306-5_57

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記述言語：日本語   出版者・発行元：日本学術会議 「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」  

落差床止め工まわりの流れ場とその安定性を解明するために，落差床止め工の固定床模型実験に対する数値計算を行った．数値計算の結果は模型実験によく一致している．数値実験の有効性が確認されてから，様々な条件の下で計算を行い，流れ場の特性と構造物の安定性を考察した．計算結果は，構造物の下に透水性の良い敷砂利があると揚圧が下がり，逆に構造物間の隙間がないと揚圧が上がることを示した．また，跳水位置で床止め工ブロックの受ける流体力が極大になり，跳水位置でブロックの破壊が始まる実験の観察に一致する．止水矢板の有無と配置位置の流れ場および構造物安定性への影響も調べられた．

DOI： 10.2208/jscejam.75.2_i_519

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掲載種別：研究論文（学術雑誌）  

DOI： 10.21660/2019.54.8230

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

DOI： 10.11532/river.25.0_451

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掲載種別：研究論文（学術雑誌）  

In geotechnical engineering, the stability of rigid footings under eccentric vertical loads is an important issue. This is because the number of superstructure buildings has increased and the situation of structures being subjected to eccentric vertical loading is occurring more and more frequently. In this study, focus is placed on the ultimate bearing capacity of a footing against the eccentric load placed on two types of soil, namely, sandy soil and clayey soil, using a finite element analysis. For the sandy soil, the study newly introduces an interface element into the footing-soil system in order to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. For the clayey soil, the study improves the analysis procedure by introducing a zero-tension analysis into the footing-soil system. Two friction conditions between the footing and the soils are considered; one models a perfectly rough condition and the other models a perfectly smooth condition. For a two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) is applied to calculate the ultimate bearing capacity of the eccentrically loaded footing. The RPFEM is extended in this work to calculate not only the ultimate bearing capacity, but also the distribution of contact stress along the footing base. The study thoroughly investigates the effect of the eccentric vertical load on the ultimate bearing capacity in the normalized form of V/Vult and e/B where e is the length of the eccentricity and B is the width of the footing. Vult indicates the ultimate bearing capacity of the centric vertical load. The failure envelope in the plane of V/Vult and M/BVult is further investigated under various conditions for the sandy and clayey soils. M is the moment load induced by the eccentric vertical load. This study examines the applicability of the failure envelope obtained for the eccentric vertical load to the cases where two variables, V and M, are independently prescribed. The obtained results are coincident and indicate the wide applicability of the failure envelope in the normalized V-M plane in practice. Finally, in a comparison with previous researches, the numerical data in the present study lead to the derivation of new equations for the failure envelopes of both sandy and clayey soils.

DOI： 10.1016/j.sandf.2019.09.004

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：土木学会  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Taylor & Francis Group  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Nagaoka University of Technology  

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

Sliding of natural and artificial slopes generally occurs during or following strong earthquakes. Such sliding is greatly affected by a combination of geological conditions and earthquake loading. Earthquake-induced landslides often cause more damage to infrastructure and human lives than the earthquake itself. Pseudo-static analysis is widely implemented as one of several design methods used in engineering practice to assess the seismic stability of natural and artificial slopes. However, the most important issue of pseudo-static analysis is to select the most appropriate method for measuring seismic coefficient. In order to investigate this, back analysis was conducted for surficial slides subjected to strong ground motion during the 2004 Mid-Niigata prefecture earthquake in Japan. This paper surveyed the stochastic properties of earthquake-induced surficial slides and clearly showed that the obtained results were applicable to back analysis of shear strength and seismic coefficient. In back analysis, soil properties such as soil strength and density and sliding depth were assumed as random variables owing to their uncertainties. Seismic coefficient is also assumed to be a random variable and varies with distance from the epicenter fault line. The analysis of 4504 recorded surficial slides clearly shows a unique relationship of landslide occurrence ratio with slope angle and distance from the epicenter fault line. This study’s results enhance the calculation of the shear strength of weathered soil covering slopes and the horizontal seismic coefficient through back analysis procedure. By considering possible stochastic properties of variables, some case studies were implemented in the back analysis.

DOI： 10.1007/s10346-018-1029-6

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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：京都大学学際融合教育研究推進センター高大接続科学教育ユニット  

土の挙動を粒子レベルから数値的にシミュレートすることには, 幅広い需要と応用性があり, 本研究では, 2次元砂時計を流れ落ちる砂の挙動を粒子レベルからモデリングすることを試みた. まず, ガラスビーズを実験試料とし, 一面せん断試験から材料の摩擦特性を計測した後, 2 次元砂時計装置でのガラスビーズの流下挙動をPIV計測を通して観測した. 個別要素法による数値シミュレーションでは, 一面せん断試験の結果から, ガラスビーズの粒子間摩擦角と転がり摩擦係数を求め, 減衰係数を調整することで2次元砂時計実験の再現を試みた. 実験と数値解析では定性的な一致を得たものの, 一面せん断試験から得られた粒子間摩擦角と転がり摩擦係数を固定した上で, 減衰係数のみ変えて砂時計内を流れ落ちるガラスビーズの形状変化を正確に再現することは困難であった.

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

DOI： 10.11532/river.24.0_655

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掲載種別：研究論文（学術雑誌）  

The paper reports the application of a 3-D direct particle–fluid simulation model to the seepage failure of granular soils. The goal of this study is to numerically capture the process of the failure which is induced by the seepage flow from the micromechanical aspects with no macroscopic assumptions. In order to accomplish this goal, non-cohesive granular assemblies with an upward seepage flow and a variety of pressure gradients are investigated. The motion and the collision of the soil particles are calculated by a soft sphere model, such as the discrete element method, and the flow of the pore fluid is directly solved at a smaller scale than the diameter of the soil particles by the lattice Boltzmann method. By coupling these methods, the interaction between the soil particles and the seepage flow is also considered. As a result of the series of analyses, the numerically predicted value for the critical hydraulic gradient is found to be in good agreement with the theoretical value. In addition, the rapid change in the flow pattern around the critical hydraulic gradient can be microscopically captured. By observing the evolution of the force chains inside the soils, it is demonstrated that the failure process of the contact networks can also be reproduced by the simulation model presented here.

DOI： 10.1007/s40571-017-0180-5

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出版者・発行元：土木学会  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）   出版者・発行元：Internal Association for Computer Methods and Advances in Geomechanics  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）   出版者・発行元：Internal Association for Computer Methods and Advances in Geomechanics  

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掲載種別：研究論文（学術雑誌）  

This paper reports a comparison of two types of sheared granular soil specimens, with almost the same void ratios but considerably different fabric, using the discrete element method in two dimensions. The specimens are prepared by applying two different methods of particle generation; one specimen is generated by placing the particles geometrically, while the other specimen is generated by placing the particles randomly. Then, computational direct shear tests are conducted in order to compare the yielding behaviours of the two specimens. The obtained bulk shear responses show different trends, even though the values for the void ratio at the initial state are almost the same. Toward the critical state, however, the initial differences in the stress state and the granular fabric gradually disappear and eventually reach almost the same state. The results reveal that not only macroscopic quantities, but also the contact force distribution and the angular variation in contact forces, have a unique critical state. In particular, the angular distribution of contact angles inside the shear band is also found to have a unique critical state.

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

内部侵食は観測が困難である土中で進行するため，問題の解決には数値計算が有用な手法となる．本研究では浸透流による水みちの拡大過程に焦点を当て，浸透流と土粒子の両方をLattice Boltzmann MethodとDiscrete Element Methodを連成させて直接解いた．粒子間の固着モデルを導入することで，粘性土の粘着特性を表現し，土粒子間の固着力を表すパラメータと土試料に作用する両端の圧力差を変えながら，繰り返しの検討を行った．その結果，土粒子間の固着力に大きさに応じて，土粒子集合体としての侵食に対する抵抗力の大きさが変化することを表すことができ，従来の2次元での応用例より再現性が高まることが確認できた．

DOI： 10.2208/jscejam.73.i_429

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

浸透流を伴う土のマイクロメカニクスを調べるために，浸透流と土粒子の両方をLattice Boltzmann Method（LBM）とDiscrete Element Method（DEM）を連成させて効率良く直接解くことが出来る数値計算手法について検討した．まずは，浸透流の計算に対する数値安定性を高めるために，Multiple Relaxation Timeモデル（MRTモデル）を導入した．また，3次元で土粒子の大きさ以下の解像度で浸透流を扱う場合は必然的に計算コストが高まるため，LBMの並列性の高さを損なわないような連成モデルとしてPartially Saturatedモデル（PSモデル）を選択した．そして，これらを新たに組み合わせたPS-MRT Lattice Boltzmannモデルの妥当性と地盤工学への適用性について検証した．

DOI： 10.2208/jscejam.72.I_335

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掲載種別：研究論文（国際会議プロシーディングス）  

The shape effect of the blocks comprising a dry-stone masonry retaining wall under seismic loading was investigated through numerical simulations using the three-dimensional discrete element method. The variations in block shape, namely, cubic-shaped and wedge-shaped, were compared. For the numerical simulations, the seismic resistivity was higher in the wall of wedge-shaped blocks than in the wall of cuboid blocks, although the total mass was larger for the wall of cuboid blocks. These results are good agreement with the centrifuge model tests. Furthermore, a detailed investigation was performed by the discrete element model to explore the mechanism of the shape effect.We found that the surface area, which contributes to the frictional resistance between each stone block and the backfill, is the key parameter to mobilizing the anti-seismic strength of a dry-stone masonry retaining wall. © 2015 Taylor & Francis Group, London.

DOI： 10.1201/b17435-284

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

土壌の内部侵食は観察が難しい現象であるため，数値シミュレーションによって現象の理解と予測をすることが有用となる．本研究では浸透流によるConcentrated leak erosionに焦点を当て，固体粒子の計算手法であるDEM（個別要素法）と流体の計算手法であるLBM（格子ボルツマン法）を組み合わせ，土と水のミクロな挙動を同時に解いた．Wan and FellのHET（Hole Erosion Test）を参考にした二次元モデルを作成し，浸透流を発生させて粒子の流出を観察した．勾配を変えながら繰り返し計算を行い，侵食に関する各パラメータを算出して既往の実験やHETを模擬したシミュレーションとの比較・検討を行った．固体粒子の取り扱いに関して新たな条件を導入したことで，従来に比べてより実験に近いシミュレーションを行うことができた．

DOI： 10.2208/jscejam.71.I_567

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：INT CENTER NUMERICAL METHODS ENGINEERING  

We proposed a direct numerical simulation model of granular soils and seepage flow by combining the discrete element method and the lattice Boltzmann method. The MRT model was introduced in order to obtain stable solutions of fluid flow under high Reynolds number condition. The PS model, which retains a local operation at each fluid node and keep from intensive increasing the computational costs for the calculation of collision term, was also introduced as a solid-fluid coupled model. We show the effectiveness of the PS-MRT lattice Boltzmann model through several validation tests.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPANESE GEOTECHNICAL SOC  

The shape effect of the blocks comprising a dry-stone masonry retaining wall under seismic loading was investigated through centrifuge model tests and numerical simulations using the three-dimensional discrete element method. Variations in block shape, namely, cubic-shaped and wedge-shaped, were compared. For both the physical experiments and the numerical simulations, seismic resistivity was higher in the wall of wedge-shaped blocks than in the wall of cuboid blocks, although the total mass was larger for the wall of cuboid blocks. Therefore, a detailed investigation was performed by the discrete element model to explore the mechanism of the shape effect. We found that the surface area, which contributes to the frictional resistance between each stone block and the backfill, is the key parameter to mobilizing the anti-seismic strength of a dry-stone masonry retaining wall. (C) 2014 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sandf.2014.11.007

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

In order to study the effects of the rolling friction of the particles on granular packing, we present a detailed analysis of circular disk assemblies with the rolling friction under macroscopic one-dimensional compression. The rolling friction of the particles produces a resisting moment to the rolling at each contact. A series of 2-D DEM simulations are performed with various values for the rolling friction parameter. We focus on several macroscopic and microstructural properties of granular media and analyze them as a functions of the rolling friction. From these results, we show that the rolling resistance, which results from the rolling friction of the particles, contributes to the inhibition of the rearrangement of the particles and increases the magnitude of the fabric anisotropy under packing. In addition, from both microscopic and macroscopic points of view, we describe that the stress state in a granular packing can vary considerably depending on the rolling resistance.

DOI： 10.1007/s10035-013-0398-8

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掲載種別：研究論文（国際会議プロシーディングス）  

A simple model for the Discrete Element Method (DEM) is proposed so that boundary value problems in geotechnical engineering may be studied using DEM with fewer parameters. The interparticle contact bond model, which was suggested by Utili and Nova and reproduces the behavior of cohesive geomaterials, and the rolling friction model, which was suggested by Sakaguchi et al. and expresses the interlocking effect of grain shapes with circular particles, are introduced into the conventional contact model for the two-dimensional DEM. Both of these models require only one parameter. Parametric analyses, based on several direct shear tests, are performed to validate the proposed model and to obtain relationships between the failure criteria for geomaterials (c and w) and the corresponding micromechanical quantities.

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Society of Civil Engineers  

土木分野で扱う大規模な境界値問題を個別要素法（以下，DEM）で解析することを念頭に，より少ないパラメータで地盤特性を適切に表現できるシンプルなDEMモデルを提案した．具体的には，地盤材料の破壊基準である粘着力と内部摩擦角を表現するために，通常の円形粒子のDEMで用いられる粒子接触関係に粒子間ボンドモデルと転がり摩擦モデルにそれぞれ修正を加えたものを導入した．両モデルを導入する際に必要とする追加パラメータはそれぞれ1つだけである．これらのモデルを反映させたDEMを用いて一面せん断シミュレーションでのパラメトリックスタディを行い，地盤材料の粘着力と内部摩擦角に対して所望の値を適切に表現するためのモデルとパラメータ決定方法を与えた．

DOI： 10.2208/jscejam.67.105

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記述言語：日本語   出版者・発行元：日本学術会議 「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」  

砂の表面に作用する浸透力の評価は、土砂輸送や土の侵食を力学的な観点から考える上で重要となる。ここでは、格子ボルツマン法を利用し、砂の粒子で構成される間隙を流れる浸透流をシミュレートすることで、砂（砂塊）の内部と表面の浸透力を数値的に計算する。その結果は，均一な粒形を持つ砂を想定した場合、表面の浸透力は内部のそれよりも小さくなることを示した。

DOI： 10.11345/japannctam.66.0_69

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記述言語：日本語   出版者・発行元：公益社団法人 農業農村工学会  

老朽化した農業用水路トンネルの維持管理は社会的な懸案事項となっており，現時点でのトンネル変状の正確な把握が重要である．矢板工法で施工されたトンネルでは，施工中・施工後にトンネル覆工に背面空洞が発生することが多く，この空洞により劣化が進展する．そのため地山と背面空洞を有する覆工の挙動の正確な理解が必要である．本論文では，地山に背面空洞を有するトンネルを想定したモデルを用い模型実験により相互挙動を確認した．載荷実験では，背面空洞が90°の場合に，縦方向と横方向の内空変位量が大きくなることが明らかになった．また，変形挙動やひび割れ性状を検討するため，構成式にConcrete Particle Modelを用いた三次元の個別要素法により解析を行い，実験結果との比較を行った．比較検討により，本解析手法がトンネルの模型実験の変状を定性的に評価できることが明らかとなった．

DOI： 10.11408/jsidre.88.i_105

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その他リンク： https://ndlsearch.ndl.go.jp/books/R000000004-I030577228

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

DOI： 10.11532/river.26.0_401

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記述言語：日本語   掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）  

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記述言語：日本語   掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）  

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記述言語：日本語   掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）  

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記述言語：日本語   掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：京都大学学際融合教育研究推進センター高大接続科学教育ユニット  

砂柱の崩壊は，砂粒子が大きく移動することで，砂柱が大変形する，最も基本的な砂の破壊現象の一つである．本研究では，砂柱の崩壊現象を実験・観察し，砂粒子の動きを一粒毎に計算できるDEM（Discrete Element Method）（1, 2） を用いてこの現象を数値的に解析した．実験では，粒径が約1 mm のガラスビーズを実験材料とし，PIV（Particle Image Velocimetry）（3） 解析によって砂柱が崩壊するときの変位及び変形速度を得た．数値解析においては，粒子サイズを実験と合わせてパラメトリックスタディを行い，実験における砂柱崩壊の再現を試みた．その結果，砂柱崩壊現象のシミュレーションには，減衰係数が重要な役割を果たすことが明らかとなった． There is one crucial parameter that governs the simulation of sand column failure. Our goal was to identify the parameters for applicability of DEM (Discrete Element Method) to simulate the failure of sand columns, one of the most fundamental phenomena underlying sand failure. In this study, we conducted an experiment on the failure of sand columns. We chose glass beads that have a grain diameter of approximately 1 mm as the material for the experiment. We employed PIV (Particle Image Velocimetry) analysis to obtain the profile of displacement and the speed of transformation during the failure process. We have simulated the sand column failure process using DEM and tried to reproduce the deformation that we observed in our experiment. We made the particle size in our analysis the same as that in the experiment, and conducted a parametric study that involved changing parameters, such as the friction angle between particles, the damping coefficient, and rolling friction. Our results indicate that the damping coefficient plays a significant role in simulations of sand column failure.

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：農業農村工学会  

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