Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

The present paper investigates a 3-D numerical analysis method, combining peridynamics (PD) and the discrete element method (DEM), which can simultaneously handle both the fracture and post-fracture behavior of materials assumed to be soils. With geomaterials, it is very important to treat the process from fracture to post-fracture in a continuous manner. The bond-based PD model is employed to reproduce the behavior from the initiation of cracks to fracturing. At the same time, the DEM model is also introduced so that the contact forces among the fragmented pieces can be calculated after the fracturing. The computational process of the physical contact between the wall element and the computational nodes of the PD is also solved based on the DEM so that plane geometry boundaries can be used. For the failure criteria of the connection between the computational nodes of the PD, a bilinear type of bond model is introduced to obtain a nonlinear stress–strain relationship and numerical stability when the calculation process switches from PD to the DEM. To verify the proposed approach, numerical simulations of the diametral compression test are performed on flawless cylindrical specimens, and the results are compared with theoretical solutions for the stress distribution inside the specimens. Based on the results, a simulation of the compressive failure of multiple soil-like crushable objects is performed as an example of the application of the coupled PD-DEM. The obtained results show that the proposed method will serve as a computational framework that can treat the continuous fracture behavior of soil-like materials in three dimensions.

DOI： 10.1016/j.compgeo.2023.105372

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

For the estimation of the ultimate bearing capacity (UBC) of footings, most contemporary formulas employ a linear yield function in the shear stress-normal stress space. However, it is well known that the general property in the failure envelopes of sandy soils manifests the non-linear effect of the stress level on the peak friction angle. The focus of this research study is the assessment of the UBC of surface strip footings ascribed to the effect of confining stress level and relative density (Dr) on the shear strength of sandy soils. The rigid plastic finite element method (RPFEM), using the confining stress dependence property of Toyoura sand, is utilized in non-linear finite element analyses. The results of the UBC analyses are ascertained to be consistent with those of the centrifuge experiments in the published references. The ground failure domains in the case of the non-linear shear strength model are gleaned smaller than those in the case of the linear shear strength one. The analysis results are compared with prevailing guidelines, for instance, the Architectural Institute of Japan (AIJ) and the Japan Road Association (JRA), which are developed for the mean shear strength property of sandy soils. The applicability of the UBC formula to effective stress analysis is also discussed, and the modified formula is developed

DOI： 10.21660/2023.102.g12171

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Publishing type：Research paper (scientific journal)   Publisher：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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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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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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Part of collection (book)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (international conference proceedings)  

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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Publishing type：Research paper (international conference proceedings)  

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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Language：Japanese   Publisher：Japan Society of Civil Engineers  

Similarities of hydraulic model experiments for river including seepage flow through saturated porous riverbed materials, are investigated here based on the governing equations of numerical model. With the theoretical and computational results, it is shown that more attention should be paid to keeping consistency with Froude number similarity. 1/N Scaled physical roughness heights of river bed are required to satisfy Froude similarity for river flow, 1/N scaled groundsill and grain size are required to satisfy Shields number similarity for bed load, 1/1 or 1/√N scaled permeability is required to satisfy partial similarity or Froude similarity as river flow. The similarities at boundary roughness and grain size will be lost due to a too small scale 1/N. and, a 1/1 scaled permeability under small scale 1/N experiment may lead the river flow reduces due to relative bigger seepage flow.

DOI： 10.2208/jscejam.76.2_i_411

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Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：土木学会  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：International Society of Geotechnical Engineering  

In the Kashiwazaki Plain, Japan, wide-area subsidence occurred after the 2007 Niigata-ken Chuetsu-Oki earthquake. The stratified ground subsidence meter clearly exhibits the thick clayey layer had caused subsidence after the earthquake. The measurement data of leveling at various points gives the spatial distribution and the time-dependent property of subsidence. By analyzing the instantaneous and the long-term amounts of subsidence at each point from the observed data, this paper reports the correlation with geology and topography and discusses the cause for subsidence of clayey soils after the earthquake.

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

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

In order to evaluate the flow filed and the stability of the groundsill, numerical simulations were performed for fixed bed hydraulic model experiments of river consolidation works with a hydraulic drop. The numerical results are in good agreement with experimental data. Numerical results show that forces acted on the blocks get maximum value at the hydraulic jump, while groundsill failure is observed here in experiments. The computations also show that pore water pressure decreases with increasing permeability of materials under the structure, increases with seamlessly connecting the groundsill blocks.

DOI： 10.2208/jscejam.75.2_i_519

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Publishing type：Research paper (scientific journal)  

The slaking of geomaterials often causes some unexpected geohazards, such as slope failures, debris flows, rockfalls, and so on. In particular, the process of slaking is highly enhanced when the geomaterials include swelling clay minerals such as montmorillonite and saponite. In order to investigate the mechanisms of the slaking phenomenon from a microscopic point of view, this study presents a particle simulation model based on the discrete element method (DEM) that can reproduce the slaking process of geomaterials that include swelling clay minerals. The properties of swelling and shrinking are modeled by changing the diameter of the DEM particles which are assumed to comprise the swelling clay minerals and several sand particles. A series of simulations of the deformation of mudstone under a wet-dry cyclic condition is performed in both two and three dimensions. As a result of the analyses, the applicability of the proposed model to the slaking phenomenon is confirmed.

DOI： 10.21660/2019.54.8230

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

Fixed bed hydraulic model experiments were carried out for a gentle slope block type groundsill with a flexible structure. Numerical simulations were also performed to obtain the seepage flow included velocity field and the pressure field around the groundsill. The numerical and experimental results show a good agreement. It is shown that vertical hydrodynamic forces acting on the blocks have local maximum value and the pressure varies periodically at the hydraulic jump. The computations also show that pore water pressure increases with decreasing permeability of materials under the structure, decreases at the gap of the groundsill blocks. In scoured hole, bottom velocity of submerged hydraulic jump is several times bigger than the value of undular hydraulic jump’s reverse velocity.

DOI： 10.11532/river.25.0_451

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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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Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：土木学会  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Taylor & Francis Group  

This study presents a 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 (DE) method and the Lattice Boltzmann (LB) method are employed for the soil particles and for the seepage flow, respectively. On the basis of the coupled DE-LB 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. 2-D and 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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Nagaoka University of Technology  

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

A calibration procedure is proposed to determine the angle of internal friction and the coefficient of rolling friction between the particles for the Discrete Element Method (DEM) simulation from a direct shear test using glass beads. To examine the accuracy of DEM computation, hourglass simulation under different local damping, in addition to these identified parameters, is compared with the PIV measurement of corresponding experiment. It is revealed from the comparison that there remain some difficulties in simulating the overall behavior of the experiment by tuning local damping.

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The stability of river-bed structures near water drop works, standing against river flow forces is important due to the increase of river discharge according to global warming. The stability is affected not only by the river flow forces but also seepage flows and seepage pressures. Especially sucking out of fine soil grain due to seepage pressures diminishes foundation strength.

In this study, we developed hydraulic and geotechnical modelling to evaluate stability of foundation around water drop works. Numerical modelling and Laboratory experiment facility were set up for the 1st year of the studies.

DOI： 10.11532/river.24.0_655

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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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Publisher：土木学会  

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Language：English   Publishing type：Research paper (other academic)   Publisher：Internal Association for Computer Methods and Advances in Geomechanics  

This paper estimated the ultimate lateral resistances of piles for both the pile group (2x2) and the square footing against horizontal ground movement by using two-dimensional rigid plastic finite element method (RPFEM). The effect of pile spacing on ultimate lateral resistance of two models was investigated through case studies. The obtained results showed that the ultimate resistance of pile in pile group tended to coincide with that of isolated single pile when the pile spacing is large. However, it decreased with the decrease in pile spacing and the total lateral resistance of pile group was found to approach to that of square footing. The effect of pile spacing on load apportionment ratio of pile was studiously investigated. Moreover, this study focused the group effect on ultimate lateral resistance of piles in line alignment of 1x2 and 1x3 by taking account of pile spacing, through case studies.

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Language：English   Publishing type：Research paper (other academic)   Publisher：Internal Association for Computer Methods and Advances in Geomechanics  

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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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Language：Japanese   Publisher：Japan Society of Civil Engineers  

A 3D particle-fluid coupled model was applied to concentrated leak erosion, which one of the mechanisms to trigger internal soil erosion. The method is based on a coupling the Discrete element method (DEM) and the Lattice Boltzmann method (LBM). The motion and collision of solid particles were calculated by the DEM, and the fluid flow of the pore fluid was directly solved at a lower particle scale by the LBM. By coupling these methods, the interaction between the particle and the fluid could be also calculated. In order to verify the particle-fluid coupled method, small 3D models were simulated based on the Hole Erosion Test (HET). Soil erosion parameters (such as critical shear stress and erosion rate) are calculated and compared with the results available in the literature. Consequently, this study facilitates more realistic simulations, compared with the available tests and 2D numerical simulations in the literature.

DOI： 10.2208/jscejam.73.i_429

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

We proposed a direct numerical simulation model of seepage flow and granular soils by combining the lattice Boltzmann method and the discrete element method. Multiple Relaxation Time (MRT) model was introduced in order to obtain stable solutions of the fluid flow under high Reynolds number condition. Partially Saturated (PS) model, which retain 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.

DOI： 10.2208/jscejam.72.I_335

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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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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The failure of earth dams is mainly caused due to internal erosion and piping phenomena. Concentrated leak erosion, one of the mechanisms to trigger internal erosion, is driven by flow in the cracks or other openings. In the present study, an effort has been made to investigate the microscopic coupled behavior of soil skeleton and water by employing the Discrete Element and Lattice Boltzmann coupled method. Many simulations were conducted under different constant pressure conditions with 2-D small model based on Hole Erosion Test presented by Wan and Fell (2004). Soil erosion parameters (such as, hole diameter φ_t, shear stress τ_t, erosion rate ε) are calculated and compared with the results available in the literature. Consequently, this study facilitates more realistic simulations compare to the available tests and simulations in the literature.

DOI： 10.2208/jscejam.71.I_567

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

A simple model for the Discrete Element Method (DEM) with fewer parameters is proposed so that boundary value problems in geotechnical engineering can be studied. The interparticle contact bond model, which reproduces the behavior of cohesive geomaterials, and the rolling friction model, which 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 DEM parameters and the failure criteria for geomaterials by means of c and ϕ

DOI： 10.2208/jscejam.67.105

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Language：Japanese   Publisher：National Committee for IUTAM  

Seepage force at the surface of the sand matrix or ground becomes important for considering the phenomena, such as sediment transport or erosion. This article presents the microscopic computation of the seepage force in the sand matrix by the lattice Boltzmann method, and compares the magnitude of the force at in the sand matrix with that at its surface. The numerical results have revealed that the superficial/interfacial seepage force is slightly smaller than the interior seepage force when the seepage water flows through a uniformly packed sand matrix.

DOI： 10.11345/japannctam.66.0_69

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Language：Japanese   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

The maintenance of damaged irrigation tunnels has become a major social concern; and thus, evaluating the damage conditions of current tunnels is of crucial importance. Voids behind the tunnel lining may be created during or after construction by the conventional method, and these voids are the main factors in its failure. Hence, it is imperative to comprehend the behaviors of the ground, the tunnel lining and the voids. This paper presents model tests of the interacting behaviors between the ground and a tunnel lining with voids under loading conditions. The experimental results show that the longitudinal and lateral convergences are large in the case of a void of 90 degree angle. To investigate the local deformation and the damage pattern, the three-dimensional distinct element method is applied, incorporating the Concrete Particle Model, and the numerical results are compared with the experimental data. The comparison clarifies the qualitative evaluation of the deformation behavior of the tunnel in the model tests by the numerical method.

DOI： 10.11408/jsidre.88.i_105

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Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I030577228

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

Movable block hydraulic model experiments were carried out for a gentle slope block type groundsill. VOF and Darcy Law based numerical simulations were also performed to obtain the seepage flow and river flow simultaneously. Hydrodynamic forces acting on the movable blocks, pressures at the upper and bottom surfaces of blocks, are measured and calculated in both experiments and simulations. The numerical results show good agreement with experimental data. Dynamic stabilities based on fluid forces acting on block and frictional force between block and riverbed, are then evaluated numerically. it is shown that lifts acting on blocks are bigger and should not be estimated by using lift coefficient and velocity at close upstream of hydraulic jump, due to upwelling seepage flow. The computations also show drag acting on end block may be several times bigger than that acting on others.

DOI： 10.11532/river.26.0_401

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

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