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Semianalytical Solution for Earth Pressure of Narrow Granular Backfill with a Log-Spiral Failure Surface behind Retaining Walls under Translational Mode

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2023年第9期23卷 04023151-04023151页

作者： Li, Ming-Guang Chen, Hao-biao Chen, Jin-Jian Lin, Tong Shanghai Jiao Tong Univ Dept Civil Engn Shanghai Key Lab Digital Maintenance Bldg & Infras 800 Dongchuan Rd Shanghai 200240 Peoples R China

A novel semianalytical method is proposed to estimate the earth pressure exerted on rigid retaining walls supporting a narrow granular backfill in this study, which is based on the assumption of a log-spiral failure surface. This study adopts the differential element limit equilibrium method, coupled with the stress analysis considering the deflection of principal stress trajectory, to obtain the stress distribution against retaining walls. The resultant earth pressure, the point of application, and earth pressure distribution can be obtained by the finite-difference method. The method proposed in this study is verified via comparisons with model test results, centrifuge test results, and discrete-element method results. Furthermore, a series of extensive parameter studies are conducted to investigate the effect of backfill width and interface friction on resultant earth pressure, the point of application, and earth pressure distribution for further studies.

关键词： Narrow granular backfill Log-spiral failure surface Earth pressure Semianalytical solution discrete-element method

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Experimental Characterization and Computational Simulation of Powder Bed for Powder Bed Fusion Additive Manufacturing

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MATERIALS TRANSACTIONS 2022年第6期63卷 931-938页

作者： Kikuchi, Keiko Tanifuji, Yuta Zhou, Weiwei Nomura, Naoyuki Kawasaki, Akira Tohoku Univ Grad Sch Engn Dept Mat Proc Sendai Miyagi 9808579 Japan Powder Anal Co Tokorozawa Saitama 3590047 Japan

The packing density of powder bed is one of the critical parameters affecting the quality of the final parts fabricated via powder bed fusion additive manufacturing. In this study the packing density of the first layer of the powder bed was experimentally estimated from the packing densities of recoated powder with different number of layers. It is found that the packing density of the first layer is much lower than the apparent density of powder and the macro-scale packing density increases as the number of recoated layer increases. Furthermore, recoating simulation using discrete element method (DEM) was conducted to investigate the deposition mechanism of the powder at the particulate-scale. The simulation results showed the packing density of powder bed increases as the number of recoated layer increases, similar to the experimental results. This is caused by the rearrangement of the powder in the powder bed stimulated by the supplied powder. Also, the packing density of the powder bed was not uniform in the thickness direction, and the top surface layer which affects the quality of manufactured parts had almost the same packing density as that of the first recoated layer independently of the number of recoated layers.

关键词： additive manufacturing powder bed packing density discrete-element method

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Role of Material Fabric in Flexural Failure in Concrete

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JOURNAL OF ENGINEERING MECHANICS 2021年第12期147卷 04021112-04021112页

作者： Ghosh, Subha Deb, Arghya Indian Inst Technol Kharagpur Dept Civil Engn Kharagpur 721302 W Bengal India

A recently developed discrete-element capability was used to study the effect of mesogeometry on flexural failure in concrete. Fabric anisotropy in angular specimens was found to retard flexural crack growth. The fabric also played a key role in determining the geometry of the fracture process zone. Greater dispersion in the local fabric resulted in more tortuous cracks. Specimens with angular particles exhibited more crack branching and tortuosity, and hence had higher macrofracture energy, than specimens with rounded aggregates. Aggregate shape affected the peak stress and postpeak response of notched specimens. The slowing of crack growth and nonmonotonic evolution of the fracture process zone, also observed in experiments, was investigated. Crack tip shielding was found to play a critical role in explaining this behavior.

关键词： Material fabric Aggregate shape Maximum aggregate size discrete-element method Crack tortuosity Fracture process zone

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Effects of particle angularity on the bulk-characteristics of granular assemblies under plane strain condition

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COMPUTERS AND GEOTECHNICS 2023年 164卷

作者： Krengel, Dominik Chen, Jian Kikumoto, Mamoru Univ Tsukuba Dept Engn Mech & Energy 1-1-1 Tennodai Tsukuba 3058573 Japan Ctr Math Sci & Adv Technol Japan Agcy Marine Earth Sci & Technol 3173-25 Showa Machi Kanazawa-Ku Yokohama 2360001 Japan Yokohama Natl Univ Dept Civil Engn 79-5 Tokiwadai Hodogaya Yokohama Kanagawa 2408501 Japan

We investigate the influence of particle angularity on the stress-strain behaviour, rotation and micromechanics of granular assemblies under plane strain condition. Granular particles are modelled as regular polygons and numerical biaxial compression tests have been performed using the discrete element method. The packings consist of regular polygons with increasing corner number ranging from 5 to 64. The packings are analysed in the critical state in terms of their shear strength, bulk friction angle and porosity, as well as their cumulative rotation and contact characteristics with respect to varying particle angularity. We find that packings of more angular particles are looser but have higher shear strength, while packings of more rounded particles are denser, but are less resistant to shear. We further show that packings of angular particles are more resistant to reorganization by rotation, and that the mean rotation magnitude saturates at a constant value with increasing roundness. Lastly, we find that packings of more angular particles tend to have less contacts with higher normal and tangential forces when compared with packings of more rounded particles.

关键词： Shape effects Biaxial loading discrete-element method Soil strength

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Effect of Interparticle Friction on the Cyclic Behavior of Granular Materials Using 2D DEM

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JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING 2011年第5期137卷 545-549页

作者： Sazzad, Md Mahmud Suzuki, Kiichi Saitama Univ Dept Civil & Environm Engn Saitama 3388570 Japan

This study presents the influence of the interparticle friction angle on the cyclic behavior of granular materials using the two-dimensional (2D) discrete-element method (DEM). The numerical sample was modeled with oval-shaped particles, whereas the isotropically compressed dense sample was prepared from the initial sparse sample using periodic boundaries. Biaxial cyclic shear tests were simulated with different interparticle friction angles. It was noted that the width of the stress-strain cyclic loops becomes thin when the interparticle friction angle increases. It was also noted that the induced fabric anisotropy is more pronounced during unloading than loading. Moreover, a strong correlation between macro- and microquantities was observed for strong contacts during cyclic loading. DOI: 10.1061/(ASCE)GT.1943-5606.0000441. (c) 2011 American Society of Civil Engineers.

关键词： discrete-element method Interparticle friction Cyclic loading Anisotropy

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Aggregate Representation Approach in 3D discrete-element Modeling Supporting Adaptive Shape and Mass Property Fitting of Realistic Aggregates

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JOURNAL OF ENGINEERING MECHANICS 2020年第6期146卷 1-14页

作者： Jin, Can Li, Shouguo Yang, Xu Zhou, Xiaodong You, Zhanping Hefei Univ Technol Sch Automot & Traff Engn 193 Tunxi Rd Hefei 230009 Anhui Peoples R China Changan Univ Sch Highway Xian 710064 Peoples R China Michigan Technol Univ Dept Civil & Environm Engn 1400 Townsend Dr Houghton MI 49931 USA

Accurate representations of aggregates in stone-based materials are crucial to conducting reliable discrete-element (DE) simulations based on the microstructure of such materials. The objective of this study was to develop an adaptive representation method for aggregates to obtain corresponding clumps of spheres that closely fit realistic shapes and the inertia of the aggregates. Based on the developed three-dimensional (3D) solid model of each aggregate, the methodology consisted of three main steps, as follows: (1) the aggregate contour was displaced with surface spheres of different sizes in predefined fitting accuracy;(2) consequently, the internal space of the model was filled with inner spheres;and (3) eight spheres for inertia calibration were incorporated, with the sphere clump consisting of surface and inner spheres to generate the DE representation of the aggregate. DE representations of 11 aggregate particles were developed using the proposed method. Results imply that the obtained DE representation can occupy the volume of the aggregate more than 99.5% with a properly defined fitting accuracy and fit the aggregate in inertia very well. A numerical simulation of asphalt mixture compaction was conducted using the aggregate models generated in this study. The numerical simulation indicates that the aggregate models generated using the proposed method can be successfully used to generate stone-based materials such as asphalt mixtures.

关键词： Aggregate shape representation Microstructure discrete-element method Stone-based material

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Accelerated discrete-element Modeling of Asphalt-Based Materials with the Frequency-Temperature Superposition Principle

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JOURNAL OF ENGINEERING MECHANICS 2011年第5期137卷 355-365页

作者： Liu, Yu You, Zhanping Michigan Technol Univ Dept Civil & Environm Engn Houghton MI 49931 USA Michigan Technol Univ Transportat Mat Res Ctr Houghton MI 49931 USA Changan Univ Highway Sch S Erhuan Middle Sect Xian 710064 Peoples R China

This paper presents a methodology to reduce the computation time for discrete-element (DE) modeling of asphalt-based materials, based on the frequency-temperature superposition principle. Laboratory tests on the dynamic modulus of asphalt sand mastics and asphalt mixtures were conducted at temperatures of -5, 4, 13, and 21 degrees C and frequencies of 1, 5, 10, and 25 Hz, respectively. The test results of the asphalt sand mastics were fitted with the Burger's model to obtain the microparameters for DE models. To reduce the computation time of the DE modeling, the regular loading frequencies were amplified to virtual frequencies. Simultaneously, the Burger's model parameters (microparameters in DE models) of asphalt sand mastic at regular frequencies were modified to those at virtual frequencies on the basis of the frequency-temperature superposition principle. Because the virtual frequencies were much larger than the regular frequencies, the computation time was significantly reduced by conducting the DE modeling with the virtual frequencies and the corresponding modified Burger's model parameters. The modeling work, which typically takes several months or years with the traditional methods, only took a few hours or less in this study. DOI: 10.1061/(ASCE)EM.1943-7889.0000234. (C) 2011 American Society of Civil Engineers.

关键词： Asphalt mixes Viscoelastic discrete-element method Micromechanical modeling Burger's model Frequency-temperature superposition Reduce computation time

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Modeling Granular Materials: Century-Long Research across Scales

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JOURNAL OF ENGINEERING MECHANICS 2017年第4期143卷 1-20页

作者： Radjai, Farhang Roux, Jean-Noel Daouadji, Ali Univ Montpellier Lab Mecan & Genie Civil 163 Rue Auguste Broussonnet F-34090 Montpellier France MIT CNRS MIT Energy Initiat 77 Massachusetts Ave Cambridge MA 02139 USA Univ Paris Est Lab Navier 2 Allee Kepler F-77420 Champs Sur Marne France Univ Lyon INSA Lyon Lab SMS ID F-69621 Lyon France Inst Natl Sci Appl JCA Coulomb Lab Genie Civil Sols Mat Struct Integrite & Durab 34 Ave Arts F-69621 Villeurbanne France

Granular materials are the most recurrent form of solid-state matter on Earth. They challenge researchers and engineers in various fields not only because they occur with a broad variety of grain sizes, shapes and interactions in nature and industry, but also because they show a rich panoply of mechanical states. Despite this polymorphism, all these different types of soils, powders, granules, ores, pharmaceutical products, etc., are instances of the granular matter with the same least common denominator of being sandlike (psammoid in Greek), i.e.,solid grains interacting via frictional contacts. This review describes milestone contributions to the field of granular materials since the early elastic-plastic models developed for soils in the 1950s. The research on granular materials has grown into a vast multidisciplinary field in the 1980s with increasing focus on the microstructure and owing to new experimental tools and discrete simulation methods. It turns out that the granular texture, particle-scale kinematics, and force transmission are far more complex than presumed in early micromechanical models of granular materials. Hence, constitutive relations cannot easily be derived from the particle-scale behavior although advanced continuum models have been developed to account for anisotropy, intermediate stress, and complex loading paths. The subtle elastic properties and origins of bulk friction will be discussed, as well as the effects of particle shape and size distributions. The review covers also recent developments in macroscopic modeling such as the thermomechanical approach, anisotropic critical state theory, nonlocal modeling approach, inertial flows, and material instabilities. Finally, a brief account is given of open issues and some new frontiers and challenges in the field. (C) 2017 American Society of Civil Engineers.

关键词： Granular materials Constitutive modeling Micromechanics Fabric tensor Critical state theory Internal friction Dilatancy Force chains Jamming discrete-element method

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Particle-void fabric and effective stress reduction in cyclic liquefaction of granular soils

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SOIL DYNAMICS AND EARTHQUAKE ENGINEERING 2022年 153卷 107081-107081页

作者： Wei, Jiangtao Southwest Jiaotong Univ Sch Civil Engn Chengdu Peoples R China

During undrained cyclic loading, granular soils undergo the reduction of effective stress in the constant volume condition. Revealing the evolution of particle-void fabric in accompany with effective stress reduction provides a significant insight into the fundamental mechanism of cyclic liquefaction. In this study, numerical tests were conducted in DEM simulations to explore the cyclic liquefaction of granular packings with different particle size distributions and void ratios. With the decrease of mean effective stress p' during cyclic liquefaction process, the decrease of particle-void descriptor Ed can be observed for all packings. From micromechanical perspective, large size voids are redistributed and local void distribution around particle becomes relative uniform. The change of particle-void fabric from consolidated state to initial liquefaction state is irrelevant to density of the packing. A power function is further adopted to describe the positive correlation between Ed and p'.

关键词： discrete-element method Cyclic liquefaction Particle-void fabric

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Discontinuum Modeling of Solid Deformation Pore-Water Diffusion Coupling

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2017年第8期17卷 1-19页

作者： Cui, Yifei Chan, Dave Nouri, Alireza Univ Alberta Dept Civil & Environm Engn Edmonton AB T6G 2W2 Canada

This paper presents a numerical scheme for a solid-fluid coupled discrete-element method (DEM) that takes into consideration solid deformation and pore pressure generation and dissipation. Analytical solutions of conventional soil mechanics examples obtained by oedometer testing are used to quantitatively validate the proposed algorithm. The numerical results show good agreement with the analytical solutions. The proposed method advances the current capability of solid-fluid coupled DEM analysis to simulate the mechanical behavior of saturated granular materials.

关键词： discrete-element method Pore pressure dissipation Solid deformation pore pressure coupling

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