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Modeling of Asphalt Concrete Fracture Tests with the discrete-element method

JOURNAL OF MATERIALS IN CIVIL ENGINEERING 2020年第8期32卷

作者： Meza-Lopez, Juliana Norena, Nilthson Meza, Carlos Romanel, Celso Pontifical Catholic Univ Rio de Janeiro Dept Civil & Environm Engn BR-22451900 Rio De Janeiro Brazil

In this work, the discrete-element method was used to simulate crack propagation in asphalt concrete in two types of laboratory tests: the disk-shaped compact (DCT) test and the single-edge-notched beam (SEB) test with the three-point bending technique. The heterogeneous models were numerically simulated using the clump technique to represent the shapes of the aggregate, the particle size distribution, and the air voids in the asphalt concrete mixture. The overall mechanical behavior and the fracture propagation were simulated by the cohesive zone model, in the potential fracture area, and the viscoelastic Burger's model, in the remaining region of the samples. To obtain the values of the micro parameters required for the discrete-element model, a trial and error process was carried out comparing the mechanical behavior observed when considering the macro parameters of the asphalt concrete determined in laboratory tests. The numerical and experimental results are in good general agreement.

关键词： Asphalt concrete discrete-element method Crack propagation Cohesive zone Heterogeneous model

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Evaluation on Deformation Behavior of Granular Base Material during Repeated Load Triaxial Testing by discrete-element method

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第11期22卷 04022210-04022210页

作者： Li, Jue Zhang, Junhui Zhang, Anshun Peng, Junhui Chongqing Jiaotong Univ Coll Traff & Transportat Chongqing 400074 Peoples R China Changsha Univ Sci & Technol Key Lab Special Environm Rd Engn Hunan Prov Changsha 410114 Peoples R China Changsha Univ Sci & Technol Sch Traff & Transportat Engn Changsha 410114 Peoples R China

Granular base material (GBM) is widely used as the base/subbase course of pavement structure. In the mechanic-empirical design of flexible pavement, both the resilient modulus and permanent deformation are the major deformation properties of base materials, related to early-stage distresses of the surface layer under traffic loading. However, since the microscopic interaction between aggregates of the GBM is quite complex, the deformation behavior was not to be understood merely empirically. This study aims to evaluate the macroscopic and microscopic behavior of the GBM under repeated load triaxial (RLT) testing by the discrete-element method. Both the size gradation and the aggregate shape were considered in numerical simulations. The modeling technology of a heterogeneous structure was developed and verified by laboratory results. The results showed that the resilient modulus measured by the developed simulation was in good agreement with that of laboratory tests, within errors of 5.0%. The deformation behavior of the GBM presents the stress-hardening characteristic that the resilient modulus of the GBM increases from 94.03 to 337.71 MPa with the growth of the volume stress and deviator stress. The microstructure of the GBM maintain a relatively stabilization in dynamic response and anisotropy changes during the cyclic loading and voids within aggregates play a role in buffering the change in internal stress. The principal contact normal trends to the direction of maximum bulk stress through small motions, and rotations of aggregates during the loading. It provides a robust mechanism for the resistance to deformation, which results in dispersing more stresses into the skeleton.

关键词： Granular base material Repeated load triaxial test Deformation behavior discrete-element method Aggregate shape

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Geometrically exact discrete-element-method (DEM) simulation on the flow and mixing of sphero-cylinders in horizontal drums

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POWDER TECHNOLOGY 2018年 336卷 415-425页

作者： Yu, Fuhai Zhang, Shuai Zhou, Guangzheng Zhang, Yun Ge, Wei Chinese Acad Sci Inst Proc Engn State Key Lab Multiphase Complex Syst Beijing 100190 Peoples R China Univ Chinese Acad Sci Sch Chem & Chem Engn Beijing 100190 Peoples R China Tianjin Univ Sch Chem Engn & Technol Tianjin 300072 Peoples R China Collaborat Innovat Ctr Chem Sci & Engn Tianjin Tianjin 300072 Peoples R China

The mixing of non-spherical particles is often encountered in various industrial fields, but its mechanism is not well understood. Because of the complexity of contact detection for non-spherical particles, most simulations on particle mixing using the discrete-element method (DEM) are restricted to spherical particles. In this work, an efficient algorithm is used for the contact detection and the description of contact forces, with which the flow and mixing of geometrically exact sphero-cylinders in rotating drums was simulated in parallel computing using graphics processing units (GPUs). The specific shapes of the sphero-cylinders affect their dynamic behavior in mono- and bi-disperse systems, including the dynamic angle of repose, mixing constant, and segregation pattern. Certain kinds of preferential particle orientations exist, which are affected by the rotational speed and particle shape. The density difference leads to segregated cores of a higher density in the granular beds, whereas the effect of particle shape is secondary in this process. The joint effect of shape and density on particle distribution in the steady state can be used to improve the homogeneity of bi-disperse sphero-cylinder mixtures that differ in shape and density. (C) 2018 Elsevier B.V. All rights reserved.

关键词： discrete-element method Sphero-cylinder Mixing Rotating drum Shape effect

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Novel Approach for Generating Homogeneous Samples for discrete-element-method Studies

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第2期22卷

作者： Hu, Tiantian Tang, Yao Ling, Daosheng Wang, Xiukai Huang, Bo Zhejiang Univ Ctr Hypergrav Expt & Interdisciplinary Res MOE Key Lab Soft Soils & Geoenvironm Engn Hangzhou 310058 Peoples R China

A novel approach--the modified multilayer method--is proposed for generating homogeneous specimens for discrete-element-method (DEM) studies. The "particle boundary" is introduced at the interface between the layers, and the general servocontrolled technique is extended to the particle boundary to apply the stress field. Each layer of the specimen is compacted by moving the top and bottom boundaries simultaneously to generate the desired DEM specimen. Unlike existing methods, the proposed approach generates highly homogeneous specimens. The mechanism underpinning the new approach was determined by investigating the effect of the boundary movement on the final spatial distribution of the particles. A comparison with experimental direct-shear results shows that homogeneous samples generated using the proposed approach can accurately model the deformation and strength of granular material, whereas other methods lead to deviations due to sample inhomogeneity.

关键词： discrete-element method Sample preparation Particle boundary Servocontrolled technique

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Dynamic Performance of Wedge-Shaped Self-Leveling Sleepers in Railway Transition Zones

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2025年第2期25卷

作者： He, Xin Zhai, Wanming Guo, Yunlong Southwest Jiaotong Univ Train & Track Res Inst State Key Lab Rail Transit Vehicle Syst Chengdu 610031 Peoples R China Univ Birmingham Sch Engn Dept Civil Engn Birmingham B152TT England

Hanging sleepers, which result from the differential settlement of the ballast layer, are a prevalent issue that leads to the rapid degradation of track components that include the ballast, sleeper, fastener, and rail. A novel type of sleeper, the wedge-shaped self-leveling sleeper (WSS), was proposed as a solution to the hanging sleeper problem. The WSS leverages the train's dynamic loading and the gravity of the ballast to naturally allow the ballast particles to fill the gap between the ballast and the sleeper. This paper focuses on the dynamic performance of the WSS from different aspects, which include wedge angles (30 degrees, 45 degrees, and 60 degrees), sleeper materials (concrete and plastic), and the number of WSS to replace regular sleepers in the transition zone. A series of numerical modeling [which coupled multibody simulation (MBS) and discrete-element methods (DEM)] were conducted to design, optimize, and test the WSS. The results reveal that a concrete WSS is well-suited to address the problem of hanging sleepers in transition zones. The WSS with a 45 degrees angle demonstrated superior performance compared with other types of WSS. Importantly, the WSS could reduce vibrations in the vehicle and track, even when dealing with hanging sleepers. Due to the self-leveling function, the WSS shows significant promise for applications in transition zones, which could reduce the frequent need for track geometry maintenance.

关键词： Differential settlement discrete-element method discrete-element method-multibody simulation coupling Hanging sleepers Multibody simulation Railway transition zone Self-supporting sleeper Sleeper design

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Development of a Finite-Difference-discrete-element Coupled Model for Ram-Compacted Bearing Base Piles

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2025年第5期25卷

作者： Haris, Adhila El Naggar, Hany Shahin, Mohamed A. Bahrani, Navid Dalhousie Univ Nova Scotia Dept Civil & Resource Engn HALIFAX NS B3H 4R2 Canada Curtin Univ Sch Civil & Mech Engn Perth 6845 Australia

Ram-compacted bearing base (RBB) piles have been utilized as an effective foundation technique in China over the last 20 years. RBB is an enlarged technique for base piling that has proven to be a more economical and environmentally friendly solution than traditional piling methods. However, this technique remains unexplored in Western countries, and there have been only limited studies on the modeling and design of RBB piles. This paper discusses the development of three-dimensional (3D) numerical modeling of RBB piles by coupling the finite-difference method (FDM) and the discrete-element method (DEM). The explicit FDM program FLAC3D (version 7.0) was used to simulate the behavior of soil surrounding the pile wherein the material is represented by a number of continuum zones. The 3D DEM software Particle Flow Code (PFC3D7.0) was also used to simulate the flow and interaction of rubble particles through deformable contacts and time-domain solution of the equation of motion. The strengthened layer where the rubble base is constructed was simulated using a bonded particle model. The performance of the developed FDM-DEM model was then validated by comparing its results with site test results obtained from three case histories, and the outcomes were found to be in good agreement.

关键词： Ram-compacted bearing base (RBB) piles Numerical modeling Finite-difference method discrete-element method FLAC3D PFC3D

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discrete-element Numerical Investigation of the Dynamic Response Characteristics and Instability Mechanism of a Cross-Jointed Rock Mass Slope under Multistage Sustained Seismic Action

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2025年第2期25卷

作者： Song, Danqing Huang, Kunpeng Chen, Zhuo Zhang, Shuai South China Univ Technol Sch Civil Engn & Transportat State Key Lab Subtrop Bldg & Urban Sci Guangzhou 510640 Peoples R China Sichuan Agr Univ Coll Civil Engn Dujiangyan 611830 Peoples R China Tsinghua Univ Dept Hydraul Engn State Key Lab Hydrosci & Engn Beijing 100084 Peoples R China

Frequent earthquakes, coupled with discontinuous geological conditions, complicate the earthquake dynamic response characteristics of slopes. To reveal the dynamic accumulative damage effect and instability mechanism of a cross-jointed rock mass slope under continuous earthquakes, two discrete-element models, a homogeneous slope and a cross-jointed slope, are established in this study via particle flow code (PFC2D). The results show that the cross-jointed slope has an obvious dynamic amplifying effect on the elevation and slope surface. Compared with the homogeneous slope, the cross-jointed slope has a more significant slope magnification effect. The seismic wave amplification on cross-jointed slopes is more significant under the influence of S waves than P waves. In addition, on the basis of the characteristics of crack propagation and particle bonding failure, the dynamic cumulative failure effect and evolution process of cross-jointed slopes under cumulative earthquakes are revealed, including the crack initiation stage (<= 0.1g), crack accumulation stage (0.1-0.2g), crack propagation stage (0.2-0.4g), and crack penetration stage (0.4-0.6g). Through the analysis of particle bond rupture characteristics and displacement evolution, the mechanisms of dynamic failure and modes of instability for the cross-jointed slope are identified. Under a small earthquake (<= 0.2g), the slope remains largely uncracked, and slope failure does not occur. Under a strong earthquake (>= 0.4g), bond failure near the slope surface develops rapidly and intensively, and the sliding body gradually experiences instability failure. Moreover, joints control slope dynamic failure behavior. Shear failure and tensile failure mainly occur in cross-jointed slopes and homogeneous slopes, respectively.

关键词： Seismic response characteristics Cumulative failure evolution Cross-jointed slope Continuous earthquakes discrete-element method

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Optimal design of continuous integrated crystallization-filtration processes

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POWDER TECHNOLOGY 2025年 459卷

作者： Tan, Psalm Josiah Fang, Ming-Chun Lai, Bo-Zun Ward, Jeffrey D. Natl Taiwan Univ Dept Chem Engn Taipei 10617 Taiwan

Industrial crystallization is typically followed by filtration to separate the solid particles from the mother liquid and there is often a tradeoff between crystallizer and filter design: Investing more money in a larger crystallizer can increase crystal size and lower filtration costs. Thus, process simulation and optimization are essential to identify the optimal design of such integrated process. However such analyses are rare in the literature due to challenges in estimating cake resistance from a crystal size distribution (CSD). Recently it has been proposed to address this issue by combining the Kozeny-Carman equation with the discrete element method (DEM). In this work, this approach is applied to optimize continuous integrated crystallization-filtration processes including those where the CSD is modified by product classification or fines removal. Results show that the optimal design depends on crystallization kinetics and slurry viscosity. For systems with low nucleation rate and low slurry viscosity, the optimal design is to minimize the crystallizer cost. For systems with high nucleation rate and high viscosity, a rigorous process model is required to determine the optimal crystallizer volume and fines dissolver design.

关键词： Crystallizer design Filter design R-z crystallizer discrete-element method Economic analysis

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Numerical Study of the Failure Process of Stone Column Groups in Soft Soil in Response to Rigid Loading Based on the DEM-FDM Coupled Model

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2025年第4期25卷

作者： Tan, Xin Luo, Mengfei Yin, Xin Hu, Zhengbo Jin, Yuxuan Chen, Changfu Hunan Univ Coll Civil Engn Changsha 410082 Peoples R China Changsha Univ Sci & Technol Sch Traff & Transportat Engn Changsha 410014 Peoples R China Hunan Commun Res Inst Co Ltd Changsha 410029 Peoples R China

Compared with isolated stone columns, a group of stone columns exhibits a much more complicated failure mechanism because of the complicated interactions between the respective columns and the surrounding soil under various loadings, as well as the influence of the relevant geometries. Here, a numerical study based on the discrete-element method and finite-difference method coupled model was conducted to simulate the complete load-bearing process of stone column groups and to better understand the deformation and failure mechanisms of stone column groups in soft soil in response to rigid loading. The load settlement curves for the columns, soil, and loading plate were determined as the displacement and stress evolution. Moreover, the shear strain distribution indicating the ground failure mode during the complete loading process was visualized. Parametric studies considered the influences of the column arrangement, the soil strength, and various stiffnesses. The bearing capacity of individual columns within a stone column group varies due to the differing stress states of the surrounding soil. Edge columns typically fail first, thus transferring load to the internal columns. With a smaller number of columns, transferred loads can trigger internal column failures, resulting in overall instability of the column group. The strength and stiffness of the surrounding soil govern the stone column-bearing capacity. However, existing bearing capacity formulas primarily rely on soil strength parameters, ignoring the significance of soil stiffness.

关键词： Stone column Group column Numerical simulation Failure Interaction discrete-element method Universal distinct element code

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Deep Excavation-Induced Stability Evaluation of a Triple Tunnel Using discrete and Continuum Numerical Modeling

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2025年第1期25卷

作者： Tabaroei, Abdollah Sarfarazi, Vahab Moaveni, Maziar Vakili, Amir Hossein Pham, Tuan A. Eshragh Inst Higher Educ Dept Civil Engn Bojnourd *** Iran Hamedan Univ Technol Dept Min Engn Hamadan 65155579 Iran Savannah State Univ Dept Engn Technol Savannah GA 31404 USA Zand Inst Higher Educ Fac Engn Dept Civil Environm Engn Shiraz *** Iran Heriot Watt Univ Sch Energy Geosci Infrastructure Edinburgh EH14 4AS Scotland KTH Royal Inst Technol Dept Civil & Architectural Engn Stockholm Sweden

One of the most crucial tasks in the design, control, and construction of urban deep excavations is ensuring the safety of the existing underground infrastructure. Deformation and settlement created by excavation may damage the adjacent tunnels. In this study, the stability of an existing triple tunnel in relation to the construction of an adjacent deep excavation is evaluated by numerical simulation using both the discrete-element method (DEM) and the finite-element method (FEM). A deep excavation supported by the retaining wall and five levels of strutting system was created adjacent to an existing triple tunnel. The excavation's width and depth were 30 and 16 m, respectively. In both discrete-element (DE) and finite-element (FE) simulations, the horizontal spacing of the triple tunnel wall relative to the retaining wall (SH) is varied between 3 and 35 m, while vertical spacing of the triple tunnel's crown from the ground surface (SV) is changed from 4.8 to 32 m. The results indicated that at a certain value of SV and with increasing the SH, the horizontal displacement of the wall decreases. The variations in the triple tunnel position significantly affected the settlement pattern. In addition, the results showed that the maximum vertical displacement occurred at the middle tunnel crown, while the lowest value of the maximum vertical displacement was found at the crown of the right tunnel. At a certain value of the vertical displacement, the wall horizontal displacement is deduced by increasing in the SH value.

关键词： Excavation Triple tunnel Retaining wall Numerical simulation discrete-element method FEM

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