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Influence of fabric anisotropy on seismic responses of foundations

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第2期7卷 147-154页

作者： Jin Qin Xiangwu Zeng Haiyan Ming Department of Civil Engineering Case Western Reserve University Department of Civil Engineering Shenzhen University

Earthquakes, as one of the well-known natural disasters, are highly destructive and *** failure due to liquefaction induced by earthquakes can cause casualties as well as significantdamage to the building itself. fabric anisotropy of soil grains is considered to be an important factor indynamic soil response based on previous researches and laboratory tests. However, the limited availabilityof real physical data makes it less persuasive. In this study, a shake table installed on ageotechnical centrifuge is used to provide the designed seismic motions, and therefore, to simulate therealistic earthquake motion to foundations. Important parameters in the responses such as acceleration,excess pore pressure and deformation are evaluated to investigate the influence. Implications for designare also discussed. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

关键词： Soil mechanics Angular sand Centrifuge modeling fabric anisotropy Seismic response

Study on meso-mechanical behavior of sand based on its 2D geometrical model

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Science China(Technological Sciences) 2020年第5期63卷 777-790页

作者： XU WenJie FENG ZeKang YANG Han LIU GuangYu State Key Laboratory of Hydroscience and Hydraulic Engineering Department of Hydraulic EngineeringTsinghua UniversityBeijing 100084China Department of Civil and Environmental Engineering University of CaliforniaDavisCA 95616USA

A comprehensive study on the meso-mechanical behaviors of sand with its 2D geometrical models was presented in this *** on the 2D geometrical models,database of sand particles,quantitative analysis on the geometrical characteristics of the studied sand particles was performed.A new clump generation algorithm based on fewer multiple overlapping circles was provided to accurately model the shape of sand particles,and was used to build the discrete element method(DEM)numerical model of the sand sample for DEM biaxial *** macro-and meso-mechanical behaviors of the studied sand samples were systematically *** was mainly localized in a X-shaped shear zone,in which the particles experienced large displacements and *** of stress-induced anisotropy in particle and void orientations,as well as the mesoscopic fabric,was significant during the shearing *** collapse,generation,reduction,and extension of force chains occurred during the shearing process,especially after the peak stress was *** led to the fluctuations in the evolution of deviatoric stress and volumetric strain at macroscale,as well as the fabric anisotropy at mesoscale.

关键词： sand particle shape deformation localization fabric anisotropy discrete element method(DEM)

A DEM investigation on simple shear behavior of dense granular assemblies

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Journal of Central South University 2015年第12期22卷 4844-4855页

作者：史旦达薛剑峰赵振营史跻宇 School of Ocean Science and Engineering Shanghai Maritime University School of Engineering and Information Technology Federation University Australia Jiangsu Zhongshe Engineering Consultancy Group

A micromechanical investigation on simple shear behavior of dense granular assemblies was carried out by discrete element *** series of numerical tests were performed to examine the effects of initial porosity,vertical stress and particle shape on simple shear behavior of the samples,*** was found that during simple shear the directions of principal stress and principal strain increment rotate differently with shear strain *** non-coaxiality between the two directions decreases with strain level and may greatly affect the shear behavior of the assemblies,especially their peak friction *** numerical modelling also reveals that the rotation of the principal direction of fabric anisotropy lags behind that of the major principal stress direction during simple shear,which is described as fabric hyteresis *** degrees of fabric and interparticle contact force anisotropies increase as particle angularity increases,whereas the orientations of these anisotropies have not been significantly influenced by particle *** extended stress–dilatancy relationship based on ROWE-DAVIS framework was proposed to consider the non-coaxiality effect under principal stress *** model was validated by present numerical results as well as some published physical test and numerical modelled data.

关键词： simple shear non-coaxiality fabric anisotropy shear strength discrete element method

Simulation of the deformable lateral boundaries in biaxial test using DEM

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Particuology 2024年第5期88卷 161-175页

作者： Ali Momeni Barry Clarke Yong Sheng Ali Hassanpour WSP 3 Wellington PlaceLeedsLS1 4APUK Hull University HullHU6 7RXUK School of Civil Engineering University of LeedsLeedsLS2 9JTUK School of Computer Science University of HullHullHU6 7RXUK School of Chemical and Process Engineering University of LeedsLeedsLS2 9JTUK

Applying the discrete element method(DEM)in soil mechanics can provide abundant information at the particle-scale and facilitates illustration of the macro-mechanical behaviour of soils based on the inter-particle *** triaxial test is one of the most common laboratory methods to study the macro-mechanical behaviour of particulate materials such as ***,many problems in geotechnical design can be assumed and simplified as a plane strain *** a biaxial test can be conducted to reproduce the macro-mechanical behaviour of soil,where the sample is enclosed by two horizontal rigid platens and a vertical latex membrane,which is a deformable continuous element and allows the enclosed specimen to deform freely while maintaining confining stress during *** paper presents an algorithm to represent physical and mechanical characteristics of latex membrane in the 2D DEM simulation of biaxial test using the PFC^(2D) *** investigate the impact of the lateral boundary conditions on the micro-macro mechanical behaviours of soil samples,two sets of DEM biaxial tests are conducted,*** rigid and deformable lateral boundary *** DEM modeling results indicate that the lateral boundary conditions have a significant effect on the micro-scale fabric properties,thickness and inclination of the shear *** comparison between these two simulations also demonstrates that the lateral boundary conditions play a major role in the peak and post-peak stress-strain behaviours as well as the dilation and critical state behaviours of granular soils.

关键词： Discrete element method Biaxial test Deformable boundaries Shear band Critical state fabric anisotropy Geometrical stability index

A numerical analysis of the shear behavior of granular soil with fines

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Particuology 2015年第4期13卷 160-172页

作者： Beibing Dai Jun Yang Xiaodong Luo Research Centre of Geotechnical Engineering and Information Technology Sun Yat-sen University Department of Civil Engineering The University of Hong Kong

Shear behavior of granular soil with fines is investigated using the discrete element method （DEM） and particle arrangements and inter-particle contacts during shear are examined. The DEM simulation reveals that fine particles play a vital role in the overall response of granular soil to shearing. The occurrence of liquefaction and temporary reduction of strength is ascribed mainly to the loss of support from the fine particle contacts （S-S） and fine particle-to-large particle contacts （S-L） as a consequence of the removal of fine particles from the load-carrying skeleton. The dilative strain-hardening response following the strain-softening response is associated with the migration of fine particles back into the load-carrying skeleton, which is thought to enhance the stiffness of the soil skeleton. During shear, the unit normal vector of the large particle-to-large particle （L-L） contact has the strongest fabric anisotropy, and the S-S contact unit normal vector possesses the weakest anisotropy, suggesting that the large particles play a dominant role in carrying the shear load. It is also found that, during shear, fine particles are prone to rolling at contacts while the large particles are prone to sliding, mainly at the S-L and L-L contacts.

关键词： Granular soil Fine particle Shear behavior Discrete element method fabric anisotropy Coordination number

Visualization of pullout behaviour of geogrid in sand with emphasis on size effect of protrusive junctions

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Journal of Central South University 2017年第9期24卷 2121-2133页

作者：苗晨曦郑俊杰章荣军谢明星殷建华 Institute of Geotechnical and Underground Engineering Huazhong University of Science and Technology Department of Civil and Environmental Engineering The Hong Kong Polytechnic University

Geogrid has been extensively used in geotechnical engineering practice due to its effectiveness and economy. Deep insight into the interaction between the backfill soil and the geogrid is of great importance for proper design and construction of geogrid reinforced earth structures. Based on the calibrated model of sand and geogrid, a series of numerical pullout tests are conducted using PFC^(3D) under special considerations of particle angularity and aperture geometry of the geogrid. In this work, interface characteristics regarding the displacement and contact force developed among particles and the deformation and force distribution along the geogrid are all visualized with PFC^(3D) simulations so that new understanding on how geogrid-soil interaction develops under pullout loads can be obtained. Meanwhile, a new variable named fabric anisotropy coefficient is introduced to evaluate the inherent relationship between macroscopic strength and microscopic fabric anisotropy. A correlation analysis is adopted to compare the accuracy between the newly-proposed coefficient and the most commonly used one. Furthermore, additional pullout tests on geogrid with four different joint protrusion heights have been conducted to investigate what extent and how vertical reinforcement elements may result in reinforcement effects from perspectives of bearing resistance contribution, energy dissipation, as well as volumetric response. Numerical results show that both the magnitude and the directional variation of normal contact forces govern the development of macroscopic strength and the reinforcing effects of joint protrusion height can be attributed to the accelerated energy dissipation across the particle assembly and the intensive mobilization of the geogrid.

关键词： geogrid pullout behaviour discrete element method (DEM) joint protrusion fabric anisotropy energy dissipation

Coupled effects of particle overall regularity and sliding friction on the shear behavior of uniformly graded dense sands

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 873-885页

作者： Jiayan Nie Shiwei Zhao Yifei Cui Yu Wang State Key Laboratory of Hydroscience and Engineering Tsinghua UniversityBeijing100084China South China Institute of Geotechnical Engineering South China University of TechnologyGuangzhou510640China Key Laboratory of Mountain Hazards and Surface Process Institute of Mountain Hazards and EnvironmentChinese Academy of SciencesChengdu610041China University of Chinese Academy of Sciences Beijing100049China

Particle morphology has been regarded as an important factor affecting shear behaviors of sands,and covers three important aspects,*** form(overall shape),local roundness(large-scale smoothness),and surface texture(roughness)in terms of different observation *** features of different aspects can be independent of each other but might have coupled effects on the bulk behavior of sands,which has been not explored thoroughly *** paper presents a systematic investigation of the coupled effects of the particle overall regularity(OR)and sliding friction on the shear behavior of dense sands using three-dimensional(3D)discrete element method(DEM).The representative volume elements consisting of ideal spheres and irregular clumps of different mass proportions are prepared to conduct drained triaxial compression simulations.A well-defined shape descriptor named OR is adopted to quantify particle shape differences of numerical samples at both form and roundness aspects,and the particle sliding friction coefficient varies from 0.001 to 1 to consider the surface roughness effect equivalently in *** stress-strain relationships as well as peak and critical friction angles of these assemblies are examined ***,contact network and anisotropic fabric characteristics within different granular assemblies are analyzed to explore the microscopic origins of the multi-scale shape-dependent shear *** study helps to improve the current understanding with respect to the influence of the particle shape on the shear behavior of sands from different shape aspects.

关键词： Discrete element method(DEM) Overall regularity(OR) Particle sliding friction Peak and critical friction angles fabric anisotropy Dense sands