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DEM simulations of critical state behaviour of granular materials under various drained triaxial stress path tests

Particuology 2023年第10期81卷 98-108页

作者： shiva prashanth kumar kodicherla Guobin Gong Stephen Wilkinson Department of Civil Mining and Process EngineeringNamibia University of Science and TechnologyWindhoekNamibia Department of Civil Engineering Xi’an Jiaotong-Liverpool UniversitySuzhouChina Faculty of Engineering and Information Sciences University of WollongongDubai CampusDubaiUnited Arab Emirates

The present study investigates the critical state behaviour of granular assemblies composed of clumped particles under four different drained axisymmetric triaxial stress paths,using the discrete element method(DEM).A series of numerical samples were prepared at initial states with different density indexes(1D)and different initial confining pressures(ρ′0).These samples were sheared to large strains,at which constant stresses and volumes were maintained to reach the critical *** evolution of stress ratio under the same loading mode(for the same intermediate principal stress ratio,b)is shown to yield an almost identical behaviour independent of stress paths,whereas the stress-strain response depends on the stress *** different axisymmetric stress paths all share the same unique friction angle at critical state,indicating the Mohr-Coulomb failure criterion is the appropriate critical state strength criterion,which is at least true for the axisymmetric stress conditions.A unique coordination number(CN)is achieved at the critical state for a given po,which is independent of the stress *** critical state CN is found to increase with the increase in po,which could be attributed to the decrease in the critical state void ratio(ec)as mean effective stress(ρ′0)***,a unique linear functional relationship is found between the critical state values of cN and ec,and a unique polynomial functional relationship is found between the critical state values of CN andρ′.These functional relationships indicate no dependency on the stress paths or loading modes,thus characterizing unique features at critical states at both macroscopic and microscopic levels for a given type of granular material.

关键词： Discrete element method Critical state Drained behaviour Triaxial stress paths

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Discrete element modelling of strength and critical state characteristics of granular materials under axial compression and axial extension stress path tests

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Particuology 2021年第3期19卷 152-162页

作者： shiva prashanth kumar kodicherla Guobin Gong Lei Fan Stephen Wilkinson Charles K.S.Moy Department of Civil Engineering Xi’an Jiaotong-Liverpool University(XJTLU)China Department of Civil Engineering University of WollongongDubai

The critical state soil mechanics(CSSM)framework has been widely used across a range of problems in geomechanics involving complex loading ***,the uniqueness of the critical state has been disputed for many years and it remains a controversial *** by previous investigations,a series of discrete element method(DEM)simulations were performed under both axial compression(AC)and axial extension(AE)stress *** samples were isotropically compressed at varying mean normal effective stresses(confining pressures)and sheared to a large axial strain of approximately 60%.It is found that there exist unique values of critical void ratios and stress ratios under critical state,which are independent of the samples’initial packings but dependent on stress *** the critical strength(stress ratio)for the AC stress path tests is higher than that for the AE stress *** critical state lines(CSLs)are found to path-dependent but unique for each stress path.A unique linear relationship between the critical coordination numbers and critical void ratios is identified under the AC and AE stress paths respectively,but such a relationship depends on the stress *** is also found that there exist unique values of microscopic parameters in terms of deviator fabric under critical state,which are independent of the samples’initial packings but dependent on stress *** these simulation results lead to the conclusion of non-uniqueness of CSLs from both macroscopic and microscopic viewpoints.

关键词： DEMClumped particles Critical state Densification index State parameter

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Investigations of the effects of particle morphology on granular material behaviors using a multi-sphere approach

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第6期12卷 1301-1312页

作者： shiva prashanth kumar kodicherla Guobin Gong Lei Fan Stephen Wilkinson Charles K.S.Moy Department of Civil Engineering Xi’an JiaotongeLiverpool University(XJTLU)Suzhou215123China Department of Civil Engineering and Industrial Design University of LiverpoolLiverpoolUK Department of Civil Engineering University of WollongongDubaiUAE

This article studies the influences of particle morphology on the behaviors of granular materials at both macroscopic and microscopic levels based on the discrete element method(DEM).A set of numerical tests under drained triaxial compression was performed by controlling two morphological descriptors,*** of the smallest to the largest pebble diameter,x,and the maximum pebbleepebble intersection angle,*** descriptors are vital in generating particle geometry and surface *** was found that the stress responses of all assemblies exhibited similar behavior and showed post-peak *** normalized stress ratio and volumetric strains flatten off and tended to reach a steady value after an axial strain of 40%.While the friction angles at peak state varied with different morphological descriptors,the friction angles at critical state showed no significant ***,evolution of the average coordination numbers showed a dramatic exponential decay until an axial strain of about 15%after which it stabilized and was unaffected by further increase of axial *** addition,stress ratio q/p and strong fabric parameter fs d=fs m were found to follow an approximately linear relationship for each *** findings emphasized the significance of the influences of particle morphology on the macroscopic and microscopic responses of granular materials.

关键词： Discrete element method(DEM) Particle morphology Granular materials Triaxial compression Fabric

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