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Permeability and suction characteristics of compacted unbound aggregatesAbbott, Helen Amanda January 1990 (has links)
No description available.
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The stiffness and yielding anisotrophy of sandKuwano, Reiko January 1999 (has links)
No description available.
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Granular Attrition due to Rotary Valve in a Pneumatic Conveying SystemYao, Jun, Wang, Chi-Hwa, Lim, Wee Chuan 01 1900 (has links)
The rotary valve is a widely used mechanical device in many solids-handling industrial processes. However, it may also be responsible for most of the attrition effects occurring in a typical process. In this study, the attrition effects occurring in a rotary valve operating as a stand-alone device and as part of a pneumatic conveying system were investigated. In the former case granular attrition was carried out at three different rotary valve speeds and the experimental results obtained were found to be in good agreement with the Gwyn correlation. In the latter case three typical air flow rates were used in the pneumatic conveying system. The size distribution of the attrition product obtained at the lowest air flow rate used was not adequately described by the Gwyn correlation. The attrition process and mechanisms involved were analysed and the minimum size of the attrition product obtained from both modes of operations was found to be similar. / Singapore-MIT Alliance (SMA)
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Influence of specimen geometry and grading curve on the performance of an unbound granular materialVan Zyl, Eben Barnard 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This research study investigates the influence of specimen geometry and grading
curve, on the performance of a typical South African unbound granular material. The
experimental design incorporates three grading curves to evaluate the influence of
grading. In addition, to evaluate the influence of specimen geometry, two specimen
sizes were included into the experimental design. Laboratory testing consisted of
monotonic tri-axial tests to evaluate the shear performance (Cohesion and Friction
Angle) and more complex short duration dynamic tri-axial tests to evaluate the load
spreading ability/stiffness (Resilient Modulus) of the selected materials.
In order to achieve the objectives of this study, a large tri-axial apparatus was
needed that could accommodate specimens as large as 300mm ϕ * 600mm high.
This would allow a full grading of large aggregate (up to 50mm particle size) to be
accurately evaluated. Further development and commissioning of such a large triaxial
apparatus therefore formed part of this study.
The representative parent material selected for testing consisted of a G2 graded
crushed Hornfels stone. The material was dried and sieved into fractions where after
it was carefully reconstituted to allow for accurate control of specimen grading during
specimen preparation. The three grading curves consisted of two adjusted grading
curves (referred to as S19 and G19C), adjusted from the full G2 grading, and the full
G2 grading itself (referred to as the Full grading curve).
Material property tests, Sieve Analysis, Bulk Relative Density (BRD) and Optimum
Moisture Content (OMC) tests were performed to gain an understanding of the
material characteristics. Moisture-Density relationship curves were developed to
identify a common Moisture Content that, for all three grading curves, would yield a
common Dry Density. A Moisture Content of 4.7% was identified that would yield a
Dry Density of 2340 kg/m3 for all three grading curves. This density could be
achieved for both sizes of specimen preparation apparatuses without damaging
material particles. Specimens were compacted using the representative vibratory
hammer compaction method, sealed and left for 24 hours to allow redistribution of moisture and initial development of Cohesion.
The shear parameters (Cohesion and Friction Angle) were investigated through monotonic tri-axial testing. It was found that Cohesion and Friction Angle are
influenced by both grading curve and specimen geometry. Cohesion was found to
reduce as the coarseness of the material grading increased (i.e. finer S19 grading
yielded higher Cohesion than its coarser G19C counterpart) and the Friction Angle
was found to increase with increase coarseness (i.e. finer S19 grading yielded lower
Friction Angles when compared to the G19C grading).
The influence of specimen geometry was also investigated. It was observed than
Cohesion decreased with an increase in specimen size. Friction Angle on the other
hand was found to increase with increased specimen size.
From dynamic tri-axial test results, it was observed that the Resilient Modulus is
influenced by both specimen geometry and grading curve. The influence of specimen
geometry however is complex and no constant trend throughout the grading curves
tested could be identified. Grading curve however was found to increase the Resilient
Modulus for coarser gradings (i.e. coarser G19C vs finer S19). Increased large
particle-to-particle contact area yields higher friction within the material specimen,
resulting in lower strains induced by higher stresses, i.e. higher Resilient Modulus.
It was shown, for both monotonic and dynamic tri-axial tests, that the coarser G19C
grading curve yields more representative results to that of the Full grading curve
when compared to the finer S19 grading. This was observed for shear and resilient
performance properties. Additionally, a simple design case study yields similar
trends.
In conclusion, material characterisation plays an important role in the design of
unbound granular materials (UGM’s). Current laboratory characterisation techniques
however used adjusted gradings to limit the effects stemming from the ratio between
specimen diameter and maximum particle size. This research has shown that some
of the current practices do not best represent the true in-situ grading. It has been
shown that both grading curve and specimen geometry influence the performance of
UGM’s which, in turn, influences the design of a pavement structure. Therefore, accurate modelling of the true in-situ grading, through testing apparatuses capable of
accommodating in-situ gradings, is required. / AFRIKAANSE OPSOMMING: Hierdie navorsingsstudie evalueer die invloed van proefstukgeometrie en gradering,
op die gedragseienskappe van ‘n tipiese Suid Afrikaanse ongebinde granulêre
aggregaat. Om die invloed van gradering te evalueer, is ‘n eksperimentele ontwerp
ontwikkel wat drie materiaal graderings insluit. Verder, om die invloed van
proefstukgeometrie te evalueer, is twee proefstukgroottes toegevoeg tot die
eksperimentele ontwerp. Monotoniese drie-assige toetse is uitgevoer om die
skuifsterkte (Kohesie en Wrywingshoek) van die materiaal te ondersoek. Addisioneel
is die styfheid (Veerkragmodulus) van die materiaal ondersoek deur dinamiese drieassige
toetse.
Om die doelwitte van hierdie studie te bereik was ‘n groot skaalse die-assige toets
apparaat benodig wat groot, 300mm ϕ * 600mm hoogte, proefstukke kan
akkommodeer. So ‘n apparaat laat toe dat die volle gradering van aggregaat (tot en
met 50mm korrels) akkuraat geëvalueer kan word. Daarom vorm die ontwikkeling en
opstelling van so ‘n apparaat deel van hierdie studie.
Die tipiese Hornfels gebreekte klip, met ‘n G2 gradering, wat ondersoek is, was
gedroog en in verskeie fraksies gesif om die akkuraatheid van proefstuk
voorbereiding te beheer. Die drie graderings bestaan uit twee aangepaste graderings
(S19 en G19C gradering skale), aangepas vanaf die volle G2 gradering, en die vol
G2 gradering homself (verwys na as die “Full” gradering skaal).
Materiaal gedragstoetse, Sif Analises, Nat Gekompakteerde Relatiewe Digtheid
(BRD) en Optimum Vog Inhoud (OVI) toetse, was uitgevoer om die materiaal
eienskappe te ondersoek. Om ‘n gemeenskaplike Vog Inhoud en Droë Digtheid, wat
vir al drie graderings geld, te vind, is Vog-Digtheid verhoudingskurwes ontwikkel.
Vanaf die kurwes is identifiseer dat ‘n Vog Inhoud van 4.7% ‘n Droë Digtheid van
2340 kg/m3 vir al drie graderings sal lewer. Vibrasie kompaksie is toegepas om albei
skale van proefstukke te kompakteer waarna die proefstukke vir 24 uur geseel is om
vogverspreiding en ontwikkeling van Kohesie toe te laat.
Monotoniese drie-assige toetse is uitgevoer om die skuifsterkte parameters (Kohesie en Wrywingshoek) te ondersoek. Die resultate het gewys dat beide gradering en
proefstukgeometrie die Kohesie en Wrywinshoek beinvloed. gradering lewer hoër Kohesie waardes i.v.m. die growwer G19C gradering). Die
Wrywingshoek is gevind om te verhoog soos die grofheid van die gradering verhoog
(m.a.w. die fyner S19 gradering het laer Wrywingshoeke gelewer i.v.m. die growwer
G19C gradering).
Resultate het verder gewys dat groter proefstukke laer Kohesie en hoër
Wrywingshoeke lewer. Daar kan wel gedebateer word dat variasie in materiaal die
verandering van die skuifsterkte parameters gee, maar die proefstukvariasie is
beperk om sodoende die invloed daarvan onopmerkbaar te maak.. Verder is die
verlaging in Kohesie en verhoging in Wrywingshoek, a.g.v. ‘n vergroting in proefstuk
grootte, vir albei aangepaste graderings geobserveer. Dit is ‘n moontlike aanduiding
dat die verandering nie materiaal afhanklik is nie maar eerder beinvloed word deur
die grens toestande tydens kompaksie.
Dinamiese drie-assige toets resultate het gewys dat die Veerkragmodulus beinvloed
word deur beide proefstuk geometrie en gradering. Daar is gevind dat die invloed van
proefstukgeometrie kompleks is, en geen konstante verhouding, wat vir alle toets
graderings geld, kon identifiseer word nie. Vir die invloed van gradering is daar
gewys dat die Veerkragmodulus hoër is vir die growwer gradering (m.a.w. G19C
gradering lewer hoër styfheid as S19 gradering). ‘n Verhoging in korrel-tot-korrel
kontak area lewer hoër interne wrywing in die proefstuk wat bydrae tot laer
vervorming by hoër spannings, m.a.w. hoër Veerkragmodulus.
Baie interessant, vir beide monotoniese en dinamiese drie-assige toetse is gevind
dat die growwer G19C gradering, i.v.m. die fyner S19 gradering, die ware G2 (Full)
gradering beter verteenwoordig. Hierdie observasie is geldig vir beide die skuifsterkte
parameters en weerstands eienskappe.
Aggregaat karakterisering is ‘n belangrike deel in die ontwerp van ‘n ongebinde granulêre materiaal laag. Huidige karakterisering metodes gebruik aangepaste
graderings sodat resultate nie beinvloed word deur die verhouding tussen proefstuk
diameter en maksimum klipgrootte nie. Hierdie ondersoek het gevind dat van die
huidige aanpassings nie die ware gradering verteenwoordig nie. Die resultate wys
dat beide gradering en proefstuk geometrie die gedrag van die ongebinde granulêre
materiaal beinvloed, so ook die ontwerp van ‘n padstruktuur. Daar is dus ‘n behoefte
om die ware gradering te ondersoek wat slegs moontlik is met groot skaalse toets
apparaat, wat groot klip korrels kan toets. Verder, indien daar ‘n verstandhouding tussen huidige (klein skaalse) toets apparaat en groot skaalse apparaat ontwikkel
kan word, kan resultate aangepas word, vanaf die klein skaalse resultate, om die
ware materiaal gedrag meer te verteenwoordig.
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Dynamic analysis of non-steady flow in granular dense phase pneumatic conveyingTan, Shengming January 2009 (has links)
Research Doctorate - Doctor of Philosophy (PhD) / Slug flow dense phase pneumatic conveying can be a most reliable, efficient method for handling a remarkably wide range of dry bulk solids. Models for pressure drop over slugs in the low-velocity slug-flow pneumatic conveying by many researchers only took the force balance into account with the pressure drop. However, the nature of the slug flow pneumatic conveying is discontinuous and seldom becomes steady during the conveying period which requires further investigation. The fundamental understanding to gas/slug interaction in this thesis is that, by being a dynamic system, the faster a slug moves at a speed, the larger the space is left behind the slug. The gas feeding into the conveying system has to fill the increased space first then permeates through the slug and provides a push force on the slug. With gas permeation rate defined by the permeability factor, the derivative of the upstream pressure based on the air mass conservation law has been developed. For a given conveying system, the pressure in the pneumatic conveying system can be solved for steady conditions or numerically simulated for unsteady conditions. Parametric analysis have been conducted for pressure drop factors and found that slug velocity is the major reason causing the pressure fluctuation in the pneumatic conveying system. To verify the pressure drop model, this model has been applied to single slug cases and compared with experimental results for five different bulk materials, showing good results. Three distinct zones, i.e. Fixed Bed Zone, Initial Slug Zone and Reliable Slug Zone, have been found to exist in the relationship between slip velocity and pressure gradient. Lastly this model has also been applied to a multiple slug system under uniform conditions. In all, the fundamental gas pressure/pressure drop model developed in this thesis approaches slug flow conveying from a different viewpoint from the traditional momentum and material stress models developed by previous researchers, and provides a way of assessing the non-steady flow behaviour in granular dense phase pneumatic conveying. This model not only attains a better understanding of slug flow behaviour but also increases the accuracy of predicting the parameters.
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Dynamic analysis of non-steady flow in granular dense phase pneumatic conveyingTan, Shengming January 2009 (has links)
Research Doctorate - Doctor of Philosophy (PhD) / Slug flow dense phase pneumatic conveying can be a most reliable, efficient method for handling a remarkably wide range of dry bulk solids. Models for pressure drop over slugs in the low-velocity slug-flow pneumatic conveying by many researchers only took the force balance into account with the pressure drop. However, the nature of the slug flow pneumatic conveying is discontinuous and seldom becomes steady during the conveying period which requires further investigation. The fundamental understanding to gas/slug interaction in this thesis is that, by being a dynamic system, the faster a slug moves at a speed, the larger the space is left behind the slug. The gas feeding into the conveying system has to fill the increased space first then permeates through the slug and provides a push force on the slug. With gas permeation rate defined by the permeability factor, the derivative of the upstream pressure based on the air mass conservation law has been developed. For a given conveying system, the pressure in the pneumatic conveying system can be solved for steady conditions or numerically simulated for unsteady conditions. Parametric analysis have been conducted for pressure drop factors and found that slug velocity is the major reason causing the pressure fluctuation in the pneumatic conveying system. To verify the pressure drop model, this model has been applied to single slug cases and compared with experimental results for five different bulk materials, showing good results. Three distinct zones, i.e. Fixed Bed Zone, Initial Slug Zone and Reliable Slug Zone, have been found to exist in the relationship between slip velocity and pressure gradient. Lastly this model has also been applied to a multiple slug system under uniform conditions. In all, the fundamental gas pressure/pressure drop model developed in this thesis approaches slug flow conveying from a different viewpoint from the traditional momentum and material stress models developed by previous researchers, and provides a way of assessing the non-steady flow behaviour in granular dense phase pneumatic conveying. This model not only attains a better understanding of slug flow behaviour but also increases the accuracy of predicting the parameters.
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Effect of density and moisture content on the resilient response of unbound granular materialVan Aswegen, Elsabe January 2013 (has links)
Unbound granular material is used in the pavement structure and usually comprises the bulk of the
structural and foundation layers of a typical South African pavement. The term ‘unbound granular
material’ refers to the classification of natural material, which has not been modified in any way.
Various mechanistic-empirical models for the resilient response of unbound granular material have
been developed over the years. However, few have incorporated important influencing parameters such
as moisture or density on the basic stress-strain relationship or linked variables of the models to basic
engineering properties of unbound granular material.
This study builds on previous work by Theyse (2008a) and the cord modulus model developed by
Theyse (2012). The Theyse (2012) model was selected to be further investigated, since it modelled the
trends observed in the data realistically. The model depicts the stress dependent behaviour of unbound
granular material, where an increase initial modulus is observed for increasing confinement pressure,
as well as initial stress-softening with increasing stress ratio followed by stress stiffening.
The model was calibrated for all bulk material samples under consideration in this thesis. The calibration
process included linking variables of the model to mathematical functions that approximate the trends
observed when variables were considered against level of saturation. A parametric analysis indicated
that the saturation and stress-dependent cord modulus model realistically predict material behaviour.
The saturation and stress-dependent cord modulus model was refined further and calibrated for crushed
and natural unbound granular material. This refinement did not negatively influence the accuracy or
ability to realistically predict the material behaviour.
Basic material properties could be linked to predictive statistical distributions that could estimate the
range of modulus values that can be expected for the material under consideration. However, the
variables of the saturation and stress-dependent cord modulus model could not be linked to basic
material properties due to the limit set of results
available. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Civil Engineering / unrestricted
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Hot spots in ammonium nitrateTaylor, Nicholas January 2011 (has links)
Ammonium nitrate (AN) is commonly used as an explosive and as a fertilizer. In both roles it is provided as prills or pellets, approximately spherical and a few millimetres in diameter. The microstructures of several commercially-available AN compositions were investigated usingenvironmental scanning electron microscopy (ESEM) and X-ray microtomography. Those intended for explosive use were found to bemore porous than those intended for fertilizer use. The pores in explosiveprills were also found to form a connected network. The elemental composition of pellets of mixed AN and dolomite was investigated using energy-dispersive X-ray spectroscopy (EDX); the dolomite additivewas found to take the form of grains roughly 50 μm in size. The compaction behaviour of confined cylindrical beds of these prillsand pellets was studied at strain rates between 4 x 10-4 s-1 and 200 s-1. Quasi-static experiments were performed using a screw-driven instrumented press, while higher-rate experiments used a drop weight,instrumented with a line laser and load cell. The resistance of a bed to compaction was found to depend on the microstructure of its prills in most cases. Denser prills offered greater resistance to compaction. The exception to this rule was a pellet, rather than prill, formulation. Beds were also found to offer more resistance to compaction at higher strain rates. The Kawakita compaction model was found to agree well with the experimental data. A commercial fertilizer, not containing any AN, was assessed for use as an inert mock for AN prills and pellets. Prills of a suitable size for this purpose were found using EDX to consist of P2O5, with a coatingof unknown composition. They were supplied mixed with smaller K2CO3 and urea prills. The mixture was found to have comparablecompaction behaviour to AN compositions, indicating that it was useful as a mock for those compositions. In a plate impact experiment on a single layer of P2O5 prills, very little light was observed. Thisindicated that these prills were sufficiently inert for these purposes. The light produced by shocked granular ammonium nitrate beds and single prill layers was investigated using high-speed framing photography, photodiodes and gated visible-light spectroscopy. Framing photography of prill layers suggested that reaction in prill beds was dominatedby effects internal to prills. This was further supported by the similarity between photodiode recordings of prill beds and beds of inert prills containing a single reactive prills. Framing photography of drop weight experiments searching for a mechanism for initiation of reaction by interaction between prills found nothing. Decay of the light output of the beds suggested that in both granularand prill beds this light output was due to small regions heated to thousands of kelvin, which then cooled. Spectroscopic study confirmed this. These regions were found to reach a peak temperature of 6660 ± 20 K, well in excess of the approximately 2000 K predicted by a simple chemical model. Investigation of spectral lines observedduring this study indicated that the exothermic reaction that led to heating of these emitting regions involved NO.
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Simulation based exploration of a loading strategy for a LHD-vehicle / Simuleringsbaserad utforskning av styrstrategier för frontlastareLindmark, Daniel January 2016 (has links)
Optimizing the loading process of a front loader vehicle is a challenging task. The design space is large and depends on the design of the vehicle, the strategy of the loading process, the nature of the material to load etcetera. Finding an optimal loading strategy, with respect to production and damage on equipment would greatly improve the production and environmental impacts in mining and construction. In this thesis, a method for exploring the design space of a loading strategy is presented. The loading strategy depends on four design variables that controls the shape of the trajectory relative to the shape of the pile. The responses investigated is the production, vehicle damage and work interruptions due to rock spill. Using multi-body dynamic simulations many different strategies can be tested with little cost. The result of these simulations are then used to build surrogate models of the original unknown function. The surrogate models are used to visualize and explore the design space and construct Pareto fronts for the competing responses. The surrogate models were able to predict the production function from the simulations well. The damage and rock spill surrogate models was moderately good in predicting the simulations but still good enough to explore how the design variables affect the response. The produced Pareto fronts makes it easy for the decision maker to compare sets of design variables and choose an optimal design for the loading strategy.
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Micromechanical Analysis of Induced Anisotropy in Granular MaterialsShi, Jingshan January 2018 (has links)
Granular materials, such as sand, are systems consisting of huge numbers of particles that interact with each other through inter-particle contacts. Different from continuum materials, a granular material displays distinctive features due to the discrete nature of the microstructure, characterized by a spatial arrangement of inter-particle connection as well as a force-chain network. With a consideration of the contact force, the overall contact network is divided into a strong sub-network and a weak sub-network that carry contacts with normal contact forces larger and lower than the average normal contact force, respectively. Thus, the fabric anisotropy for different contact networks, are employed to characterize the microstructure of the granular material.
In this research, the behavior of granular materials subjected to quasi-static shear was extensively investigated in terms of the fabric evolution including the magnitude and direction of anisotropy for different contact networks. Both statistical and micromechanical approaches were adopted to obtain the macroscopic properties, such as the fabric tensor, Cauchy stress tensor and the second-order work, in terms of the micro-scale variables. The discrete element method (DEM) was employed to simulate laboratory tests along fixed loading paths; for example, 2D tests along proportional strain paths, 2D simple shear tests and 3D tests along radial stress paths on the π-plane.
Results demonstrated that the induced fabric anisotropy for the overall contact network can be related to the deviatoric stress ratio for both two-dimensional and three-dimensional conditions. The relation was found to be not unique, depending on the loading paths as well as the stress state. Nevertheless, a unique linear fabric-stress relation was presented between the stress tensor and fabric tensor for the strong sub-network. Specifically, the obliquity of this linear relation was found to be a function of the mean stress. This description held true for initially isotropic specimens subjected to proportional and non-proportional loading paths. On the other hand, for the initially anisotropic specimen, this correspondence only worked at the critical stress state.
According to Nicot and Darve (2006), the macro second-order work cannot be interpreted as a summation of the local second-order work from the contact plane. The second-order work induced by the fabric evolution and the volumetric change must also be taken into account. The second-order work induced by the fabric evolution cannot be neglected in 2D analysis along proportional strain paths. Moreover, the vanishing of the second-order work is related to the fabric anisotropy in contact sub-networks that the decrease of fabric anisotropy for the weak sub-network or the degradation of weak sub-network was observed to be an indicator of deformation instability even though the strong sub-network dominants the shear resistance. The degradation of strong sub-network was a necessary but not a sufficient condition of instability.
The direction of the fabric anisotropy for the strong sub-network was observed to be coaxial with the orientation of the principal stress. The principal direction of fabric anisotropy for the weak sub-network was always perpendicular to that of the strong sub-network, regardless of whether the principal stress rotated or not. For the overall contact network, however, the direction of the fabric anisotropy was not necessarily in line with the major principal stress direction, even for an initial isotropic granular assembly. Therefore, the finding by Radjaï et al.(1998) that the direction of the fabric anisotropy for the weak sub-network is perpendicular to that for the overall contact network only held true for the loadings in which the critical stress could be approached no matter if the principal stress orientation rotated or not. Under this circumstance, the fabric anisotropy for the overall contact network could be interpreted as a function of sub-networks’ anisotropy weighted by the ratio of contact number in each sub-network over the total number of contacts.
At critical state, both the strong sub-network and the overall contact network developed high fabric anisotropy with the weak sub-network being mostly isotropic. When plotted on the π-plane, both the fabric anisotropy for the strong sub-network and the fabric anisotropy for the overall contact network depended on the stress paths but were independent of the mean stress level. The response surface of the former could be expressed as a Lade’s surface. The response envelope of the latter was an inverted Lade’s surface. / Dissertation / Doctor of Philosophy (PhD) / In civil engineering, granular materials are ubiquitous, such as sand, gravel, rock, and concrete. Due to the discrete nature of microstructure, this type of material usually displays exceedingly complicated behaviours under shear, for example, dilatancy, non-coaxiality, critical state, instability, and anisotropy. These mechanical responses are notoriously difficult to model and most existing models are phenomenological and lack a clear physical meaning. To provide a clear physical meaning for the constitutive model of granular material, the current study explored the evolution of the microstructure within the granular material subjected to quasi-static shear and the micromechanical origins of those macroscopic behaviours such as critical state, non-coaxiality, and instability. Both micromechanical analysis and discrete element method were applied. Results showed that the evolution of the whole microstructure depended on the loading condition. However, the evolution of the microstructure joined by the ‘strong contacts’ was independent of the loading path. At critical state, the microstructure was highly anisotropic, not unique and depended on the stress paths. The rearrangement of the microstructure helped to maintain the stability of a granular material. The instability of the granular material was triggered by the failure of the microstructure joined by the ‘weak contacts’.
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