An Analysis of the Strength of Anisotropic Granular Assemblies via Discrete Methods

2014 ◽  
Vol 553 ◽  
pp. 525-530
Author(s):  
Sergio Andres Galindo-Torres ◽  
Dorival Pedroso ◽  
David Williams ◽  
Hans Mühlhaus
Keyword(s):  
Shear Strength ◽  
Granular Media ◽  
Three Dimensional ◽  
Spherical Particles ◽  
Triaxial Tests ◽  
True Triaxial ◽  
Polyhedral Particles ◽  
Granular Assemblies ◽  
Mean Pressure ◽  
Confining Pressures

This paper presents a study on the macroscopic strength characteristics of granular assemblies with three-dimensional complex-shaped particles. Different assemblies are considered, with both isotropic and anisotropic particle geometries. The study is conducted using the Discrete Element Method (DEM), with so-called sphero-polyhedral particles, and simulations of mechanical true triaxial tests for a range of Lode angles and confining pressures. The observed mathematical failure envelopes are investigated in the Haigh-Westergaard stress space, as well as on the deviatoric-mean pressure plane. It is verified that the DEM with non-spherical particles produces results that are qualitatively similar to experimental data and previous numerical results obtained with spherical elements. The simulations reproduce quite well the shear strength of assemblies of granular media, such as higher strength during compression than during extension. In contrast, by introducing anisotropy at the particle level, the shear strength parameters are greatly affected, and an isotropic failure criterion is no longer valid. It is observed that the strength of the anisotropic assembly depends on the direction of loading, as observed for real soils.

Effect of Interparticle Friction on the Micromechanical Strength Characteristics of Three Dimensional Granular Media

2015 ◽  
Vol 16 ◽  
pp. 79-89
Author(s):  
Karinate Valentine Okiy
Keyword(s):  
Shear Strength ◽  
Principal Stress ◽  
Coordination Number ◽  
Granular Media ◽  
Three Dimensional ◽  
Contact Forces ◽  
Strength Characteristics ◽  
Fabric Anisotropy ◽  
Granular Assemblies ◽  
Interparticle Friction

The role of interparticle friction on the micromechanical strength characteristics of granular assembly subjected to gradual shearing was analyzed. Three dimensional discrete element method (DEM) was applied in the simulation of quasi-static shearing of granular assemblies with varying interparticle frictional coefficients [µ= 0.10, 0.25, 0.50]. From the reported simulation results, analysis of the following was performed for varying interparticle frictional capacities.i. The normal and tangential stress contributions of weak and strong contacts to principal stress components.ii. Contribution of strong and weak contacts to principal and deviator stress.iii. Evolution of mechanical coordination number and fabric anisotropy of strong contact forces.From this analysis, it is safe to conclude that interparticle friction has a direct effect on the major and minor principal stress components in sheared granular assemblies. Consequently, increasing interparticle friction capacity enhances macroscopic shear strength in sheared granular assemblies. Likewise, at the peak shear strength of the sheared granular media, there exists a maximum fabric anisotropy of strong contact forces and this corresponds to a minimum value of mechanical coordination number (minimum possible number of load bearing contacts per particle).

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

Anisotropic Behavior of Geomaterial under Three-Dimensional Stress States

2010 ◽  
Vol 160-162 ◽  
pp. 1425-1431
Author(s):  
Kun Yong Zhang ◽  
Yan Gang Zhang ◽  
Chi Wang
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Three Dimensional ◽  
Complex Stress State ◽  
Triaxial Tests ◽  
Induced Anisotropy ◽  
Principal Stresses ◽  
True Triaxial ◽  
Stress Effects ◽  
Stress Induced Anisotropy

Most soil constitutive models were developed based on the traditional triaxial tests with isotropic assumption, in which the load is applied as the major principal stress direction and the other two principal stresses are symmetric. When such isotropic models are applied to practical analysis, stress induced anisotropy under complex stress state and the middle principal stress effects are often neglected, thus there are many disagreements between the calculated results and the infield testing data. To simulate the practical loading process, true triaxial tests were carried out on geomaterial under three-dimensional stress state. It was found that the stress induced anisotropy effects are remarkable and the middle principal stress effects are obvious because of the initial three-dimensional stress state. Such kind of stress-induced anisotropy could have important impact on the numerical analysis results and should be taken into consideration when developing the constitutive model.

Strength and Interaction of Soil Reinforced with Three-Dimensional Elements

2007 ◽  
Vol 340-341 ◽  
pp. 1285-1290
Author(s):  
M.X. Zhang ◽  
S.L. Zhang ◽  
J.M. Peng ◽  
A.A. Javadi
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Shear Strength ◽  
Three Dimensional ◽  
Reinforced Soil ◽  
Experimental Results ◽  
Triaxial Tests ◽  
Retaining Structure ◽  
3D Elements ◽  
Element Method

For conventional reinforced soil, the reinforcements are put horizontally in the soil. A new concept of soil reinforced with three-dimensional elements was proposed. In 3D reinforced soil, besides conventional horizontal reinforcements, some vertical and 3D reinforcements can also be laid in the soil. The triaxial tests on sand reinforced with 3D reinforcement were carried out. From the experimental results, the differences of stress-strain relationship and shear strength between horizontal reinforced sand and 3D reinforced one were analyzed. The experimental results show that 3D reinforcement not only increases its cohesion, the angle of internal friction has been increased greatly, especially with 3D elements on both sides. Based on experimental results, a retaining structure reinforced with 3D reinforcements was analyzed by the finite element method. The stress distribution and interaction between 3D elements and soil were studied. The plastic zone and stability analysis of the retaining structure reinforced with 3D reinforcements were investigated by finite element method by shear strength reduction technique.

scholarly journals Effect of Geotextile Reinforcement on Shear Strength of Sandy Soil: Laboratory Study

2016 ◽  
Vol 38 (4) ◽  
pp. 3-13 ◽  
Author(s):  
Sidali Denine ◽  
Noureddine Della ◽  
Muhammed Rawaz Dlawar ◽  
Feia Sadok ◽  
Jean Canou ◽  
...  
Keyword(s):  
Shear Strength ◽  
Mechanical Behaviour ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Loose Sand ◽  
Test Results ◽  
Compression Tests ◽  
Confining Stress ◽  
Natural Sand ◽  
Confining Pressures

Abstract This paper presents results of a series of undrained monotonic compression tests on loose sand reinforced with geotextile mainly to study the effect of confining stress on the mechanical behaviour of geotextile reinforced sand. The triaxial tests were performed on reconstituted specimens of dry natural sand prepared at loose relative density (Dr = 30%) with and without geotextile layers and consolidated to three levels of confining pressures 50, 100 and 200 kPa, where different numbers and different arrangements of reinforcement layers were placed at different heights of the specimens (0, 1 and 2 layers). The behaviour of test specimens was presented and discussed. Test results showed that geotextile inclusion improves the mechanical behaviour of sand, a significant increase in the shear strength and cohesion value is obtained by adding up layers of reinforcement. Also, the results indicate that the strength ratio is more pronounced for samples which were subjected to low value of confining pressure. The obtained results reveal that high value of confining pressure can restrict the sand shear dilatancy and the more effect of reinforcement efficiently.

Assessment of the Mechanical Behaviour of Granular Media by DEM-Based True Triaxial Tests

2016 ◽  
Vol 846 ◽  
pp. 428-433
Author(s):  
J. Cabrejos-Hurtado ◽  
S. Galindo Torres ◽  
D.M. Pedroso
Keyword(s):  
Numerical Simulation ◽  
Mechanical Behaviour ◽  
Granular Media ◽  
Triaxial Tests ◽  
Granular Soils ◽  
True Triaxial Test ◽  
Virtual Sample ◽  
True Triaxial ◽  
Toyoura Sand ◽  
True Triaxial Tests

This study presents the numerical simulation of a true triaxial test by means of the discrete element method (DEM). Experimental results performed on Toyoura sand are employed as reference and the calibration methodology is explained. Physical aspects of the real soil, such as the grain size distribution and the relative density, are considered during the generation of the virtual sample. It is shown that the main aspects of the macro-mechanical behaviour of granular soils during compression loading can be fairly represented by the idealised simulations with particles.

scholarly journals LMGC90: a Contact Dynamics open source code for the simulation of granular asteroid with realistic regolith shapes. Application to the accretion process

2021 ◽  
Vol 249 ◽  
pp. 14007
Author(s):  
Paul Sánchez ◽  
Mathieu Renouf ◽  
Emilien Azéma ◽  
Rémy Mozul
Keyword(s):  
Open Source ◽  
Granular Media ◽  
Contact Stiffness ◽  
Three Dimensional ◽  
Contact Dynamics ◽  
Theoretical Concepts ◽  
Polyhedral Particles ◽  
Accretion Process ◽  
Particles Size Distribution ◽  
Self Gravity

Granular asteroids are naturally occurring gravitational aggregates (rubble piles) bound together by gravitational forces. For this reason, it is reasonable to use the theoretical concepts and numerical tools developed for granular media to study them. In this paper, we extend the field of applicability of the Contact Dynamic (CD) method, a class of non smooth discrete element approach, for the simulation of three dimensional granular asteroids. The CD method is particularly relevant to address the study of dense granular assemblies of a large number of particles of complex shape and broad particles size distribution, since it does not introduces numerical artefacts due to contact stiffness. We describe how the open source software LMGC90, interfaced with an external library for the calculation of self-gravity, is used to model the accretion process of spherical and irregular polyhedral particles.

Unified Three-Dimensional Revision of Modified Cam Clay Model

2007 ◽  
Vol 340-341 ◽  
pp. 1267-1272
Author(s):  
Hang Zhou Li ◽  
Hong Jian Liao ◽  
Kyoji Sassa ◽  
Gong Hui Wang
Keyword(s):  
Three Dimensional ◽  
Yield Function ◽  
Triaxial Tests ◽  
Strength Theory ◽  
Unified Strength Theory ◽  
True Triaxial ◽  
Proposed Model ◽  
Modified Cam Clay ◽  
Stress States ◽  
Cam Clay

According to unified strength parameters obtained from unified strength theory, the slope of critical state line is modified to reflect critical states of different geomaterials under general stress states. Yield function that can consider the effect of the third deviatoricic invariant is proposed, and an elasto-plastic constitutive model is established by adopting non-associated flow rules; furthermore, methods of overcoming singular points on the yield surface are discussed. The proposed model is verified by true triaxial tests of clay, and results show that the model can well predict stress-strain relationships.

Size Effects in a Slowly Sheared Granular Media

2001 ◽  
Vol 68 (5) ◽  
pp. 772-775 ◽  
Author(s):  
S. J. Antony ◽  
M. Ghadiri
Keyword(s):  
Stress Distribution ◽  
Granular Media ◽  
Stress Condition ◽  
Distinct Element ◽  
Three Dimensional ◽  
Size Ratio ◽  
Spherical Particles ◽  
Granular Systems ◽  
Periodic Cell ◽  
Large Particles

In this paper, we analyze the nature of stress distribution experienced by large particles in a dense granular media subjected to slow shearing, using the distinct element method. The particles were generated in a three-dimensional cuboidal periodic cell in which a large solid spherical particle was submerged (“submerged particle”) at the center of a bed of monodispersed spherical particles. The granular systems with different size ratio (i.e., the ratio of the diameter of submerged particle to that of the surrounding monodispersed particles) were subjected to quasi-static shearing under constant mean stress condition. The evolution of stress distribution in the submerged particle during shearing was carefully tracked down and presented here. The nature of stress distribution is bifurcated into two components, viz., (i) hydrostatic and (ii) deviatoric components. It has been shown that, for size ratio greater than c.a. 10, the nature of stress distribution in the submerged particle is hydrostatically dominant (increases the ‘fluidity’). For smaller size ratios, the nature of stress distribution in the submerged particle is dominantly deviatoric.

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