Publications
225 results found
Ciantia MO, O'Sullivan C, Arroyo M, et al., 2019, Breakage and critical state via DEM
Discrete-element simulations are used to explore the relation between breakage-induced grading evolution and the critical state line position on the compression plane. An efficient model of particle breakage is applied to perform a large number of tests, in which grading evolution is continuously tracked using a grading index. Using both previous and new experimental results, the discrete element model is calibrated and validated to represent Fontainebleau sand. The results obtained show that, when breakage is present, the inclusion of a grading index in the description of critical states is advantageous. This can be simply done using the critical state plane concept.
Ciantia MO, O’Sullivan C, Jardine RJ, 2019, Pile penetration in crushable soils: Insights from micromechanical modelling, Pages: 298-317
A 3D discrete element model (DEM) was used to simulate calibration chamber experiments of a cone shaped tip pile penetrating into crushable granular media. Both monotonic and cyclic jacking are considered. Particle crushing is simulated by employing a rigorous breakage criterion applied to elasto-brittle spheres. Particle scaling is used to limit the number of particles considered and it is shown that, above a threshold limit, the penetration curves become scale independent, provided a scalable crushing model is used. The particle crushing model parameters were calibrated by matching triaxial and one-dimensional compression tests. The DEM model could capture the stress measurements made around a model pile during and after its penetration into sand relatively well. The particle-scale mechanics that underlie the observed macroscopic responses are analysed, placing emphasis on the distribution of crushing events around the pile tip and distributions of particle stresses and forces around the shaft. Comparing simulations made with crushable and uncrushable grains, and analysing the particle displacement fields, provides insights into one of the mechanisms proposed for the well-known, yet not fully understood, marked shaft capacity increases developed over time by piles driven in sands.
Ciantia M, Arroyo M, O'Sullivan C, et al., 2019, Grading evolution and critical state in a discrete numerical model of Fontainebleau sand, Géotechnique, Vol: 69, Pages: 1-15, ISSN: 0016-8505
Granular materials reach critical states upon shearing. The position and shape of a critical state line (CSL) in the compression plane are important for constitutive models, interpretation of in situ tests and liquefaction analyses. It is not fully clear how grain crushing may affect the identification and uniqueness of the CSL in granular soils. Discrete-element simulations are used here to establish the relation between breakage-induced grading evolution and the CSL position in the compression plane. An efficient model of particle breakage is applied to perform a large number of tests, in which grading evolution is continuously tracked using a grading index. Using both previous and new experimental results, the discrete-element model is calibrated and validated to represent Fontainebleau sand, a quartz sand. The results obtained show that, when breakage is present, the inclusion of a grading index in the description of critical states is advantageous. This can be simply done using the critical state plane (CSP) concept. A CSP is obtained for Fontainebleau sand.
Liu D, O'Sullivan C, Carraro A, 2019, STRESS DISTRIBUTION IN TRIMODAL SAMPLES, 6th International Conference on Particle-Based Methods (PARTICLES) - Fundamentals and Applications, Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 58-67
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- Citations: 1
Nguyen C, O'Sullivan C, Otsubo M, 2018, Discrete element method analysis of small-strain stiffness under anisotropic stress states, Géotechnique Letters, Vol: 8, Pages: 1-7, ISSN: 2045-2543
This contribution assesses the influence of stress anisotropy on stiffness using discrete element method (DEM) simulations of true-triaxial tests supplemented with analytical studies. The samples considered comprised of normally consolidated random monodisperse samples. The simulations were carried out at four different mean stress levels; at each stress level, various combinations of the three principal stresses were considered. Stiffness was measured using planar wave propagation simulations. Using regression analysis it is shown that density effects can be considered using void ratio correction factors derived for isotropically compressed samples. However, a void ratio correction factor that considers coordination number is seen to be more marginally appropriate than the conventional form used in geotechnical experimental work. Material exponents that quantify the influence of each stress component on the stiffness were then determined. Analytical expressions derived from effective medium theory are less effective than the correction functions following the form used in the current experimental practice.
Kawano K, Shire T, O'Sullivan C, 2018, Coupled particle-fluid simulations of the initiation of suffusion, SOILS AND FOUNDATIONS, Vol: 58, Pages: 972-985, ISSN: 0038-0806
Otsubo M, O'Sullivan C, 2018, Experimental and DEM assessment of stress-dependency of surface roughness effect on sample shear modulus, Soils and Foundations, Vol: 58, Pages: 602-614, ISSN: 0038-0806
This contribution assesses the effect of particle surface roughness on the shear wave velocity (VS) and the small-strain stiffness (G0) of soils using both laboratory shear plate dynamic tests and discrete element method (DEM) analyses. Roughness is both controlled and quantified to develop a more comprehensive understanding than was achieved in prior contributions that involved binary comparisons of rough and smooth particles. Glass beads were tested to isolate surface roughness effects from other shape effects. VS and G0 were accurately determined using a new design configuration of piezo-ceramic shear plates. Both the experimental and the DEM results show that increasing surface roughness reduces G0 particularly at low stress levels; however, the effect is less marked at high pressures. For the roughest particles, the Hertzian theory does not describe the contact behaviour even at high pressures; this contributes to the fact that the exponent in the G0 – mean effective stress relationship exceeds 0.33 for sand particles. Particle-scale analyses show that the pressure-dependency of the surface roughness effects on G0 can be interpreted using roughness index α which enables the extent of the reduction in G0 due to surface roughness to be estimated.
Hanley KJ, Huang X, O'Sullivan C, 2018, Energy dissipation in soil samples during drained triaxial shearing, Geotechnique, Vol: 68, Pages: 421-433, ISSN: 1751-7656
The discrete-element method was used to simulate drained triaxial compression of large-scale, polydisperse numerical samples at a range of void ratios while tracing all relevant energy components. The frictional dissipation and boundary work are almost equal regardless of sample density. The volumetric work reaches a steady value at large strain. However, the distortional work increases continually as sample deformation continues post-critical state. There is a preferential orientation for frictional dissipation at around 45° to the major principal stress direction. This matches the orientation at which there is the largest number of sliding contacts. The work equations, which are fundamental in most commonly used constitutive models, are linear when plotted against deviatoric strain. The modified Cam Clay work equation substantially over-predicts the frictional dissipation for dense samples. An alternative, thermodynamically consistent work equation gives a much better description of frictional dissipation and is therefore recommended to ensure accuracy in modelling.
Gens A, Arroyo M, Butlanska J, et al., 2018, Discrete Simulation of Cone Penetration in Granular Materials, 14th International Conference on Computational Plasticity, Fundamentals and Applications (COMPLAS), Publisher: SPRINGER-VERLAG BERLIN, Pages: 95-111
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- Citations: 1
Liakas S, O'Sullivan C, Saroglou C, 2017, Influence of heterogeneity on rock strength and stiffness using discrete element method and parallel bond model, JOURNAL OF ROCK MECHANICS AND GEOTECHNICAL ENGINEERING, Vol: 9, Pages: 575-584, ISSN: 1674-7755
The particulate discrete element method (DEM) can be employed to capture the response of rock, provided that appropriate bonding models are used to cement the particles to each other. Simulations of laboratory tests are important to establish the extent to which those models can capture realistic rock behaviors. Hitherto the focus in such comparison studies has either been on homogeneous specimens or use of two-dimensional (2D) models. In situ rock formations are often heterogeneous, thus exploring the ability of this type of models to capture heterogeneous material behavior is important to facilitate their use in design analysis. In situ stress states are basically three-dimensional (3D), and therefore it is important to develop 3D models for this purpose. This paper revisits an earlier experimental study on heterogeneous specimens, of which the relative proportions of weaker material (siltstone) and stronger, harder material (sandstone) were varied in a controlled manner. Using a 3D DEM model with the parallel bond model, virtual heterogeneous specimens were created. The overall responses in terms of variations in strength and stiffness with different percentages of weaker material (siltstone) were shown to agree with the experimental observations. There was also a good qualitative agreement in the failure patterns observed in the experiments and the simulations, suggesting that the DEM data enabled analysis of the initiation of localizations and micro fractures in the specimens.
Knight C, Abdol Azis MH, O'Sullivan C, et al., 2017, Sensitivity analysis of Immersed Boundary Method simulations of fluid flow in dense polydisperse random grain packings, EPD Sciencies, Powders and Grains 2017 – 8th International Conference on Micromechanics on Granular Media, ISSN: 2101-6275
Polydisperse granular materials are ubiquitous in nature and industry. Despite this, knowledge of the momentum coupling between the fluid and solid phases in dense saturated grain packings comes almost exclusively from empirical correlations [2-4, 8] with monosized media. The Immersed Boundary Method (IBM) is a Computational Fluid Dynamics (CFD) modelling technique capable of resolving pore scale fluid flow and fluid-particle interaction forces in polydisperse media at the grain scale. Validation of the IBM in the low Reynolds number, high concentration limit was performed by comparing simulations of flow through ordered arrays of spheres with the boundary integral results of Zick and Homsy [10] . Random grain packings were studied with linearly graded particle size distributions with a range of coefficient of uniformity values (C u = 1.01, 1.50, and 2.00) at a range of concentrations (Φ ∈ [0.396; 0.681]) in order to investigate the influence of polydispersity on drag and permeability. The sensitivity of the IBM results to the choice of radius retraction parameter [1] was investigated and a comparison was made between the predicted forces and the widely used Ergun correlation [3].
Nguyen H, Otsubo M, O'Sullivan C, 2017, An appraisal of the influence of material fabric and stress anisotropy on small-strain stiffness, 8th International Conference on Micromechanics of Granular Media (Powders and Grains), ISSN: 2101-6275
© The Authors, published by EDP Sciences, 2017. This paper examines the effect of a non-isotropic, true triaxial stress state on soil stiffness using discrete element method (DEM) simulations. Samples of uniform spheres with a very stable face centred cubic (FCC) are considered to isolate the effect of stress from stress-induced fabric changes. At the same time the anisotropic nature of the lattice fabric enables the effect of fabric on the observed responses to be explored. The elastic or small strain stiffness was determined by applying small amplitude displacement perturbations to the samples and measuring the resultant shear wave velocity. Two different mean stress levels were considered and at both stress levels the magnitudes of the three principal stresses were varied. The data obtained confirm that the stresses in direction of wave propagation and shear wave oscillation have a measurable influence on shear modulus values. The extent of sensitivity depends on the material fabric. The stress component orthogonal to the plane of wave motion has, however, a less marked effect on shear.
Kawano K, Shire T, O'sullivan C, 2017, Coupled DEM-CFD Analysis of the Initiation of Internal Instability in a Gap-Graded Granular Embankment Filter, Powders and Grains 2017 – 8th International Conference on Micromechanics on Granular Media, ISSN: 2101-6275
© The Authors, published by EDP Sciences, 2017. Internal instability is a form of internal erosion that can occur in embankment dams or flood embankments where the finer fraction of the material is washed out under the action of seepage flow; if undetected this process can progress to cause embankment collapse. Gap-graded materials are particularly susceptible. Skempton and Brogan [1] proposed that a key contributor to instability is the reduced stress transmitted by the finer fraction and that the magnitude of this reduced stress could be inferred from the hydraulic gradients observed at the initiation of particle migration in experiments. Here Skempton and Brogan's hypothesis is assessed at the particle scale using a discrete element method (DEM) model coupled with computational fluid dynamics (CFD). This contribution discusses validation of the coupled DEM-CFD software prior to describing the simulation of a permeameter experiment. The simulation generated particlescale data at the initiation of instability by considering a gap-graded sample subject to at a hydraulic gradient of 1.0 (upward flow). The results provide insight into the instability mechanism, most notably showing that while the particles that move under seepage flow do indeed transmit relatively small effective stress, a finite proportion of the particles that move transfer relatively large stresses.
Hanley KJ, Huang X, O'Sullivan C, 2017, Comparing the effects of interparticle friction coefficient and intermediate stress ratio on critical-state DEM simulations using Delaunay triangulations, Powders and Grains 2017 – 8th International Conference on Micromechanics on Granular Media, ISSN: 2101-6275
© The Authors, published by EDP Sciences, 2017. Strong force chains form when any granular material is subjected to load. A prior study used Delaunay triangulations to investigate the role of interparticle friction coefficient, μ, in stabilising the strong force chains [1]. In this follow-on paper, the effects of μ and the intermediate stress ratio, b, are compared. Numerical samples were sheared triaxially until critical state was attained. The contact networks and Delaunay triangulations of the particle centroids were both obtained at the end of each simulation. As μ is increased, the numbers of contacts in the contact networks decrease consistently. The numbers of edges, faces or tetrahedra in the Delaunay triangulations all increase with increasing μ up to 0.25 and become approximately constant thereafter. Changing b has no significant effect. The percentage of faces in the triangulation comprising three contacts shows a linearly-decreasing trend with increasing angle of shearing resistance. This is because only orthogonal loads are applied. Triangular structures require larger lateral supporting forces to maintain their stability than columnar structures when subjected to an axial load; hence, σ3′ is expected to be larger relative to σ1′ when triangular motifs are more prevalent. An increased proportion of triangular structures therefore leads to a lower Φ'cv′.
Otsubo M, O'Sullivan C, Hanley KJ, et al., 2017, Influence of packing density and stress on the dynamic response of granular materials, Granular Matter, Vol: 19, ISSN: 1434-7636
Laboratory geophysics tests including bender elements and acoustic emission measure the speed of propagation of stress or sound waves in granular materials to derive elastic stiffness parameters. This contribution builds on earlier studies to assess whether the received signal characteristics can provide additional information about either the material’s behaviour or the nature of the material itself. Specifically it considers the maximum frequency that the material can transmit; it also assesses whether there is a simple link between the spectrum of the received signal and the natural frequencies of the sample. Discrete element method (DEM) simulations of planar compression wave propagation were performed to generate the data for the study. Restricting consideration to uniform (monodisperse) spheres, the material fabric was varied by considering face-centred cubic lattice packings as well as random configurations with different packing densities. Supplemental analyses, in addition to the DEM simulations, were used to develop a more comprehensive understanding of the system dynamics. The assembly stiffness and mass matrices were extracted from the DEM model and these data were used in an eigenmode analysis that provided significant insight into the observed overall dynamic response. The close agreement of the wave velocities estimated using eigenmode analysis with the DEM results confirms that DEM wave propagation simulations can reliably be used to extract material stiffness data. The data show that increasing either stress or density allows higher frequencies to propagate through the media, but the low-pass wavelength is a function of packing density rather than stress level. Prior research which had hypothesised that there is a simple link between the spectrum of the received signal and the natural sample frequencies was not substantiated.
Lopera Perez JC, Kwok CY, O'Sullivan C, et al., 2017, Erratum to “Assessing the quasi-static conditions for shearing in granular media within the critical state soil mechanics framework” (Soils and Foundations (2016) 56(1) (152–159) (S0038080616000147) (10.1016/j.sandf.2016.01.013)), Soils and Foundations, Vol: 57, Pages: 496-498, ISSN: 0038-0806
© 2017 The publisher regrets that the inertial number values were miscalculated. The internal number (I) values listed on Table 1 and in the legend entries of Figs. 3, 4, 5(c), 6(a) and 7(a) should be revised as follows: [Table presented] The revised numbers should be taken to replace the original values that are given in the discussion in the manuscript text. For clarity, Figs. 5a, 5b, 5d, 6 and 7 are replotted: [Table presented] Regarding the conclusions presentated in Section 5 of the paper the following revised observations should be noted: 1. A clear dependancy of the dilatancy on I was found for I > 3.2e−4.2. An indistinguishable response was found for I < 7.9e−5.3. The proposed upper limit for quasi-static simulations should be taken as I ≤ 7.9e−5.4. This limit is relatively conservative and represents a lower bound to the values given in the literature (MiDi, 2003; da Cruz et al., 2005; Koval et al., 2009; Azema and Radjai, 2014).5. The limit is in agreement with the observations of Modenese (2013) who noted a sensitivity of the critical state parameters to I at I values as low as 1−4.The publisher would like to apologise for any inconvenience caused.
Perez JCL, Kwok CY, O'Sullivan C, et al., 2017, Assessing the quasi-static conditions for shearing in granular media within the critical state soil mechanics framework (Vol 56, pg 152, 2016), SOILS AND FOUNDATIONS, Vol: 57, Pages: 496-498, ISSN: 0038-0806
Taylor HF, O'Sullivan C, Sim W, et al., 2017, Sub-particle-scale investigation of seepage in sands, Soils and Foundations, Vol: 57, Pages: 439-452, ISSN: 0038-0806
While seepage poses significant challenges to many geotechnical projects and hydraulic conductivity is a key soil property, the fundamental pore-scale understanding of the water flow in soil is poor. The seepage velocities considered in geotechnical engineering are area-averaged flow rates and their relation to the actual fluid velocity is unclear. Some of the predictive formulae for sand currently used in engineering practice were developed using simplified particle-scale analytical models whose validity is not well-established. Recent advances in modelling and imaging enable these uncertainties associated with seepage to be addressed and this paper proposes a first principles simulation approach in which the flow in the void space is modelled by applying Computational Fluid Dynamics (CFD) to void geometries obtained using X-ray micro-Computed Tomography (microCT). The model was verified by comparing it to hydraulic conductivity data from laboratory permeameter tests on the same materials. The generated data provide significant sub-particle-scale insight into fluid velocities and head loss. The results are used to show that the existing models for predicting hydraulic conductivity struggle to account for the full range of particle variables and fail to explain the true governing variables, which relate to the micro-scale properties of the void space.
Otsubo M, O'Sullivan C, Hanley KJ, et al., 2017, The influence of particle surface roughness on elastic stiffness and dynamic response, GEOTECHNIQUE, Vol: 67, Pages: 452-459, ISSN: 0016-8505
Discrete-element method (DEM) simulations of planar wave propagation are used to examine the effect of particle surface roughness on the stiffness and dynamic response of granular materials. A new contact model that considers particle surface roughness is implemented in the DEM simulations. Face-centred cubic lattice packings and random configurations are used; uniform spheres are considered in both cases to isolate fabric and contact model effects from inertia effects. For the range of values considered here surface roughness caused a significant reduction in stiffness, particularly at lower confining stresses. The simulations confirm that surface roughness effects can at least partially explain the value of the exponent in the relationship between stiffness and mean confining stress for an assembly of spherical particles. Frequency domain analyses showed that the maximum frequency transmitted through the sample is reduced when surface roughness is considered. The assumption of homogeneity of stress and contacts in analytical micromechanical models is shown to lead to an overestimation of stiffness.
Huang X, Hanley K, O'Sullivan C, et al., 2017, Implementation of rotational resistance models: a critical appraisal, Particuology, Vol: 34, Pages: 14-23, ISSN: 1674-2001
Contact models that simulate rotational resistance at the particle contacts have been proposed as a means to capture the shape effect in DEM simulations. This contribution critically explores some of the key issues relating to implementation of rotational resistance models; these include the need for physically meaningful model parameters, the impact of the model on the overall numerical stability / critical time increment for the DEM model, model validation and assessment of model performance relative to real physical materials. The discussion is centred around a rotational resistance model that captures the resistance provided by interlocking asperities on the particle surface. An expression for the maximum permissible integration timestep to ensure numerical stability is derived for DEM simulations when rotational resistance is incorporated. Analytical solutions for some single-contact scenarios are derived for model validation. The ability of this type of model to provide additional fundamental insight into granular material behaviour is demonstrated by using particle-scale analysis of triaxial compression simulations to examine the roles that contact rolling and sliding have on the stability of strong force chains.
Cavarretta I, O'Sullivan C, Coop MR, 2017, The relevance of roundness to the crushing strength of granular materials, GEOTECHNIQUE, Vol: 67, Pages: 301-312, ISSN: 0016-8505
Otsubo M, O'Sullivan C, Shire T, 2017, Empirical assessment of the critical time increment in explicit particulate discrete element method simulations, Computers and Geotechnics, Vol: 86, Pages: 67-79, ISSN: 0266-352X
This contribution considers the critical time increment (〖∆t〗_crit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The 〖∆t〗_crit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, 〖∆t〗_crit is shown to depend on the particle mass (m), the maximum contact stiffness (Kmax), and the maximum particle coordination number (CN,max). Empirical expressions relating 〖∆t〗_crit to m, Kmax, and CN,max are presented; while strictly only valid within the range of simulation scenarios considered here, these can inform DEM analysts selecting appropriate 〖∆t〗_crit values.
Huang X, O'Sullivan C, Zhang Z, et al., 2017, Exploring the Undrained Cyclic Behaviour of Sand Using DEM, 7th International Conference on Discrete Element Methods (DEM), Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 757-765, ISSN: 0930-8989
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- Citations: 4
Kareh KM, O'Sullivan C, Nagira T, et al., 2016, Dilatancy in semi-solid steels at high solid fraction, Acta Materialia, Vol: 125, Pages: 187-195, ISSN: 1873-2453
The study of mushy-zonedeformation in steels is important forlimitingdefect formation in continuous casting. Here, we use in situsynchrotron radiography to quantify the shear deformation mechanisms of an equiaxedcarbon steel at asolid fraction >0.9 and to understand how these mechanisms lead to casting defects. We show that the grain assembly undergoes shear-induced dilation(Reynolds’dilatancy)which opens liquid-filled fissures andcracksat high solid fraction. We further show a complex interaction between grain rearrangement, grain deformation and local coarsening, where rearrangement reducesthe grain-grain contact area andcoordination number which alters the stress networkand also drives coarsening as grains move apart.
Shire TC, O'Sullivan C, 2016, A network model to assess base-filter combinations, Computers and Geotechnics, Vol: 84, Pages: 117-128, ISSN: 1873-7633
Granular filters retain base material within the narrowest constrictions of their void network. A direct comparison of the base material particle size distribution (PSD) and the filter constriction size distribution (CSD) cannot easily be used to assess filter-base compatibility. Here a conceptually simple random-walk network model using a filter CSD derived from discrete element modelling and base PSD is used to assess filter-base compatibility. Following verification using experimental data the model is applied to assess empirical ratios between filter and base characteristic diameters. The effects of filter density, void connectivity and blocking in the first few filter layers are highlighted.
Gens A, Arroyo M, Butlanska J, et al., 2016, SIMULATION OF THE CONE PENETRATION TEST: DISCRETE AND CONTINUUM APPROACHES, AUSTRALIAN GEOMECHANICS JOURNAL, Vol: 51, Pages: 169-182, ISSN: 0818-9110
Gens A, Arroyo M, Butlanska J, et al., 2016, SIMULATION OF THE CONE PENETRATION TEST: DISCRETE AND CONTINUUM APPROACHES, AUSTRALIAN GEOMECHANICS JOURNAL, Vol: 50, Pages: 169-182, ISSN: 0818-9110
Otsubo M, O'sullivan C, Hanley KJ, et al., 2016, The influence of particle surface characteristics on elastic stiffness and dynamic response, Géotechnique, ISSN: 0016-8505
Discrete element method (DEM) simulations of planar wave propagation are used to examine theeffect of particle surface roughness on the stiffness and dynamic response of granular materials. Anew contact model that considers particle surface roughness is implemented in the DEM simulations.Face-centred cubic lattice packings and random configurations are used; uniform spheres areconsidered in both cases to isolate fabric and contact model effects from inertia effects. For the rangeof values considered here surface roughness caused a significant reduction in stiffness, particularly atlower confining stresses. The simulations confirm that surface roughness effects can at least partiallyexplain the value of the exponent in the relationship between stiffness and mean confining stress foran assembly of spherical particles. Frequency domain analyses showed that the maximum frequencytransmitted through the sample is reduced when surface roughness is considered. The assumption ofhomogeneity of stress and contacts in analytical micromechanical models is shown to lead to anoverestimation of stiffness.
Fonseca J, Nadimi S, Reyes-Aldasoro CC, et al., 2016, 10.1016/j.sandf.2016.08.007, Soils and Foundations, ISSN: 0038-0806
Shire TC, O'Sullivan C, 2016, Constriction size distributions of granular filters: a numerical study, Geotechnique: international journal of soil mechanics, Vol: 66, Pages: 826-839, ISSN: 0016-8505
The retention capability of granular filters is controlled by the narrow constrictions connecting the voids within the filter. The theoretical justification for empirical filter rules used in practice includes consideration of an idealised soil fabric in which constrictions form between co-planar combinations of spherical filter particles. This idealised fabric has not been confirmed by experimental or numerical observations of real constrictions. This paper reports the results of direct, particle-scale measurement of the constriction size distribution (CSD) within virtual samples of granular filters created using the discrete-element method (DEM). A previously proposed analytical method that predicts the full CSD using inscribed circles to estimate constriction sizes is found to poorly predict the CSD for widely graded filters due to an over-idealisation of the soil fabric. The DEM data generated are used to explore quantitatively the influence of the coefficient of uniformity, particle size distribution and relative density of the filter on the CSD. For a given relative density CSDs form a narrow band of similarly shaped curves when normalised by characteristic filter diameters. This lends support to the practical use of characteristic diameters to assess filter retention capability.
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