Discrete Element Modeling Approach Research Articles

Influence of Type of Sleeper–Ballast Interface on the Shear Behaviour of Railway Ballast: An Experimental and Numerical Study

The shear resistance at the sleeper–ballast interface of a ballasted track is an important contributor in maintaining track stability under faster and heavier axle loads where the ballast undergoes significant lateral sliding. Different types of sleeper–ballast interfaces based on the type of sleeper arrangements, such as concrete sleepers, timber sleepers, and under sleeper pads (USPs) attached to the concrete sleepers influence the lateral stability of railway tracks. Therefore, in this study the shear and degradation behaviour of ballast at concrete–ballast, timber–ballast, and USP–ballast interfaces were examined in the laboratory using large-scale direct shear tests under 60 kPa normal stress. The use of waste materials in the construction of civil infrastructure is gaining a lot of interest in the engineering community. Therefore, in addition to commercial USPs manufactured using raw materials, recycled USPs manufactured from granulates of end-of-life rubber tyres were also tested in this study. The discrete element modelling (DEM) approach was used to predict the shear behaviour of ballast at 30, 90, 120, 150, and 180 kPa normal stresses. The bonded particle model (BPM) was adopted in the DEM to simulate the effects of particle breakage during shearing. The results exhibited that both commercial and recycled USPs significantly improve the shear resistance at the sleeper–ballast interface while reducing particle degradation compared to concrete and timber sleeper interfaces.

An improved machine learning approach for predicting granular flows

Granular flow is widely practised in many industry processes. The previous prediction methods of granular flow are limited in efficiency, including conventional Discrete Element Modelling (DEM) where direct computation of particle collisions is very time-consuming; and recent machine learning (ML) approach where particle positions were straight predicted and particle–particle and particle–wall collisions were not considered separately, likely compromising the prediction accuracy. In this study, an improved ML approach is developed for predicting granular flows efficiently in terms of computational speed and accuracy. In the proposed ML approach, inspired by Newton’s second law’s concept – from particle acceleration to calculate velocity and then position, a new continuous convolutional neural network (CNN) is established to predict the particles’ accelerations first based on the particle–particle and particle–wall collisions separately, and the particle accelerations are used for calculating particle velocities and finally particle positions. The ML approach is applied to a typical granular flow - particle packing for demonstration. A dataset of 100 scenes of DEM simulations in one scenario is established for network training and examination. The results show that, in long-sequence predictions, the accuracy of the ML approach is three times higher than the previous ML approach. The effects of hyperparameters in the network are quantified. Then the ML approach with the optimized hyperparameters is used in additional three scenarios for further examining the prediction effectiveness. It is indicated that the improved ML approach can satisfactorily capture the morphology of granular flows under three new different scenarios; and the computational cost is only one-seventh compared to the DEM approach under the present conditions. The ML approach provides a simple and time-effective tool for simulating granular flows.

Grain-scale analysis of proppant crushing and embedment using calibrated discrete element models

Proppant crushing and embedment in hydraulically-induced fractures is a major drawback to the recovery of unconventional oil/gas and geothermal energy production. This study provides a grain-scale analysis of the fracture evolution mechanisms of proppant crushing, rock fracture damage during proppant embedment, the influence of realistic reservoir/fracture fluid on proppant embedment, and the behaviour of proppant packs subjected to in-situ stresses using a discrete element modelling (DEM) approach. The results of this study reveal that the selection of an appropriate proppant type based on the nature of the reservoir formation plays a vital part in quantifying the degree of proppant crushing and embedment within fractures. The utilisation of frac-sand proppants instead of ceramic proppants in shallow soft sedimentary-based siltstone formations reduces proppant embedment up to 88%. However, whatever the depth of the fracture, the injection of ceramic proppants into granite-based geothermal formations is preferred to that of frac-sand proppants due to their lower proppant embedment and greater crush resistance. DEM analysis detected rock-spalling during the proppant embedment process, which ultimately led to the initiation of tensile-dominant secondary fractures in rocks. Fracture initiation, propagation, and coalescence during proppant crushing are analysed using calibrated DEM proppant-rock assemblies. Importantly, this study reveals that the saturation of formation rocks with fracturing/reservoir fluids may cause a significant increase in proppant embedment. Furthermore, proppant crushing, embedment, and re-arrangement mechanisms in proppant packs with different proppant distributions are analysed in this comprehensive numerical study.

A new discrete element modelling approach to simulate the behaviour of dense assemblies of true polyhedra

A new molecular dynamics-like modelling approach aimed at simulating the mechanical behaviour of true polyhedra dense assemblies is presented. Thanks to an improved version of the Gilbert-Johnson-Keerthi contact detection algorithm called GJK − TD, this approach involves no edge or corner rounding and accounts for multipoint face − face or edge − face contacts between any set of two particles. Furthermore, torques equations are simply and efficiently solved using an improved leap-frog Verlet non-iterative method suggested by Omelyan [I.P. Omelyan, Molecular Simulation, 22 : 3, 213–236 (1999)], in which no periodic renormalization of the quaternions is necessary. The potential of this new discrete element approach is then highlighted by simulating the gravity packing of frictionless polyhedra and the gavity flow of frictional polyhedra down an incline, and comparing the results with those reported in the literature. Of particular interest in the stationary flow regime, a linear decrease of the bulk solid fraction and a power law decrease of the bulk coordination number with increasing inertial number are observed, thus generalizing to polyhedra these observations initially made with disks in plane shear flow by da Cruz and co-workers [F.da Cruz, S. Emam, M. Prochnow, J.N. Roux and F. Chevoir, Phys. Rev. E 72, 021309, (2005)]. Beyond this regime, in the collisional regime, the granular temperature was found to achieve its maximum a few particle diameter above the rough bottom, suggesting the localization of significant particle agitation close to the flowing bed.

Discrete element modeling of aggregate shape and internal structure effects on Weibull distribution of tensile strength

Many soil processes and functions, including carbon storage, water and element cycling, and crop productivity, are directly or indirectly affected by soil aggregates. As a key property, aggregate tensile strength is usually quantified by the Weibull distribution. This distribution was found to depend on soil texture, organic matter content, and aggregate shape; however, effects of cementing agents (i.e., clay mineral and organic compounds) on aggregate tensile strength cannot be empirically studied independent of shape. The objective was to apply Discrete Element Modeling (DEM) to simulate the rupture of soil aggregates of different shapes but the same assumed distributions of cementing agents. The hypothesis was that the Weibull modulus of aggregate tensile strength could be used to describe the heterogeneity of the particle binding forces within the aggregate. Multiple DEM simulations of aggregate rupture were carried out for sets of randomly generated binding force distributions between particles of the same diameter. Aggregate properties and shapes were obtained from those observed in arable Gleyic Cambisol topsoil from plots with and without vegetation of a soil compaction trial; additional aggregate shapes were simulated to increase the predictive range. The simulation results showed that (i) the sensitivity of Weibull modulus of aggregate tensile strength to the heterogeneity of particle binding force distribution increased with aggregate sphericity, (ii) the value of the Weibull modulus decreased with increasing heterogeneity of this distribution, and (iii) internal heterogeneity also reduced the crack surface area produced by aggregate rupture. Results corresponded to friability theory implying that small values of Weibull modulus indicated more complex soil structural organization. The DEM simulations could help explaining complex interactions between aggregate shape cementing agents and stability. Our DEM approach also uncovered the importance of Weibull modulus to assess structural features of soil aggregates and to describe the heterogeneity of the particle binding forces within the aggregate.

Coupled 3D numerical model for a landslide-induced impulse water wave: A case study of the Fuquan landslide

Large impulse waves are generated when a highly mobilized landslide impacts a water body along the runout path. On August 27, 2014, a massive landslide occurred in Fuquan, Guizhou, China and induced an impulse wave upon contact with a quarry lake. The landslide and its associated impulse wave were a multiphase and multicomponent mixture that collectively destroyed two villages. The present study provides insights into multiphase dynamic analysis by employing an existing 3D coupled discrete element modeling and computational fluid dynamics approach to model a case study of the Fuquan landslide and its impulse wave. EDEM and Fluent were two-way coupled by an application programming interface, which transferred data between the models to simulate subaerial movement and impulse wave generation. The simulated results indicate a maximum velocity of 31.7 m/s achieved by the subaerial movement and a runout duration of 39 s. The detached mass entered the quarry lake at a velocity of 24.3 m/s, at t = 7.1 s after the landslide initiation. Energy was transferred between the sliding mass and lake water, and the generated water wave rushed toward the opposite slope. The generated wave had a run-up of 28.4 m and traveled approximately 90 m in the lateral direction, with a maximum dynamic pressure of 3.03 MPa. Qualitative validation of the present model was performed using Fritz's experimental setup for wave generation, and the velocity evolution was physically verified. This study provides calibrated parameters for the forward simulation of similar cases of landslide-induced impulse water waves and related hazard zonation.

Hybrid multi-zonal compartment modeling for continuous powder blending processes

To modernize drug manufacturing, the pharmaceutical industry has been moving towards implementing emerging technologies to enhance manufacturing robustness and process reliability for production of regulation compliant drug products. Although different science and risk based technologies, like Quality-by-Design, have been used to illustrate their potential, there still exist some underlying obstacles. Specifically, for the production of oral solid drug products, an in-depth process understanding, and predictive modeling of powder mixing in continuous powder blenders is one such major obstacle and originates from the current limitations of the experimental and modeling approaches. Though first principle based discrete element modeling (DEM) approach can address the above issues, it can get very computationally intensive which limits its applications for predictive modeling. In the proposed work, we aim to address this limitation using a multi-zonal compartment modeling approach, which is constructed from DEM. The approach provides a computationally efficient and mechanistically informed hybrid model. The application of the proposed approach is first demonstrated for a periodic section of the blender, followed by its extension for the entire continuous powder blender and the obtained model predictions are validated. The proposed approach provides an overall assessment of powder mixing along axial and radial directions, which is an important requirement for the quantification of blend uniformity. Given the low computational cost, the developed model can further be integrated within the predictive flowsheet model of the manufacturing line.

Assessment of a tomography-informed polyhedral discrete element modelling approach for complex-shaped granular woody biomass in stress consolidation

The design of handling equipment for granular biomass primarily requires experiments. Discrete element models (DEM) can provide designers with detailed insight into the behaviour of granular materials. However, granular biomass comprising complex-shaped particles is difficult to model with DEM. A tomography-informed DEM approach and an exhaustive assessment of the ability of the approach to predict the bulk behaviour of milled pines using experimental data is presented. Nano-CT scan was conducted to obtain 3D particle surface geometries as the basis for particle shape approximation by a polyhedral model and a sphero-polyhedral model. These models were applied in the simulation of a compressibility test. Our parametric study showed that particle Young's modulus and restitution coefficient are the two main properties influencing the simulated bulk behaviour of the DEM particles and that the level of approximating DEM particle shape for real particles is critical for accurately replicating the bulk behaviour of milled pines. The polyhedral model demonstrated better suitability than its sphero-polyhedral counterpart for modelling pine particles. The polyhedral model calibrated in a compressibility test was then applied in the simulations of a friction test without additional parameter tuning. Interlocking was dominant in the shear of bulk pine particles. Remarkably, the polyhedral model predicted the frictional behaviour of the pine particles when compared to the experimental results. The limitations of the model, as well as possible ways for enhancement, are discussed. This work provided novel insights into the suitability of complex-shaped DEM models for granular woody biomass.

DEM simulation of the thermo-geomechanical effect of recycled concrete aggregate assemblies in geothermal pavement bases

This paper studies the discrete element modeling (DEM) of the thermal-geomechanical effect of recycled concrete aggregate (RCA) assemblies when harnessing renewable geothermal energy from pavement bases. This research study aims to simulate the behavior of RCA under repeated load triaxial test (RLT) at temperatures varying from 20 °C to 80 °C, to simulate temperature effects when harnessing geothermal energy from pavements. The DEM approach was used to simulate unsaturated soil considering interparticle water meniscus and the variation in its force due to the temperature fluctuation. In this research study, RCA samples with different particle size distributions were simulated under RLT test condition for various temperature conditions. According to the macro-geomechanical results, the resilient modulus (MR), porosity, and accumulated strain of samples showed different trends under varying temperatures. Comparing the micro-geomechanical behavior of the samples indicated that matric suction decreased with increasing temperature. Furthermore, the particle scale matric suction was found to be affected by the size ratio of the contacted particles. It was observed that varying the size ratio between 1 and 4 led to a higher average matric suction. The evolution of coordination number (CN), contact normal and contact normal force indicated that samples with higher sand content experienced decrease in CN and magnitude of contact normal by increasing temperature. Meanwhile, samples with lower sand content tended to have an increased CN and magnitude of contact normal in the direction of anisotropy at increased temperatures. An equation was also proposed to predict MR based on matric suction and the ratio of fine over coarse content, based on the RCA particle sizes.

Simulation of the process of interaction between the vehicle and snow in the environment of DEM and MBD-systems

The problem of increasing the mobility of tractors on snow in our country is very important. This is due to the long duration of the snow cover, primarily in those regions that are of great national and economic importance in terms of mining. There are many methods to increase the mobility of the vehicle, but all of them are associated with increased traction, as well as bearing characteristics of the wheel. The question of calculating the resistance to movement on the part of the body parts submerged in the snow, as well as transmission and engine for a long time did not receive sufficient attention, despite the fact that their contribution to the overall resistance to movement can reach 60%. In this article the existing methods of calculation and modeling of the value of resistance to movement on the side of housing parts are considered, their advantages and disadvantages are given. The design of a soil canal to study the movement of large-scale models of cars in the snow is considered, and the conclusion is made as to the feasibility of using this method at the present time. The paper also suggests a new method of drag calculation based on the joint use of discrete element modelling (DEM) and multibody dynamics (MBD) software packages. This approach allows both realistically simulate snow due to the discrete element modeling approach, and enter into the model the values of loads on the suspension, traction force, etc. through the use of MBD. The article deals with the technique of modeling the interaction of the body with snow in the EDEM package of DEM Solutions Ltd. The scheme of interaction between DEM and MBD-packages on the example of EDEM and MSC Adams software is described, as well as the technique of using Adams/Co-simulation Interface (ACSI).

External signal preservation in halokinetic stratigraphy: A discrete element modeling approach

Abstract Subsurface salt movement in the absence of external tectonic forces can affect contemporaneous sediment deposition, mask allocyclic signals, and deform older strata. We used a discrete element model (DEM) to better understand salt-related modification of a sedimentary sequence with an increasing sedimentation rate. This permitted quantification of thinning rates and analysis of the lateral extent of synkinematic layers. Results show realistic evolution of salt-related faults, defining two salt-withdrawal basins, beyond which strata are undeformed. Thinning of stratigraphy is four times greater between the salt flank and crest than between the undeformed zone and flank, confirming an intense zone of halokinetic modulation adjacent to the diapir. Early, slowly aggrading layers are isolated within the salt-withdrawal basin and strongly influenced by salt growth, whereas later, quickly aggrading layers are more laterally extensive, matching inferences made from subsurface and outcrop data. Halokinetic modulation reduces up the stratigraphic section, mirroring observations around the Pierce diapirs, in the North Sea, offshore UK. Our DEM provides quantitative insights into the dynamic interplay between halokinetic and allocyclic controls on salt-stratigraphic relationships.

Shake table testing of a rocking podium: Results of a blind prediction contest

AbstractRocking motion is sensitive to the boundary and initial conditions of a rocking structure, making experiments nonrepeatable. Thus, the claims that numerical rocking motion models are not only inaccurate but that all rocking structures behave unpredictably. Hence, rocking is not used as a seismic design approach. This paper revisits the issue of rocking motion unpredictability. Seismic behavior of structures is inherently stochastic, because the loading is stochastic. Therefore, the question of interest is not whether models can predict the seismic response to a single ground motion, but if the statistical characteristics of the ensemble of responses to a set of ground motions that define the seismic hazard can be predicted. For this purpose, a rocking podium, which is a three‐dimensional structure comprising an aluminum slab supported by four tubular steel columns, was tested on a shake table excited by two sets of 100 consistently generated ground motions. It was found that the cumulative distribution function (CDF) of the experimentally obtained displacements is statistically stable. Next, a blind prediction contest was organized. The contestants were invited to predict the CDFs of the slab lateral displacement. They were able to predict the slab displacement CDF relatively well. Both finite element and discrete element modeling approaches were used, but no clear pattern emerged as it was found that the performance of either approach depends on the input parameters used and the assumptions made. It was also observed that the contestants who did not use Rayleigh damping in their models produced better predictions.

3D discrete analysis of damage evolution of hard rock under tension

Geomechanical studies largely focus on failure and deformation processes of hard rock under compression. However, damage evolution during tensile loading conditions is not well understood in terms of revealing the local deformations. The subject of this work is discrete analysis of strain localization related to microcracking process under tensile stresses. For this purpose, a three-dimensional discrete element modeling approach is used to calibrate the mechanical responses of Forsmark granite as a typical example of hard rock. A series of uniaxial/triaxial compressive and direct tensile test simulations are initially performed on the numerical samples to ensure that the calibrated model represents accurately the mechanical failure process of the real rock in terms of failure and stress-strain relationship. Subsequently, a detailed micromechanical analysis is carried out on the numerical samples under uniaxial tensile stress loading condition. The model results show that microcracks emerge at approximately 62.5% of the peak stress. At 87.5% of the yielding point, the damage related to the diffuse microcracking propagates irrepressibly and the strain localizes in specific regions within the numerical sample which indicates the location of a macro-fracture that develops after the failure. Here, the displacement fields are also calculated during the propagation of the damage. Specifically during the early stages of the loading, the flow directions of the displacement vectors form a subhorizontal split line approximately in the center of the sample, which might also predict the location of the forthcoming damage zone. These results may provide a fundamental basis on the evolution of tensile damage process related to microcracking taking place in hard rock where many underground applications are performed.

Discrete element modeling for continuous powder feeding operation: Calibration and system analysis.

Research emphases on extensive experimental studies and modeling efforts have been on the rise for the development of accurate predictive models of pharmaceutical unit operations and 'digital-twin' framework for continuous manufacturing lines. These exhaustive studies have been conducted at different process conditions to acquire comprehensive knowledge of effects of process parameters on the overall process dynamics. However, there still lacks a detailed understanding of material property effects of pharmaceutical powders on process operation. To address this issue, a discrete element modeling (DEM) approach combined with material calibration is applied for simulation of feeder unit to obtain particle-level insight into effects of material properties on feeder performance with focus on particle flow and powder mixing within the feeder unit. Bulk calibration is implemented to accurately represent powder material properties within the DEM framework. Different refill situations are simulated using DEM to observe powder mixing, measured at the outlet. Feeder DEM simulations are further applied to understand correlations of material properties on feeder operation. These studies provide a detailed physical insight and particle-scale information into the powder mechanics during powder feeding operation.

A Combined Geometric Morphometric and Discrete Element Modeling Approach for Hip Cartilage Contact Mechanics

Finite element analysis (FEA) provides the current reference standard for numerical simulation of hip cartilage contact mechanics. Unfortunately, the development of subject-specific FEA models is a laborious process. Owed to its simplicity, Discrete Element Analysis (DEA) provides an attractive alternative to FEA. Advancements in computational morphometrics, specifically statistical shape modeling (SSM), provide the opportunity to predict cartilage anatomy without image segmentation, which could be integrated with DEA to provide an efficient platform to predict cartilage contact stresses in large populations. The objective of this study was, first, to validate linear and non-linear DEA against a previously validated FEA model and, second, to present and evaluate the applicability of a novel population-averaged cartilage geometry prediction method against previously used methods to estimate cartilage anatomy. The population-averaged method is based on average cartilage thickness maps and therefore allows for a more accurate and individualized cartilage geometry estimation when combined with SSM. The root mean squared error of the population-averaged cartilage geometry predicted by SSM as compared to the manually segmented cartilage geometry was 0.31 ± 0.08 mm. Identical boundary and loading conditions were applied to the DEA and FEA models. Predicted DEA stress distribution patterns and magnitude of peak stresses were in better agreement with FEA for the novel cartilage anatomy prediction method as compared to commonly used parametric methods based on the estimation of acetabular and femoral head radius. Still, contact stress was overestimated and contact area was underestimated for all cartilage anatomy prediction methods. Linear and non-linear DEA methods differed mainly in peak stress results with the non-linear definition being more sensitive to detection of high peak stresses. In conclusion, DEA in combination with the novel population-averaged cartilage anatomy prediction method provided accurate predictions while offering an efficient platform to conduct population-wide analyses of hip contact mechanics.

Mechanical controls on structural styles in shortening environments: a discrete-element modelling approach

AbstractIt has long been recognized that the structures that accommodate shortening within fold-and-thrust belts exhibit a wide variety of styles that reflect the mechanical behaviour of the stratigraphic units that are being deformed. The ability to characterize these different structural styles, and to understand the factors that control their variability, is essential to many applications, including petroleum geology, earthquake hazard assessment and regional geological studies. The relative contributions of different aspects of the mechanical stratigraphy and boundary conditions to determining fault-related folding style are investigated through the use of the discrete-element modelling (DEM) method in this study. Modelling emergent contractional structures within a shortening wedge with this method demonstrates that (a) The major different styles of shortening structures can all be reproduced under different mechanical circumstances within the range of realistic mechanical conditions, and (b) Different aspects of the mechanics of the deforming rock units (for example, peak strength, strain weakening, layer strength anisotropy) exert various degrees of control on the styles of structures that emerge from the models as shortening progresses. These analyses inform our understanding of the relative importance of these different factors in determining the style of structures which accommodate shortening in different fold-and-thrust belt systems.

Investigating the Effect of Aggregate Characteristics on the Macroscopic and Microscopic Fracture Mechanisms of Asphalt Concrete at Low-Temperature.

The low-temperature crack of asphalt concrete is considered to be one of the main deteriorations in asphalt pavements. However, there have been few studies on the composite effects of the aggregate characteristics and fracturing modes on the low-temperature cracking of asphalt concrete. Hence, the edge cracked semi-circular bend tests and the discrete element modeling approaches are combined to investigate the effect of the aggregate contents, aggregate morphological features and aggregate distributions on the fracture behavior of asphalt concrete in different fracturing modes at different temperatures. The results show that the fracture toughness and the crack extended time reduce with the increasing aggregate orientation and flatness and the decreased aggregate content. The effect of aggregate flatness is nonlinear, and its reduction trend grows gradually with the increasing flatness. The total number of failed contacts is reduced with the increasing aggregate orientation and flatness, particularly at 10 °C. The number of failed contacts that occurred in the aggregate–mastic interface in Quasi-Mode II fracturing is slightly higher than that in other fracturing modes. The aggregate distribution in the crack initiation zone greatly influenced the crack resistance, particularly at 10 °C. The research is beneficial to better understand the fracture mechanisms of asphalt concrete at low-temperature.

Assessment of the predictive capabilities of discrete element models for flexible rockfall barriers

This paper addresses the use of discrete element modeling approaches for predicting the impact response of flexible rockfall protection barriers. In this purpose, two different models are considered and their results are compared to detailed results from full-scale impact experiments. The studied barrier is a prototype made from a 4-contacts ring net and having a 270 kJ nominal capacity. The two discrete elements method models, developed by separate entities with different codes (Yade-DEM and GENEROCK), use different models for the ring net, the cables and cable-net connections, while other structural elements are modelled the same way : posts, anchors, energy dissipating devices, and boulder. The models for the structural elements (ring net, energy dissipating devices) are calibrated individually from quasi-static tensile tests results. The barrier model is then created assembling the structural elements, before being impacted. The tests consist in a impacting in its center a 3-module barrier, first, to one high kinetic energy impact and, second, to three consecutive impacts with a lower kinetic energy. The models results are confronted to measurements made during the experiments, considering a large set of parameters. Both models reveal satisfactory in predicting the structure response, on quantitative and qualitative points of view, and considering the boulder displacement, forces in the main cables and forces acting within the various energy dissipating devices. The quality of the prediction by each model compared to the other depends on the considered parameter. Little deviations from the experimental results are attributed to the model calibration procedure and to slight differences between the real structure and the modeled ones. In the end, the DEM approach appears suitable for modelling flexible barriers in complex loading conditions (high velocity and successive impacts).

A discrete element modelling approach for fatigue damage growth in cemented materials

This study proposes a modelling approach capable of capturing both the fatigue response and localisation of failure in cemented materials. This modelling approach takes advantage of Discrete Element Method (DEM) to reproduce the heterogeneous microstructure and crack development in cemented materials. In conjunction with this, a new constitutive model is developed to characterise the fatigue behaviour of the materials at the grain scale. The model formulation is based on coupling damage mechanics and plasticity theory and combining with a fatigue damage evolution law to describe the degrading response of cemented materials subjected to cyclic loading. The proposed model is employed to govern the explicit behaviours of DEM bonding contacts representing cement bridges between aggregates in the physical materials. The macro-behaviour is then obtained in DEM simulations as the collective response of all contacts and particles in the material domain. Through numerical experiments, the proposed modelling approach is shown to capture well the fatigue behaviour and cracking process in cemented materials subjected to cyclic loading. The microstructural effects on the fatigue response of the materials are naturally reproduced in simulations thanks to the discrete nature of DEM. These results demonstrate the capability of the proposed modelling approach as well as its potential to be a faithfully numerical technique for modelling and investigating fatigue damage in cemented materials.

Effects of technological parameters on permeability estimation of partially saturated cement paste by a DEM approach

In this study, a numerical approach developed in our group is used to assess the permeability of partially saturated cement paste based on a discrete element modelling (DEM) technique. The relationship between saturation degree and permeability is found to be in good agreement with experimental observations. Also, outcomes of a systematic study of the effects of technological parameters (i.e., hydration period, water/cement ratio and cement particle size range) on the permeability of partially saturated specimens follow expected trends. Moreover, permeability is found to be correlated to effective porosity. This is a sound basis for investigating the impact of the interfacial transition zone on water and gas permeability. Effects of partial saturation are demonstrated different for water and gas transport. Possible mechanisms underlying these permeability characteristics are discussed in this paper.