IV International Workshop on Modern Trends in Geomechanics
G. Viggiani, D. Salciarini, F. Silvestri, C. Tamagnini, G.M.B. Viggiani (Eds)Assisi, May 16--19, 2016

DEM MODELLING OF COHESIVE AND CEMENTITIOUS MATERIALS – MODEL
CONCEPTUALISATION, CALIBRATION AND VALIDATION
J. Y. Ooi, A. Janda and J. P. Morrissey
School of Engineering
The University of Edinburgh, United Kingdome-mail: j.ooi@ed.ac.uk

Keywords: discrete element method, DEM, particle scale modelling, mesoscale modelling, cohesive solid,
cementitious material, unconfined strength, calibration, upscaling.
Summary. The discrete element method (DEM) has been increasingly used to study granular materials. This paper
describes the use of DEM to study the behaviour of cohesive and cementitious materials. We propose a mesoscopic
scale approach whereby a visco-elasto-plastic frictional adhesive contact model was developed to represent a cohesive
granular material such as clay and an inter-particle bonded contact model was developed to represent a cementitious
granular material such as rock or concrete.

1 INTRODUCTION TO THE MESOSCOPIC COHESIVE AND BONDED DEM MODELSCohesive and cementitious granular materials are common in nature, such as soils and rock, and also in manyindustries including chemical, food, pharmaceutical, construction and mining. Computer simulation using the Discrete
Element Method (DEM) is a powerful tool to study and provide new insights into the behaviour of these materials.
However, the success of this approach is dependent on the capabilities of the simulations to reproduce the real
behaviour of the material. In this paper, we present an investigation using a mesoscopic scale modelling of cohesiveand cementitious materials by means of the Discrete Element Method.
A visco-elasto-plastic frictional adhesive contact model was developed recently at the University of Edinburgh andused to reproduce the key mechanical behaviour of a cohesive granular material [1-4]. The contact model reflects thephysical phenomena of adhesive contact forces in fine cohesive particles and accounts for both elastic and plastic
contact deformation with the adhesion being dependent on contact plasticity.
For cementitious granular materials, one chief advantage of DEM over continuum based techniques is that it does
not make assumptions about how cracking and fragmentation initiate and propagate since a DEM system is naturally
discontinuous. An inter-particle bonded DEM contact model based on the Timoshenko beam theory which considers
axial, shear and bending behaviour of the bond was developed to produce a realistic representation of a cemented
granular material [5].

J. Y. Ooi, A. Janda and J. P. Morrissey
2. MODEL SCALING, CALIBRATION AND VALIDATIONThe suitability of the viso-elasto plastic adhesive contact model was investigated by simulating different bulk testsof cone penetration, confined compression and unconfined loading to failure of a cohesive material. Furthermore, thescaling laws of the contact model parameters to produce the same load-deformation behaviour invariant of the particle
size used in the simulations were further investigated [3,4]. Besides, a scientific calibration methodology for thecontact model parameters was developed based on relatively simply bulk experiments. The results show that the DEM
contact model is capable of reproducing the macroscopic mechanical behaviour of cohesive materials including thecharacteristic stress history dependent strength observed in real cohesive solids. Moreover, the developed calibration
methodology for the contact model parameters was validated against bulk test experiments showing good quantitative
predictions of the unconfined strength of the material. Finally, the behaviour of the cohesive material in a large scale
application involving blade cutting was investigated. In this case, upscaling of particles size following the scaling laws
found for the contact model parameters were applied in order to reduce the computational time of the simulations. The
study demonstrates a successful application of DEM simulation of a large scale application of a cohesive granularprocess using a DEM model with appropriate scaling laws and material characterization experiments.
The bond model was first verified by simulating both the bending and dynamic response of a simply supported
beam. The loading response of a concrete cylinder was then investigated and compared with the Eurocode equation
prediction. The results show significant potential for the new model to produce satisfactory predictions for
cementitious materials. A unique feature of this model is that it can also be used to accurately represent many
deformable structures such as frames and shells, so that both particles and structures or deformable boundaries can be
described in the same DEM framework
3. ACKNOWLEDGEMENTS
The DEM models were developed in collaboration with N. Brown, S. Thakur, J.F. Chen and J. Sun. The support
from the EU Marie Curie Initial Training Network (Grant No. 235877 and No. 607453), EPSRC and DEM Solutions
Ltd are gratefully acknowledged.
REFERENCES[1] S. Thakur, J. Morrissey, J. Sun, J. Chen, J. Ooi, “Micromechanical analysis of cohesive granular materials using
the discrete element method with an adhesive elasto-plastic contact model”, Granular Matter 16 (2014), 383 – 400[2] S. Thakur, H. Ahmadian, J. Sun, J. Ooi, “An experimental and numerical study of packing, compression, andcaking behaviour of detergent powders”, Particuology 12 (2014), 2–12.
[3] A. Janda and J.Y. Ooi, “DEM modelling of cone penetration and unconfined compression in cohesive solids”
Powder Technology, (2015).
[4] S. Thakur, J.Y. Ooi and H. Ahmadian, “Scaling of discrete element model parameters for cohesionless andcohesive solid”, Powder Technology, (2015).
[5] N. J. Brown, J.-F. Chen and J.Y. Ooi, “A bond model for DEM simulations of cementitious materials anddeformable structures”, Granular Matter 16 (2014), 299–311.