Abstract

Bonded-particle modelling is a powerful approach for simulating particle made structures with enhanced abilities, i.e., structures that are able to deform, brake/fracture, and thus interact with other particles of a DEM simulation in an enhanced complex manner. This modelling approach is based on connecting particles with beam elements (commonly termed bondings, with each bonding connecting two particles) to create a bonded-particle model (BPM), typically consisting of a large number of particles and bondings. The behaviour of such a BPM can be adjusted in two categories: via properties related to the particles, e.g. their mass, shape, or frictional characteristics, and via properties related to the bondings, e.g. their Young’s moduli or breakage criteria. This contribution presents developments in complex bonded-particle modelling for achieving flexible/deformable and breakable/fracturable structures and highlights the enhanced capabilities made possible by using this approach. For this purpose, various applications for bonded-particle modelling in DEM simulations are presented, with selected case studies each demonstrating the effectiveness of bonded-particle modelling in solving practical engineering problems, including: - 1D BPMs, e.g., deformable beams or ropes and chains, - 2D BPMs, e.g., membranes, textiles, nets, bags, shell-like parts (e.g. silos), or conveyor belts (with particular reference to dynamic belt simulation), and - 3D BPMs, e.g., complex-breakable structures (e.g. with considering crack formation or dynamic impact handling; e.g. illustrated on filter cake material). Furthermore, possible interaction scenarios, including interactions of BPMs to particles, rigid parts, other BPMs, or even in terms of SPH (Smoothed-Particle Hydrodynamic) or MBD (Multibody Dynamics), are addressed. Finally, current developments and potential future directions in this field are outlined, and potentials for extending this modelling approach to further application areas are discussed.

Abstract

Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute for Radiological protection and Nuclear Safety (IRSN, France) due to their expected gap-filling capacity in engineered barrier systems for the geological disposal of radioactive waste. In the short term, after installation, the hydro-mechanical behaviour of these pellet-based structures is governed by pellet-pellet interactions, which have been characterised experimentally by oedometer compression tests and numerically by discreteelement modelling of single-layered pellet skeleton samples. In this work, we integrate these experimental and numerical tools to characterise the compressibility of three-layered pellet-based structures with axis-oriented arrangements. We validate the simulated deformation of bentonite pellet samples against experimental data and analyse the evolution of the dry density distribution and axial stiffness along the oedometer compression curve. Our integrated approach has implications for the emplacement and monitoring in situ tests on multi-layered pellet-based barrier systems.

Abstract

Laboratory-scale cone penetration tests are often carried out to calibrate the response of cone penetration, and in particular cone tip resistance to soil characteristics. However, because of the limited sample size, sample boundaries can often affect the measured cone resistance in laboratory tests. This paper presents numerical simulations using the discrete element method (DEM) to study the effect of boundary condition on cone penetration calibration chamber tests. Numerical simulations were performed under flexible (BC1) and laterally-constrained (BC3) boundary conditions on K0consolidated models at different relative densities and vertical stresses. Additional models were simulated with periodic boundaries (BC5) to model the free-field condition. To track the radial stress variations in different sections of the chamber, scattered representative volume elements (RVE) were embedded in the models. Particle displacements and contact force chains were examined to determine the relation between microscopic variables and macroscopic response of the specimens subjected to cone penetration under different boundary conditions. Larger cone resistances were obtained under BC3 condition than those in BC1 condition. For the chamber-to-cone diameter ratio of 25 adopted in this study, the influence of the lateral boundary was found to be negligible in loose to medium-dense assemblies, while the effect of chamber boundary amplified in dense to very dense samples with increasing relative density and reduced with increasing vertical stress. This was attributed to the higher radial stress induced along the cone penetration path in laterally-constraint BC3 models. Based on these findings, a correction factor is proposed to better estimate free-field penetration resistance from calibration chamber experiments.