Hybrid Finite-Discrete Element Modelling of Various Rock Fracture Modes during Three Conventional Bending Tests

The numerical techniques for modelling the rock fracture have been briefly reviewed. A hybrid finite-discrete element method (HFDEM) is proposed to simulate various fracture types of rock. A fracture model is implemented in the HFDEM for simulation of the three main fracture types. In addition, the influence of the strain rate is considered during the HFDEM modelling rock behavior. Then, two typical rock mechanism tests are employed to calibrate the HFDEM. The proposed method has well modelled the rock fracture processes and can obtain reasonable stress distribution and force–displacement curves. After that, the HFDEM is used to model three convention bending tests. The obtained rock fracture processes indicates that the HFDEM can simulate various fracture types. The obtained rock strengths and fracture toughness indicate that the HFDEM can reflect the influence of the strain rate. It is concluded that the HFDEM can model the entire and complete rock fracture process during the three convention bending tests, and it also can capture the rock’s behavior on the strain rate.

On the efficiency of coupled discrete-continuum modelling analyses of cemented materials

Computational load of discrete element modelling (DEM) simulations is known to increase with the number of particles. To improve the computational efficiency hybrid methods using continuous elements in the far-field, have been developed to decrease the number of discrete particles required for the model. In the present work, the performance of using such coupling methods is investigated. In particular, the coupled wall method, known as the “wall-zone” method when coupling DEM and the continuum Finite Differences Method (FDM) using the Itasca commercial codes PFC and FLAC respectively, is here analysed. To determine the accuracy and the efficiency of such a coupling approach, 3-point bending tests of cemented materials are simulated numerically. To validate the coupling accuracy first the elastic response of the beam is considered. The advantage of employing such a coupling method is then investigated by loading the beam until failure. Finally, comparing the results between DEM, DEM-FDM coupled and FDM models, the advantages and disadvantages of each method are outlined.

Analysis of the Quasi-Static and Dynamic Fracture of the Silica Refractory Using the Mesoscale Discrete Element Modelling

Computer modelling is a key tool in the optimisation and development of ceramic refractories utilised as insulation in high-temperature industrial furnaces and reactors. The paper is devoted to the mesoscale computer modelling of silica refractories using the method of homogeneously deformable discrete elements. Approaches to determine the local mechanical properties of the constituents from the global experimental failure parameters and respective crack trajectories are considered. Simulations of the uniaxial compressive and tensile failure in a wide range of quasi-static and dynamic loading rates (102 s−1) are performed. The upper limit of the dynamic loading rates corresponds to the most severe loading rates during the scrap loading on the refractory lining. The dependence of the strength, fracture energy, and brittleness at failure on the loading rate is analysed. The model illustrates that an increase in the loading rate is accompanied by a significant change in the mechanical response of the refractory, including a decrease in the brittleness at failure, a more dispersed failure process, and a higher fraction of the large grain failure. The variation of the grain–matrix interface’s strength has a higher impact on the static compressive than on the static tensile properties of the material, while the material’s dynamic tensile properties are more sensitive to the interface strength than the dynamic compressive properties.

Evidence of a Unique Critical Fabric Surface for Granular Soils

The critical state of granular soils needs to make proper reference to the fabric that develops at critical state. This study substantializes the concept of critical fabric surface (CFS) which attracts the fabric state of granular soils upon continuous shearing. Numerical experiments using discrete element modelling (DEM) are conducted under drained and undrained conditions with varies Lode angles. Fabric tensors are defined based on the normals of all contacts and of the strong force contacts only. Both tensors have their spherical component preserved such that the information of coordination number can be carried. A separate series of low confining pressure undrained test are conducted to probe the fabric states of soils in the post-liquefaction regime. Finally, a single CFS spanning across a wide range of coordination numbers is established based on the DEM results. The CFS concept provides an important reference state for soils sheared to large strains in complementary to the traditionally defined critical state. It provides a new perspective to interpret and model the mechanics of granular soils in both pre- and post- liquefied regimes. The evolution of fabric shows that the normalized strong-contact fabric evolves linearly with the stress ratio even for liquefied or anisotropically consolidated soils.

Discrete Element Modelling of Sedimentation and Tectonics: Implications for the Growth of Thrust Faults and Thrust Wedges in Space and Time, and the Interpretation of Syn-Tectonic (Growth) Strata

Thrust faults, and thrust wedges, are an important part of the surface morphology and structure of many contractional mountain belts. Analogue models of thrust wedges typically provide a map- and/or side-view of their evolution but give limited insight into their dynamic development. Numerical modelling studies, both kinematic and mechanical, have produced much insight into the various controls on thrust wedge development and fault propagation. However, in many studies, syn-tectonic sediments or “growth strata” have been modelled solely as passive markers and thus have no effect on, or do not feedback into, the evolving system. To address these issues, we present a high-resolution, 2D, discrete element model of thrust fault and wedge formation and the influence that coeval sedimentation may have on their evolution. We use frictional-cohesive assemblies, with flexural-slip between pre-defined layers, to represent probable cover rheologies. The syn-tectonic strata added during contraction are frictional-cohesive and we can think of them as “mechanical growth strata” as they interact with, and influence, the growing thrust wedge. In experiments of thrust wedge development without syn-tectonic sedimentation, a forward-breaking sequence is seen: producing a typical thrust-wedge geometry, consistent with analogue and numerical models. In general, the inclusion of syn-tectonic sedimentation produces thrust wedges composed of fewer major forward-vergent thrusts and with only minor thrust activity in the foreland. In most of these models the sequence of thrust activity is complex and not simply forward-breaking. With increasing sedimentation, the frontal thrust has much greater displacement and overrides a much thicker package of earlier syn-tectonic sediments. Very high syn-tectonic sedimentation results in the formation of a single basin-bounding thrust fault and no thrust-wedge per se. At the local (outcrop) scale of individual fault-related folds, high syn-tectonic sedimentation alters fault-fold evolution by producing steeper ramps, whereas low syn-tectonic sedimentation allows shallower ramps that may flatten and propagate into the syn-tectonic strata. Implications of these results for the interpretation of thrust faults and wedges and their interaction with associated growth strata are discussed.

Use of Discrete Element Modelling to Evaluate the Parameters of the Sampling Theory in the Feed Grade Sampler of a Sulphide Gold Plant

Cross-stream cutters are widely used in the mining and resources industry to obtain representative samples of particulate flows. Discrete element modelling (DEM) and analysis can be used to investigate influences of operational parameters, sampler design and material physical properties in the generation of the Increment Extraction Error (IEE), which when present, results in a frequently biased, non-representative sample. The study investigates the practicality of the rules and recommendations proposed by Dr. Pierre Gy that were developed and established as principles for the correct extraction of samples in industrial sampling equipment. Results validate Pierre Gy’s sampling theory using DEM in a cross-stream cutter of a sulphide gold plant. Importantly, the outcomes indicate that careful consideration must be given to physical ore properties and, consequently, that sampling systems should be developed specifically to each application.