Time-dependent DEM based fracture simulations at the grain size level for brittle heterogeneous solids

Adiscrete element numerical model forLac du Bonnet graniteis built for time-dependent fracture simulations. The heterogeneity is consideredbydifferentmineral components randomly distributed inside the rock. The minerals are representedby elastic Voronoi cellsconnected by elasto-plastic contacts. The Hillig-Charles equationis implanted in thenumericalmodel for analyzingtime-dependent damage due tosubcritical crack growth. The damageprocesses duringuniaxial compressive creep tests are investigated. The numericalsimulations reveal not only reasonable lifetime of the specimens under different loads, but also show primary, secondary and tertiary creepstagesuntil final failure characterized by macroscopic fracturing.The simulationresultsof crack growth and damage index evolution deliver adeeperinsight into the microscopic damage process

A Coupled DEM-CFD Simulation of Rip-Rap Revetments in Tidal Areas

River, Estuarine and Coastal Dynamic

Voronoi-Based discrete element analyses to assess the influence of the grain size and its uniformity on the apparent fracture toughness of notched rock specimens

The fracture toughness reflects the rock resistance to crack propagation, and therefore represents an important parameter for rock fracture assessments. From a strict point of view, the real fracture toughness ( KIC ) corresponds to a cracked situation in which the notch radius is theoretically equal to zero. However, most of the defects in rocks have a finite radius and, therefore, should be studied as notch-type defects. Here, the notch effect is numerically studied together with the influence of the grain size and the sorting coefficient (grain size uniformity) on the apparent fracture toughness ( KIN ). To this end, several four-point bending tests with different U-shaped notch radii, mean grain sizes and degrees of uniformity in grain size and shape have been simulated using the Discrete Element Method. In order to represent the grains of the rocks, the Voronoi tessellation is used to create randomly sized and distributed polygonal blocks. These Voronoi polygons have been defined, on the one hand, by an average edge length of 1, 2 and 3 mm, and, on the other hand, by a different number of iterations ( n ) in the relaxation process during the generation of the polygons, which defines the grain size uniformity. The numerical analyses performed and the interpretation of the results show a clear notch effect in all the studied cases, as the apparent fracture toughness ( KIN ) increases with notch radius. Finally, the obtained stress fields at the notch tip have been compared to those obtained from the traditional finite element method.The authors of this work would like to express their gratitude to the Spanish Ministry of Economy and Competitiveness for financing the National Plan Project (Ref. BIA2015-67479-R) under the name of “The Critical Distance in Rock Fracture”, to the Department of Universities and Research, Environment and Social Policy of the Government of Cantabria, for financing the Project “Characterization of the fracture process in rocks for geothermal applications”, and to the DAAD for the short-term research grant given to J. Justo for his research visit at TU Bergakademie Freiberg

Forschungsprojekt Gebirgsstabilität (GeoStab): Geogefahren unter regionalen Aspekten: Methodik zur integralen Bewertung der Gebirgsstabilität zur Ableitung von Geogefahren unter regionalgeologischen Aspekten

Im Projekt GeoStab wurde eine numerische Methode entwickelt zur integralen Bewertung der Gebirgsstabilität des Untergrundes auf der Grundlage regionalgeologischer 3D-Modelle. Dabei wurden natürliche Objekte – wie Störungszonen sowie Gebirgsbereiche um unterirdische Hohlräume (z.B. Altbergbau oder Tunnel) – besonders berücksichtigt. Mit der entwickelten Methode können beschrieben werden Deformationen an Diskontinuitäten, großräumige Spannungs- und Deformationsfelder des Untergrundes und der Einfluss bergbaulicher Grubenfelder auf die Stabilität des umgebenden Gebirges. Die Methode soll Behörden dazu dienen, bei Infrastrukturprojekten wie Tunnel- oder Straßenbaumaßnahmen eine geotechnisch geeignete und möglichst sichere Trassenführung zu finden. Redaktionsschluss: 06.12.202