Now showing 1 - 2 of 2
  • Publication
    Localisation of normal faults in multilayer sequences
    Existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong, and brittle, layers and are later linked in weak, and ductile, layers. We use the Discrete Element Method (DEM) for modelling the growth of a normal fault in a brittle/ductile multilayer sequence. The modelling reveals that faults in brittle/ductile sequences at low confining pressure and high strength contrast localise first as Mode I fractures in the brittle layers. Low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers. The initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers. Faults localise, therefore, as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults. The modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared to weak layers, where the difference in propagation distance is most likely related to strength and/or ductility contrast. Layer dependent variations in fault propagation rates generate fringed rather than smooth fault tip lines in multilayers.
    Scopus© Citations 135  890
  • Publication
    The impact of porosity and crack density on the elasticity, strength and friction of cohesive granular materials : insights from DEM modelling
    Empirical rock properties and continuum mechanics provide a basis for defining relationships between a variety of mechanical properties, such as strength, friction angle, Young’s modulus, Poisson’s ratio, on the one hand and both porosity and crack density, on the other. This study uses the Discrete Element Method (DEM), in which rock is represented by bonded, spherical particles, to investigate the dependence of elasticity, strength and friction angle on porosity and crack density. A series of confined triaxial extension and compression tests was performed on samples that were generated with different particle packing methods, characterised by differing particle size distributions and porosities, and with different proportions of pre-existing cracks, or uncemented grain contacts, modelled as non-bonded contacts. The 3D DEM model results demonstrate that the friction angle decreases (almost) linearly with increasing porosity and is independent of particle size distribution. Young’s modulus, strength and the ratio of unconfined compressive strength to tensile strength (UCS/T) also decrease with increasing porosity, whereas Poisson’s ratio is (almost) porosity independent. The pre-eminent control on UCS/T is however the proportion of bonded contacts, suggesting that UCS/T increases with increasing crack density. Young’s modulus and strength decrease, while Poisson’s ratio increases with increasing crack density. The modelling results replicate a wide range of empirical relationships observed in rocks and underpin improved methods for the calibration of DEM model materials.
    Scopus© Citations 242  2031