Two-dimensional discrete element simulations of the fracture behaviour of slate

The fracture behaviour of slate, which is a transversely isotropic rock with a (extreme) large strength anisotropy, is investigated. Two-dimensional discrete element simulations are conducted, and compared to earlier laboratory experiments of uniaxial loading of rectangular samples and diametrical loading of disks. The observed fracture patterns in the experiments, as well as in the simulations, are a complex combination of fractures in the schistosity direction and/or in other directions. A conceptual model is put forward, whereby the strength anisotropy on the element scale is related to the strength anisotropy on the sample scale and to the deformation behaviour. It is observed that the load configuration (i.e. load direction relative to the schistosity layers) determines whether fractures grow in the layer direction only, or in both layer and non-layer directions. Moreover, the transition of failure mode (shear or tensile) as a function of the load configuration is captured. Finally, the non-linear behaviour on sample scale is explained by micro-fracturing in the schistosity direction as a means of dissipating energy.

► Fracture behaviour of highly anisotropic slate rock is studied by 2D numerical simulations and experiments. ► Fractures occur in schistosity direction and/or other directions. ► Load configuration relative to schistosity determines fracture directions and failure modes. ► Strength anisotropy on different scales is linked, and related to deformation behaviour. ► Energy dissipation through schistosity micro-fracturing translates in non-linear deformation behaviour.