| A flow-coupled Discrete Element Model for 2-D granular assembly of discs has been developed to address the class of flow coupled problems in granular media. Grains are represented by circular discs; to simulate flow, a geometrically coupled channel network is created by assigning nodes to pores, and flow channels to pore throats. Flow rates in channels are assumed to be proportional to the pressure gradient according to Hagen-Poiseuille equation. The model assumes a single-phase fluid flow under steady-state conditions.;Hydraulically induced fracture in an assembly of cohesionless discs has been successfully simulated using the flow coupled DEM, HYDROFRAC. Model describes a progressive development of a single large flow channel with parting of the system. Based on micromechanical principles an equation for fracture initiation pressure has been derived which gives reasonable estimates of fracture initiation pressures in idealized assembly of discs, which further validates the approach developed. The model is a pure departure from the continuum mechanics approach and clearly tackle anisotropy and heterogeneity issues from a more fundamental approach.;The effect of confining pressure, density, stress ratio, and permeability of the medium on fracture initiation pressures are investigated. The fundamental mechanisms of fracture initiation and propagation at grain scale levels are hypothesized. The parting and wedging action by the pore fluid are found to be the main driving mechanisms for fracture initiation. It is established that the density, homogeinity, and the anisotropic fabric control fracture initiation pressures along with stress states. The annular dilation, non-linear behaviour around the borehole and borehole breakouts have been reasonably simulated. It is clear from the simulations that the DEM have great power in emulating realistic behaviour of deformations in granular materials. Possible application and future extensions of the model are discussed.;Comparisons with analytical solutions for simple systems have verified the model's ability to calculate correctly the particles movement and their interactions at contacts due to applied boundary stresses and pore pressures. The pressures in the medium obtained by solving a network flow problem corresponds precisely to the pressure distributions of 2-D analytical solutions using Darcy's law. |
