Modelling hard rock pillars using a Synthetic Rock Mass approach

Rock pillar strength and the characterisation of pillar failure mechanisms are of major importance in mine design. The recently developed Synthetic Rock Mass (SRM) approach provides a state-of-the-art numerical technique to more accurately characterize the mechanical properties of rock pillars. The SRM approach used in this thesis is based on a combination of two well accepted numerical methods, a Particle Flow Code (PFC3D) incorporating a Discrete Fracture Network (DFN). This research presents the results of a systematic study of the use of SRM modelling for hard rock pillars. The effect of assumed joint set characteristics (orientation and persistence) is first investigated through comparison of the numerical results from a series of conceptual pillar models. The joint set properties are shown to have important controls on the pillar peak strength, deformation modulus, lateral stiffness and the pillar strain-softening gradient in the post-peak stage. The effect of pillar confinement is then examined using two conceptual pillar models with varied slenderness (Width/Height ratio). The pillar confinement effect is investigated by comparing the axial and lateral stresses at the pillar core and pillar boundaries, and this effect attributed to the lateral restraint due to the loading platens. The confinement effect is further examined using a series of triaxial compression test simulations in which the pillar peak strength, residual strength and post-peak strain-softening gradient are quantified. Simulations of the development of 3D cracks in two jointed pillar models, including wing cracks, large scale crack coalescence and step path failure are presented. A 3D visualisation of internal pillar failure mechanisms is illustrated by examining crack development and the changes in the localised stresses within the pillar model. Research presented will contribute significantly to the development of a more robust SRM approach for rock pillar design.