Critical stress localization of flow associated with deformation of well-fractured rock masses, with implications for mineral deposits

Abstract

Abstract Fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods (UDEC) which couple mechanical and hydraulic behaviour. A series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state. Slip on parts of the fracture network causes the opening up of some fractures, often at fracture intersections. Thus, a change in the stress state results in a sudden localization of deformation and fluid flow. A series of plots of hydraulic conductivity v. differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow. The onset of localized deformation and fluid flow is a critical point phenomenon, resulting in fractal properties. Fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum-based description of the flow. The significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems.