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• We study the effect of aperture variability on incipient karst genesis in fractured limestones. • The sensitivity of karstification to aperture heterogeneity is affected by fracture network hierarchy. • Aperture variability may alter the dynamics and structure of dissolution development. We conduct numerical simulations to investigate the role of aperture heterogeneity in early-stage karstification of a fractured carbonate rock. The fracture network is formed by a dominant set of persistent fractures and a secondary set of short fractures that abuts the dominant set. The variable aperture distribution priori to dissolution is derived from geomechanical simulation. We report that the extent to which aperture distribution affects karstification is jointly controlled by the far-field stress orientation, flow direction and structural hierarchy. When reactive flow occurs in the direction of the dominant fracture set, karst conduits only develop locally along a few large discontinuities preferentially oriented for frictional sliding, such that differential stress can produce shear dilatancy and enhance hydraulic transmissivity. In contrast, when reactive flow is along the direction of the secondary fracture set, the far-field stress loading has a negligible impact on the emergent dissolution pattern except somewhat impact on the onset time of breakthrough. In this case, the developed conduits exhibit much more tortuous pathways associated with numerous branches. Our results demonstrate that flow heterogeneity induced by geometrical complexities and geological conditions seems to play an essential role in the karst growth in fractured rocks. The research findings provide useful insights into the interplay among tectonic structures, in-situ stresses and karst cavities, which have important implications for underground engineering activities in karstified fractured rocks. [ABSTRACT FROM AUTHOR]

We develop a new numerical model that couples hydraulic, mechanical and chemical processes to investigate the dynamic influence of stress on incipient karst formation in natural fracture networks. Our geological models are constructed based on realistic fracture patterns mapped from outcrops, which capture a wide range of spatial distribution and organization of carbonate fracture networks. We simulate the dissolutional growth of karst conduits in the fractured formation under varied initial aperture distribution and in-situ stress loading. We found that the impact of the stress effect on karstification depends on the relative relationship between the flow direction and the structural anisotropy of the fracture network. When the flow occurs in the direction corresponding to the most continuous fracture network structures, karst conduits only develop locally along a few long fractures with an orientation favorable to frictional sliding under the differential stress. Indeed, the important shear-induced dilation of these fractures generates a higher aperture and thus hydraulic conductivity. In contrast, when flow is in the direction transverse to the most continuous fractures, the far-field stress loading has a negligible impact on the emergent dissolution pattern but a perceptible impact on the onset time of breakthrough. In this later case, the developed conduits are much more tortuous with many branches. In both cases, the presence of initial aperture variability facilitates the development of a uniform dissolution front and therefore delays breakthrough. Our results demonstrate that the heterogeneity induced by geometrical complexities, enhanced by in-situ stress conditions, may play a decisive role on the karstification processes in fractured rocks. The results from this research provide important insights into the spatial relationship between tectonic structures, geomechanical constraints and karstogenesis. [ABSTRACT FROM AUTHOR]