Cardona, A., Finkbeiner, T., & Santamarina, J. C. (2021). Natural Rock Fractures: From Aperture to Fluid Flow. Rock Mechanics and Rock Engineering.
Fractures provide preferential flow paths and establish the internal “plumbing” of the rock mass. Fracture surface roughness
and the matedness between surfaces combine to delineate the fracture geometric aperture. New and published measurements
show the inherent relation between roughness wavelength and amplitude. In fact, data cluster along a power trend consistent
with fractal topography. Synthetic fractal surfaces created using this power law, kinematic constraints and contact mechanics are used to explore the evolution of aperture size distribution during normal loading and shear displacement. Results
show that increments in normal stress shift the Gaussian aperture size distribution toward smaller apertures. On the other
hand, shear displacements do not affect the aperture size distribution of unmated fractures; however, the aperture mean and
standard deviation increase with shear displacement in initially mated fractures. We demonstrate that the cubic law is locally
valid when fracture roughness follows the observed power law and allows for efficient numerical analyses of transmissivity.
Simulations show that flow trajectories redistribute and flow channeling becomes more pronounced with increasing normal
stress. Shear displacement induces early aperture anisotropy in initially mated fractures as contact points detach transversely
to the shear direction; however, anisotropy decreases as fractures become unmated after large shear displacements. Radial
transmissivity measurements obtained using a torsional ring shear device and data gathered from the literature support the
development of robust phenomenological models that satisfy asymptotic trends. A power function accurately captures the
evolution of transmissivity with normal stress, while a logistic function represents changes with shear displacement. A complementary hydro-chemo-mechanical study shows that positive feedback during reactive fluid flow heightens channeling.