Characterization of the effect of normal load on the discontinuity morphology in direct shear specimens using X-ray micro-CT

Discontinuities in brittle geomaterials, including concrete and rock, represent localized zones of weakness and enhanced hydraulic transmissivity that often control the hydromechanical behavior of the medium. The shearing of discontinuities and the resulting morphological changes can significantly alter this behavior. In this work, a procedure is developed to characterize sheared discontinuity replicas as a function of the applied normal load using X-ray micro-computed tomography (micro-CT) imagery. A specimen design and testing procedure that facilitates CT scanning is presented along with an image processing procedure to quantify the morphological changes in the specimens. Subsequently, the results of direct shear testing and image-based measurements of mean fracture aperture, surface area, median effective aperture, and the preferential orientation of fracture void space are presented and discussed. Application of the procedure developed herein yields characteristics of the morphology of sheared discontinuities that were previously not possible to obtain or that were time consuming to collect with destructive sectioning methods.