Finite Element-based Digital Image Correlation (FE-DIC) procedures are developed to determine full-field displacements, specifically for the analysis of discontinuous rock samples. This study evaluates the mechanical behavior of grouted discontinuities in geomaterials, capturing the effects of joint morphology, grouting material, and loading conditions through the FE-DIC approach. Artificial joints were introduced in sandstone, basalt, and concrete specimens with inclinations of 30 \(^\circ\) and 45 \(^\circ\) , and grouted using epoxy resin, cement mortar, and polyvinyl acetate. The specimens were subjected to uniaxial loading to induce Variable Normal Load (VNL) conditions across the joints, and the full-field displacement data were captured using FE-DIC alongside conventional LVDT and UTM measurements. The FE-DIC technique facilitated the quantitative extraction of mechanical parameters such as normal and shear stiffness, enabling its use as a characterization tool rather than solely a deformation measurement method. For rough joints, a Richards’ three-parameter logistic model was fitted to capture the non-linear stress-displacement behaviour, and a new parameter, the specific energy of the joint, was introduced to quantify mechanical energy utilized per unit area for the movement of the joint surface. The spatial distribution of this parameter along the joint length revealed the influence of grouting materials and demonstrated how the proximity of a circular cavity alters the joint’s shearing behaviour. The study also compared Variable Normal Load (VNL) tests with conventional Constant Normal Load (CNL) direct shear tests, showing that shear stiffness under VNL conditions is significantly higher due to load-path dependency. Overall, the work demonstrates the efficacy of FE-DIC as a visualization tool and a rigorous method for the quantitative characterization of jointed geomaterials.
