Measuring physical aperture of a fracture affected by dislocation using photogrammetry

Accurate physical aperture measurement is essential for modeling fluid flow through fractures. Stress changes, such as normal and shear stresses, can alter physical aperture, affecting flow, especially near nuclear waste sites where radionuclides may enter groundwater through fracture networks. Understanding flow under different stress conditions is key to evaluating underground excavation safety. This study focuses on accurately determining physical aperture in fractures impacted by dislocation.
A 6 cm × 6 cm × 10 cm Kuru gray granite sample with a tensile fracture was studied under dislocation. Markers with predefined distances were applied to align and scale dislocated fracture surfaces using photogrammetry. At each dislocation step, photogrammetry captured surface positions to calculate physical aperture. A local coordinate system was established for the bottom half of the sample, enabling precise measurements of the relative positions of the top and bottom surfaces with and without dislocation. The Root Mean Square Error (RMSE) of the photogrammetric measurements was approximately 35 μm. Ceramic calibration blocks were used as ground truth to assess the accuracy of the photogrammetric method. The physical aperture showed a nonlinear relationship with displacement.
This photogrammetric approach provides a deeper understanding of how dislocations change physical apertures, which can consequently affect both fluid flow behavior and shear strength. It also demonstrates the potential of photogrammetry for accurately determining physical aperture during shear tests.