A photogrammetric approach for quantifying the evolution of rock joint void geometry under varying contact states

Accurate measurement of the evolution of rock joint void geometry is essential for comprehending the distribution characteristics of asperities responsible for shear and seepage behaviors. However, existing techniques often require specialized equipment and skilled operators, posing practical challenges. In this study, a cost-effective photogrammetric approach is proposed. Particularly, local coordinate systems are established to facilitate the alignment and precise quantification of the relative position between two halves of a rock joint. Push/pull tests are conducted on rock joints with varying roughness levels to induce different contact states. A high-precision laser scanner serves as a benchmark for evaluating the photogrammetry method. Despite certain deviations exist, the measured evolution of void geometry is generally consistent with the qualitative findings of previous studies. The photogrammetric measurements yield comparable accuracy to laser scanning, with maximum errors of 13.2% for aperture and 14.4% for void volume. Most joint matching coefficient (JMC) measurement errors are below 20%. Larger measurement errors occur primarily in highly mismatched rock joints with JMC values below 0.2, but even in cases where measurement errors exceed 80%, the maximum JMC error is only 0.0434. Thus, the proposed photogrammetric approach holds promise for widespread application in void geometry measurements in rock joints.