Photogrammetric calculation of JRC for rock slope support design

For mining and civil engineering projects rock slope stability is an essential part of safety and financial considerations. While large-scale stability can be simulated using rock mass properties, at smaller scale local variations in rock properties become significant and failure purely along discontinuities is possible. Plane failures, wedging and rockfall are common occurrences at this scale. These are often prevented by bolting or shotcrete support. For temporary slopes such support measures can be costly, and an ability to simulate possible failures along discontinuity planes becomes useful for evaluation of support necessity. Conventional methods for evaluating rock mass properties require making assumptions for scale effect in upscaling for an effective slope scale. The scale effect is generally considered to be negative, while some studies show positive or no scale effect. Deriving parameters to elaborately represent mechanical properties of rock mass in a scale of a mining project would require conducting a large scale in-situ test. Representativeness of one test for a large region of interest is questionable. Photogrammetric recording of rock joint surfaces aims to automate the obtaining of rock joint roughness without the need for manual sampling and costly laboratory experiments. Measurements carried out manually using a profilometer are compared to results obtained with photogrammetry without human interaction. The results are compared to tilt table tests to obtain a ratio between the natural roughness to profiled roughness. This ratio may be interpreted as a measure of how well the joint surfaces match. The photogrammetric JRC values may be used to predict the strength of rock joints under low stress conditions, where dilatation is not prevented. Finally discussion is given concerning the applicability of the method and the need for future research.