An Alternative Approach for Semi-Automatic Delineation of Rock Blocks on 3D Meshes and Engineering Application


Regine Tsui
Aurecon Hong Kong Limited, Hong Kong
Jonathan Hart
Aurecon Hong Kong Limited, Hong Kong
Wenzhu Hou
GeoRisk Solutions Limited, Hong Kong
Alan Ng
GeoRisk Solutions Limited, Hong Kong


Auto-identification of rock blocks on 3D models is a useful new tool for rock engineering. It has the potential, when undertaken with rock engineering professionals, to delineate remotely, potentially unstable rock blocks associated with adverse discontinuities. An alternative approach is proposed to semi-automatically delineate rock blocks on 3D meshes, which does not require prior extraction and fitting of discontinuity planes. The proposed approach starts with trace extraction, exploiting the fact that the contact between two rock blocks is most often manifested by a trace (i.e., an exposed line) on the rock surface. Geometrically, the trace is usually either a concave edge or a depressed line. These traces are first extracted due to their higher concavity or darkness compared to their neighbouring mesh faces. After post-processing, the mesh is segmented into sub-meshes around the extracted trace lines. The algorithms are implemented in Python and are tested on three rock slopes, including: (1) a rock slope in Ouray, USA; (2) a natural rock outcrop in Ma Shi Chau, Hong Kong; and (3) a rock slope in a former quarry currently being redeveloped as part of a large-scale site development in Hong Kong. Our approach can enrich the rock mapping results and help identify critical rock blocks which may be at risk of planar failure.

September 17, 2022
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