Evaluation of Digital Rock Mass Discontinuity Mapping Techniques for Applications in Tunnels

High-quality coloured 3D point clouds can now be readily generated by digital surveying techniques such as structure from motion (SfM) photogrammetry and terrestrial laser scanning (TLS). Point clouds allow discontinuities to be mapped digitally on rock slopes and this has been widely studied in Hong Kong. In comparison, few similar applications have been reported in tunnels in Hong Kong. To extend the application of this technology for tunnel excavation, we carried out three site trials in two drill-and-blast hard rock tunnels in Hong Kong. Both SfM photogrammetry and TLS were used to generate point clouds for the exposed rock tunnel surfaces. The generated point clouds were then tested for semi-automatic extraction of rock mass discontinuities using DRM2.0, Aurecon’s in-house developed software. This paper provides detail accounts of data acquisition, data processing, present the findings on the performance of semi-automatic identification of discontinuities, and the comparison between SfM and TLS techniques. The paper also discusses the challenges in digital mapping inside tunnels and provide useful suggestions on conducting laser scanning and photogrammetry in tunnels.