This paper introduces the use of 3D Light Detection and Ranging (LiDAR) for measuring rock mass discontinuities and tunnel excavation profile details, based on a case study of the Raabstollen tunnel in eastern Styria, Austria. The basic survey procedure involves:
creating a comprehensive 3D LiDAR point cloud model (PCM);
forming detailed triangulated surface model (TSM) from the PCM; and
mapping of fracture network characteristics (discontinuity orientation, size, intersection and termination) using advanced digital processing techniques.
The result is an actual discrete fracture network being mapped directly on the excavation surface, which facilitates evaluation of over- and underbreaks and provides a permanent digital archive for further analysis and evaluation. This case study shows that LiDAR surveys can provide high quality data for both geological documentation (especially rock mass structure) and excavation geometry.
Geo-spatial data representations of rock mass conditions encountered during tunnel construction are becoming increasingly common, as they have been found to facilitate technical and economical project success. However, the immediate installation of ground support at the working face gives the engineering geologist/ tunnel engineer limited opportunity to inspect and document the ground conditions, and rock mass conditions exposed in the crown area are often not directly accessible for close inspection and measurements. The increased application of remote characterization methods has greatly enhanced tunneling documentation. Over the last 10 years, digital photogrammetry soft-ware has evolved into useful mapping tools for underground excavation (e.g. Gaich et al 1998, 2005, Birch 2008). More recently, terrestrial Light Detection and Ranging (LiDAR), also referred to as 3D terrestrial laser scanning (TLS), has seen increased application in rock mass characterization studies (e.g., Kemeny & Turner 2008, Ferre-ro et al 2009, Lato 2010, Sturzenegger 2010, Liu & Kieffer 2011).
