Geotechnical and operational applications for 3-dimensional laser scanning in drill and blast tunnels

Three-dimensional laser scanning (Lidar) techniques have been applied to a range of industries while their application to the geological environment still requires development. Lidar is a range-based imaging technique which collects a very accurate, high resolution 3-dimensional image of its surroundings. While the use of Lidar in underground environments has been primarily limited to as-built design verification in the past, there is great value in the scan data collected as the excavation advances. The advantages of employing a static Lidar system for geotechnical and operational applications have been demonstrated at a drill and blast tunnel operation at the Sandvika–Asker Railway Project near Oslo, Norway as well as in two other test tunnels in Oslo. The increased scanning rate of newer systems makes it possible to remotely obtain detailed rockmass and excavation information without costly delays or disruption of the construction workflow with a simple tripod setup. Tunnels are non-traditional environments for laser scanners and add limitations to the scanning process as well as the in-office interpretation process; these are discussed. Operational applications of the data include: calculation of shotcrete thickness, as-built bolt spacing, and regions of potential leakage. The authors find that Lidar data, when correctly interpreted, can also provide detailed 3-dimensional characterization of the rockmass. Geometrical characterization of discontinuity surfaces including location, orientation, frequency and large-scale roughness can be obtained. Discontinuity information may be synthesized for a much more representative geomechanical understanding of the rockmass than was previously impossible with traditional hand mapping limited by face accessibility. The alignment of Lidar scans from successive exposed faces offers additional interpretation and recording advantages, particularly where shotcrete is subsequently applied behind the face. In aligning scans, larger scale features can be readily identified and rockmass trends over several rounds may be identified. Discontinuity geometries and characteristics may be input into kinematic and numerical models for further analysis.