UAV-based Underground Digital Photogrammetry for Geotechnical Characterization of Fractured Rock Masses

Montana Technological University, Butte MT

Investigators

Abstract

Accurate geologic and geotechnical information, particularly orientation of rock fractures, is critical for the design of safe underground openings. Large, irregular mine openings known as "stopes" are particularly susceptible to collapse due to inadequate geotechnical data, but accurate data are scarce because access is often unsafe, and because of the limitations of other available tools (LiDAR and ground-based photogrammetry). With recent advances in unmanned aerial vehicles (known as UAVs, or drones), UAV-based digital photogrammetry has the potential to allow high quality geotechnical characterization of these large, unsupported underground openings if the challenges associated with lighting, flight control, and image georeferencing can be overcome. This research will address these issues, and a suite of indoor and field experiments to pilot test the system will be conducted. The results of this research have the potential to benefit society by enhancing safety in the mining and underground construction industries, and have potential application in a wide variety of other fields ranging from disaster response (inspection of collapsed or damaged buildings), to exploration of enclosed spaces (caves, storage tanks, ships, etc.) and documentation of sensitive historic structures. The primary goal of this project is to develop a UAV-based digital photogrammetry system to be used as a tool for geotechnical characterization of inaccessible underground (unlit) sites. The system would be able to capture good quality photos (well-lit, not blurry) with adequate overlap to provide stereo coverage. This requires assembly of a UAV that can carry the equipment to take the images as well as the required lighting and batteries, and that can be guided to precisely controlled locations. Options that may be investigated include video vs. still images, ambient vs. flash lighting, and piloted vs. autonomous guidance systems. Additionally, a number of control points are required to establish a georeferenced 3D model from sets of photos; a system for establishing those control points will also be developed and tested. The system will be tested in indoor spaces on the Montana Tech campus and in the field at a nearby underground mine. The accuracy of the 3D models of the indoor and underground spaces, including orientations of fractures in the rock mass at the field site, will be quantified. The project will provide excellent opportunities for the PI and students to interact with representatives from the mining industry, and with personnel from the NIOSH Spokane Research Laboratory (which is focused on mine safety and health research). It will also establish the infrastructure for researchers in the Department of Geological Engineering to contribute to future research projects involving UAV-based data collection, and for the students involved in this research to have access to this state-of-the-art technology.