Dynamic, high-quality measurements of displacements can be made in real-time using video monitoring, even in situations that do not allow access or instruments. Video monitoring uses pattern-recognition technology (i.e. digital image correlation) to track displacements within recorded videos and has a measurement resolution and accuracy equivalent or better than conventional instruments. This emerging technology is versatile and has been successfully applied to a wide range of rock mechanics problems in underground mines. After a roof-mounted conveyor pulley assembly in a salt mine fell due to bolt failure, a video monitoring investigation was completed to characterize the displacements the pulley assemblies and conveyor drives undergo during startup and typical operation. The displacement measurements were used to schedule maintenance and improve the startup procedure of the drives. In another case study, the deflection of a salt bridge with a speed and load limit was measured to determine if the limits were appropriate. The technology is also being developed as a ground-hazard warning system. The system can automate video collection and processing to export mine displacement measurements remotely. Tests have been performed at the Sanford Underground Research Facility (SURF), the former Homestake Gold Mine, and at an active potash mine in New Mexico. Multiple cameras, each capable of monitoring a 100-meter length of mine drift, have demonstrated a measurement resolution of 0.1 mm. The advantages of video monitoring over rock mechanics instruments (e.g. closure poles or extensometers) are that video monitoring provides numerous measurement points, the measurement points can be added or relocated after the video is recorded and the displacements can be post-processed, and the system is unobtrusive.
