Remote monitoring of rock mass deformation using time domain reflectometry

Time Domain Reflectometry (TDR) has been used successfully for monitoring rock mass displacements, but there have been limitations due to the frequency with which cables could be interrogated and the manual techniques used for analysis of signature changes. Cables have failed in shear above the zone of caving and in advance of active longwall mining faces where it was expected that the rock mass would deform elastically. If it had been possible to interrogate cables several times daily, a more complete history of cable deformation prior to failure could have been obtained and a better explanation of rock mass behavior would be possible. It is significant then that cable testers are now being used by the Bureau of Mines that can be controlled remotely and allow for real time display, storage, and analysis of signature changes. Consequently, cables can be interrogated as frequently as desired, maximizing the amount of information obtained before a cable is severed. Examples of TDR monitoring over a coal mine and within a potash mine are presented to demonstrate the necessity of frequent data acquisition for purposes of interpreting rock mass behavior.