Development and testing of the CMIN-BCM for monitoring borehole closure in underground environments

ABSTRACT: Monitoring borehole deformation during underground excavation activities is one method of evaluating rock mass performance during mining and tunneling. Continued monitoring and comparison to anticipated rock mass behaviour and/or existing stress models are important components of the engineering design and verification process. A comprehensive monitoring program provides real-time feedback of in situ rock behavior and delivers an added level of safety monitoring for underground works. Furthermore, accurate monitoring of borehole deformation can also be used to estimate changes to the induced stress field, and in turn, potential back analysis of the far field stress regime. CanmetMINING has developed a robust tool, referred to as the CanmetMINING Borehole Closure Meter (CMIN-BCM), for accurate and precise measurement of borehole deformation. The instrument, designed for use in 60 mm diameter boreholes, has a maximum range of 6.0 mm, resolution of 0.05 µm and accuracy of 5 µm over its full range. This paper presents a summary of instrument development and its specifications, as well as the results of bench scale and rock block laboratory testing. Future testing and development of the instrument will include a field testing program, including underground installation to monitor in situ conditions, as well as modifications to the external components of the instrument to increase its ability to withstand harsh field conditions. © 2019 Copyright reserved, Natural Resources Canada