High Frequency Fibre Bragg Grating Interrogator for Monitoring Rock Cracking Events for Mining Applications

Acoustic Emission/Micro-seismic monitoring of cracking of rock or rock mass is important for assessing the integrity of rock mass and to take necessary precautions in the stability analysis of underground and open pit geomechanical structures. Micro-mechanics of deformation of rock and precursors to major failure or rock bursting mechanisms can be best understood in the laboratory under controlled stress conditions. An experimental program was envisaged to understand and monitor the stress induced cracking events during compressive loading of two rock specimens of different geometry shapes. High frequency Fibre Bragg Grating (FBG) based optic fibre interrogator system was used to monitor Acoustic Emission (AE) of rock specimens under two different test configurations. The FBG sensors picked up high frequency AE events of rock cracking, and these captured AE events predominantly coincided with the load drops in the load-time/deformation diagrams. These high frequency FBGs optic fibre interrogator systems could be used as an alternative to PZT/geophone based systems and they can be safely deployed in underground mines and AE can be monitored over a long distance with least transmission loss.