Validation of Bare FBG Sensors in Monitoring Compressive Rock Mass Deformation

Geotechnical stability is a major concern for the long-term safety and integrity in underground coal mines.The major issues with the current roof stability monitoring system in underground coal mines include lackof systematic real time data recording scheme and using electrical sensing components that are notintrinsically safe in underground explosive workplace. Although an advanced system based on fibre opticsensing (FOS) technologies have increasingly drawn attention by mining industry, their applications in coalmines are still challenged by a number of factors, such as the survivability in large strain range, appropriatefibre encapsulation and installation methods and minimisation of measurement errors due to the straintransfer loss. This paper presents the results of preliminary experiment in developing fibre optic based roofstability monitoring system forunderground coal mines, including the validation of surface mounting bareFBGs in rock mass compressive test. The accuracy of the bare FBG sensors in measuring compressivestrain for rock mass are validated against the electrical strain gauges and linear variable differentialtransducer (LVDT). Using the stress-strain curve and Young’s modulus of the standard samples as areference, the experiment results show that the bare FBG and electrical strain gauges can provide accurateand reliable compressive strain measurements for material with different mechanical properties.