The Application of Distributed Optical Strain Sensing to Measure Rock Bolt Deformation Subject to Bedding Shear
Shear displacement along bedding defects is a well-recognised behaviour when tunnelling and mining in stratified rock. This deformation can affect the durability and integrity of installed rock bolts. In-situ monitoring of rock bolt deformation under bedding shear cannot be accurately derived from traditional strain gauge bolts as sensors are too large and spaced too far apart to accurately assess concentrated displacement along discrete defects. A possible solution to this is the use of fiber optic technologies developed for precision monitoring. Distributed Optic Sensor (DOS) embedded rock bolts were installed in a tunnel project with the aim of measuring the bolt deformation profile under significant shear displacements. This technology successfully measured the 3D strain distribution along the bolts when subjected to bedding shear and resolved the axial and lateral strain constituents in order to determine the deformational geometry of the bolts. The results are compared well with the current visual method for monitoring shear displacement using borescope holes, considering this method as suitable.
 R. Bertuzzi. 100- Year design life of rock bolts and shotcrete. Ground Support in Mining and underground construction- Villaescusa and Potvin (eds) 2004 246-249
 A. M Ferrero.. The shear strength of reinforced rock joints. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995. 32: 595–605.
 B. Forbes, N, Vlachopoulos and A. J. Hyett. The application of distributed optical strain sensing to measure the strain distribution of ground support members. 2018. FACETS. 3: 195–226. DOI: 10.1139/facets-2017-0093
 B. Forbes, N, Vlachopoulos, A. J. Hyett and M. S. Diederichs. A new optical sensing technique for monitoring shear of rock bolts. Tunnelling and Underground Space Technology, 2017. 66: 34–46. DOI: 10.1016/j.tust.2017.03.007
 G. Grasselli. 3D behaviour of bolted rock joints: experimental and numerical study Int. J. Rock Mech. Min. Sci. 2005. 42, 13–24.
 U. Hesterman, L-P. Calbrix, C Bodner. NorthConnex – A New Perspective for Tunnelling in Sydney. 16th Australasian Tunnelling conference 2017.
 CC. Li, G. Kristjansson and A.H. Høien. Critical embedment length and bond strength of fully encapsulated rebar rockbolts. Tunneling and Underground Space Technology 2016;59:16e23.
 E. McHugh and S. Signer. Roof bolt response to shear stress: laboratory analysis. In Proceedings of the 18th International Conference on Ground Control in Mining, Morgantown, West Virginia. 1999; pp. 232–238.
 D. Nicholson, C-M. Tse and E. I. C. Penny. CIRIA Report 185. The Observational Method in ground engineering: principles and applications. 1999.
 L. B. McQueen. In situ rock stress and its effect in tunnels and deep excavations in Sydney. Australian Geomechanics, 2004; 39(3), pp.43-57
 D. Oliveira and M.S. Diederichs. Tunnel support for stress induced failures in Hawkesbury Sandstone. Tunnelling and Underground Space Technology. 2007; 64, pp.10-23.
 P.J.N. Pells, G. Mostyn and B.F. Walker. Foundations on sandstone and shale in the Sydney region. Australian Geomechanics; 1998; Vol 33(3):17–29.
 D. Tepavac, P. Mok, D. Oliveria, H. Asche, Y. Sun and S. Simmonds. High In-Situ Stress and its Effects in Tunnel Design: An Update Based on Recent Project Experience from WestConnex M4 East & New M5 Tunnel, Sydney Australia. 16th Australasian Tunnelling conference 2017, 375-386
 E. Villaescusa, E. Hassel and R. A. Thompson. Corrosion of rock reinforcement in underground excavations. Minerals and Energy research institute of Western Australia. Report No. 263. 2007.
 N. Vlachopoulos, D. Cruz and B. Forbes. Utilizing a novel ﬁber optic technology to capture the axial responses of fully grouted rock bolts. Journal of Rock Mechanics and Geotechnical Engineering 10 (2018) 222-235
 B. Forbes, N. Vlachopoulos, M.S. Diederichs, A. J. Hyett. 2018. Spile support performance monitored in a shallow urban tunnel using distributed optical strain sensing, in: 52nd U.S. Rock Mechanics/ Geomechanics Symposium. Seattle, Washington, p. 8.