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A.J.Hyett 1 B.J. Forbes 1 A.J.S . Spearing 2

Enlightening Bolts Using Distributed Optical Sensing to Measure the Strain Profile along Fully Grouted Rock Bolts. A.J.Hyett 1 B.J. Forbes 1 A.J.S . Spearing 2. Rock Bolt Progression. Constraints Safety & Costs. Design Model. Capacity. D emand. Rock Bolting Optimization C ycle.

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A.J.Hyett 1 B.J. Forbes 1 A.J.S . Spearing 2

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  1. Enlightening BoltsUsing Distributed Optical Sensing to Measure the Strain Profile along Fully Grouted Rock Bolts A.J.Hyett1 B.J. Forbes1 A.J.S. Spearing2

  2. Rock Bolt Progression Constraints Safety & Costs Design Model Capacity Demand Rock Bolting Optimization Cycle Feedback Communication Verify Installation Observation Quality Control Instrumentation Implement Modified after Diederichs and Hutchinson (1993) AIMS 2012 Rock Bolting and Rock Mechanics in Mining

  3. NIOSH – Short Base-Length Resistive Foil Strain Gauges AXIAL LOAD, kN 6 7 5 8 11 26 15 15 38 75 31 31 1.8 m Mudstone rock 98 83 99 83 129 100 116 101 106 107 85 106 68 31 67 56 Coal 0.9m 1.4m 1.3m 1.5m 1.0m BENDING LOAD, N-m 6 Signer SD, Cox D and Johnson J. A method for the selection of rock support based on loading measurements In: Proceedings of the 16th International Conference on Ground Control in Mining. Morgantown (WV); 1997. p. 183–90. 8 5 7 2 1 -12 4 -4 -5 5 -8 1.8 m Mudstone rock 0 -13 0 -17 -1 1 37 -2 0 -18 -32 -21 53 -170 -57 78 Coal 0.9m 1.4m 1.3m 1.5m 1.0m

  4. Long Base-length Inductive Strain Gauges • Typical base-length of 200-500mm • Discrete “zones” • Capable of monitoring load on any section of the rebar

  5. Long Base-length – Strain Contour Mapping Four Instrumented Bolts at the Mid Pillar of a Room and Pillar mine • Strain localize towards center of mid pillar heading • Visualize “stretch arch” με scale 1500 με = 100kN (or 10 tons)

  6. Long Base-length – Rebar Arrays

  7. Long Base-length – Rebar Arrays • Readings taken: • 09/07/2010 11:00 • Readings taken: • 09/07/2010 17:00 με scale • Steel rebar • Steel rebar 1500 με = 100kN (or 10 tons)

  8. Long Base-length - Limitations • 1. Not Intrinsically Safe (IS approved) • 2. Limited spatial resolution along the bolt • 3. Not designed to measure shear Does a technology exist that can overcome these limitations?

  9. Objective • Validate the use of fiber-optic technology for rock bolt instrumentation • Develop a superior marketable product for monitoring and safety services

  10. Testing • Developing a prototype Diametrically opposed grooves along the length of a Rebar Bolt Run fiber- optic instrumentation along the grooves in Rebar

  11. Testing • Point Load Bending (Symmetric and Cantilever) • Axial Pull-Test (Short Embedded Length) • Double Shear Configuration

  12. Symmetric Point Load

  13. Symmetric Point Load Experiment Theory

  14. Cantilever Load Direction of applied load 0.2m Embedment length in concrete block (held in place)

  15. Cantilever Load Theory Experiment

  16. Pull-Test

  17. Pull-Test Embedment Length Full Length

  18. Pull-Test

  19. Double Shear Configuration Direction of applied force

  20. Double Shear Configuration

  21. Shear Couplet

  22. Summary of Tests • Fiber-Optic instrumentation is fundamentally viable • Output data from experiments compare within ± 5% of theory • The shape of experiment and theory plots are essential identical

  23. Comparison of Methods AIMS 2012 Rock Bolting and Rock Mechanics in Mining

  24. Major Conclusions • Fiber-Optic instrumentation is the future of ground monitoring: - Higher Resolution and increased Accuracy - Cheaper and less Difficult to manufacture • Improved empirical correlations: - More accurate modeling = increased productivity - More accurate monitoring = Workplace Safety

  25. Thank You Questions?

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