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

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

NIOSH – Short Base-Length Resistive Foil Strain Gauges Coal 0.9m 1.4m 1.3m 1.5m 1.0m Mudstone rock 15 31 83 106 68 101 8 26 107 100 7 11 38 98 56 129 6 75 99 85 67 116 5 AXIAL LOAD, kN 1.8 m 2 -8 -17 -21 53 -2 -12 -5 -13 -18 -170 -1 4 -4 -57 1 -32 78 37 BENDING LOAD, N-m 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.

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

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)

Long Base-length – Rebar Arrays

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)

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?

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

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

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

Symmetric Point Load

Symmetric Point Load Experiment Theory

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

Cantilever Load Experiment Theory

Pull-Test

Pull-Test Full Length Embedment Length

Pull-Test

Double Shear Configuration Direction of applied force

Double Shear Configuration

Shear Couplet

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

Comparison of Methods Foil Strain Gauge Long Base-length Inductive   Foil Strain Gauge Long Base-length Inductive Distribute Optical Cost/Instrument ~$2800+ ~$1000 ~$800 Cost/Strain Point 140+ 160+ <$1 Cost/Readout Unit $1000+ $300 $50,000 (was $250,000 in 2005) Data-Logging Yes Yes: but only two instruments/readout Data-Logging Frequency 1/s 0.1/sec 10/sec Intrinsically Safe Requires Investment Yes: Analyzer 120ft away in clean air Type Monitoring Inspection AIMS 2012 Rock Bolting and Rock Mechanics in Mining

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

Thank You Questions?