A.J.Hyett 1 B.J. Forbes 1 A.J.S . Spearing 2
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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
description
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. - PowerPoint PPT Presentation
Transcript of A.J.Hyett 1 B.J. Forbes 1 A.J.S . Spearing 2
Enlightening BoltsUsing Distributed Optical Sensing to Measure the
Strain Profile along Fully Grouted Rock Bolts
A.J.Hyett1 B.J. Forbes1A.J.S. Spearing2
AIMS 2012 Rock Bolting and Rock Mechanics in Mining
Verify
DesignModel
ConstraintsSafety & Costs
Capa
cityDem
andImplement
Communication
Inst
allat
i
on
Quality Control
Rock BoltingOptimization
CycleObs
erva
tionInstrum
entation
Feedback
Modified after Diederichs and Hutchinson (1993)
Rock Bolt Progression
NIOSH – Short Base-Length Resistive Foil Strain Gauges
Coal
0.9m 1.4m 1.3m 1.5m 1.0m
Mudstone rock
1531
83
10668
101
82631
83
10731
100
7
1138
98
10656
129
6
1575 99
85 67
116
5AXIAL LOAD, kN
1.8
m
Coal
0.9m 1.4m 1.3m 1.5m 1.0m
Mudstone rock
2
-8-17
-2153
-2
8
-12-5-13
-18-170
-1
7
4-4
0
0-57
1
6
15
0
-32 78
37
5BENDING LOAD, N-m
1.8
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 InternationalConference on Ground Control in Mining. Morgantown (WV); 1997. p. 183–90.
Long Base-length Inductive Strain Gauges
a. Stacked Configuration
Sensor 1Sensor 3Sensor 5
Sensor 2Sensor 4Sensor 6
Side A
Side B
b. Staggered Configuration
Sensor 1Sensor 3Sensor 5
Sensor 2Sensor 4Sensor 6
Side A
Side B
- Typical base-length of 200-500mm
- Discrete “zones”
- Capable of monitoring load on any section of the rebar
Long Base-length – Strain Contour Mapping
- Strain localize towards center of mid pillar heading
- Visualize “stretch arch”
με scale
1500 με = 100kN (or 10 tons)
Four Instrumented Bolts at the Mid Pillar of a Room and Pillar
mine
Long Base-length – Rebar Arrays
Long Base-length – Rebar Arrays
1 2 3 4 5
Nod
e Lo
catio
n
1
2
3
4
5
6
7
Heading #6
Heading #7 Intersection
100555077
100555074
100555071
100555075
100555078
Nod
e po
sitio
n
1
2
3
4
5
6
7
Heading #6
Heading #7 Intersection
100555078
100555074
100555075
100555071
100555077
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
με scale
1500 με = 100kN (or 10 tons)
Steel rebar
Steel rebar
Readings taken: 09/07/2010 11:00
Readings taken: 09/07/2010 17:00
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
0.2m Embedment length in concrete block (held in place)
Direction of applied load
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
AIMS 2012 Rock Bolting and Rock Mechanics in Mining
Comparison of Methods
Foil Strain GaugeLong 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 YesYes: but only two
instruments/readout
Data-Logging Frequency 1/s 0.1/sec 10/sec
Intrinsically Safe Yes Requires InvestmentYes: Analyzer 120ft
away in clean airType Monitoring Monitoring Inspection
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 YouQuestions?
