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Hiroshi Naruse, Mie University Japan
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Overview of fiber optic sensing system: BOTDR and its applications
Hiroshi NaruseMie University
June 12, 2008 in Santiago, Chile
Hiroshi Naruse, Mie University Japan
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Introduction of Mie University
Five Graduate Schools and Undergraduate Faculties- Humanities and Social Sciences- Education- Medicine- Engineering-Bioresources
There are about 70 national universities in Japan.Mie University is one of them and a middle scale university.
Location of Mie University.
Number of studentsUndergraduate : 6212Postgraduate : 1182Total : 7394
Hiroshi Naruse, Mie University Japan
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Air view of Mie University
My office
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system
2. Optical fiber sensors
- Embedded type
- Attached type
3. Applications to the monitoring of practical civil structures
- Concrete beams
- Cast-in-place concrete piles
- Railway tunnels
- Underground mine tunnels
Hiroshi Naruse, Mie University Japan
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Configuration of fiber optic sensing system
Fiber optic sensing system
Measuring device
Optical fiber sensor
Optical fiber itself
Sensing element processed optically or mechanically so that it is sensitive to various physical quantities
Hiroshi Naruse, Mie University Japan
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Classification of fiber optic sensing systems
2. Distributed sensing systems(Entire optical fiber acts as both sensing element and signal transmission line.)
Measuring device
Optical fiber
Transmission Sensing element
Measuring device
Optical fiber
Transmission and sensing
1. Discrete-point sensing systems(Only part of the optical fiber acts as a sensing element; the rest is used as a
signal transmission line.)
Only information from sensing elements
Information from everywhere along the fiber
Hiroshi Naruse, Mie University Japan
Optical fiber
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Typical discrete-point sensing systems
Fiber Bragg grating (FBG) system
- Filter sensor- Strain/temperature measurement based on frequency shift reflected from FBG
Optical fiber
Core
Clad
Bragg grating
Measuring device
Measuring device
Displacement
- Displacement measurement based on attenuation in this part of the optical fiber
Optical loss conversion sensing system
Bending
Sensing elementSensing element
Hiroshi Naruse, Mie University Japan
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Distributed sensing system
Distributed sensing system- information at effectively continuous points along the fiber- some variations depending on the combination of
(i) physical phenomenon used for measurement and(ii) method used for determining measurement position in the optical fiber.
Some distributed strain/temperature measuring devices are commercially available.
Hiroshi Naruse, Mie University Japan
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Physical phenomena used to measure strain/temperature
Rayleigh scattering(loss measurement)
Brillouin scattering(strain and temperature measurement)
Raman scattering(temperature measurement)
Incident light
Optical frequency
11 GHz
13 THz
Intensity changeSc
atte
red
light
pow
er
Frequency shift
Hiroshi Naruse, Mie University Japan
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Method of determining observed position in optical fiber
- OTDR: Optical Time Domain Reflectometry
Pulsed light launched
Backscattered light
Core Clad Optical fiber
t
tPulsed light position(position where light is scattered)
- Light scattering position is determined from light velocity andelapsed time from launch to detection
- By sampling elapsed time at short intervals, we can obtain distributed measurement of scattered light power spectrum every few centimeters.
- Scattered light power spectrum & position where it is produced
Hiroshi Naruse, Mie University Japan
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Power spectrum along optical fiber obtained by BOTDR
Brillouin backscattered light
Pulsed lightΔz
Lightsource
BOTDR
∝ strain εPower spectrum at each distance
Pulsed light launching
Strain
Optical fiber
Bril
loui
n ba
cksc
atte
red
light
pow
er
ε0
0
DistanceOptical fre
quencyνB(0)
νB(ε)z1
z2
νB(ε) = νB(0) + Cs ε
Peak power frequency: νB(ε), νB(0)
Cs: Coefficient(strain frequency shift)
Receiver
Strained section
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system
2. Optical fiber sensors
- Embedded type (jointly with Institute of Technology and Shimizu Corporation)
- Attached type
3. Applications to the monitoring of practical civil structures
- Concrete beams
- Cast-in-place concrete piles
- Railway tunnels
- Underground mine tunnels
Hiroshi Naruse, Mie University Japan
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Structure of optical fiber sensor
Steel wire
Ordinary 4-fiber ribbon telecommunication optical fiber
Plastic sheath
Attenuation: 0.25 dB/km
Attached optical fiber sensor for sensing strain
Hiroshi Naruse, Mie University Japan
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Mounting bracket
Nut with notch
Notches
A’
A
Optical fiber sensor
Divided plastic boltCross-section A-A’
Structure of sensor fixing unit
Optical fiber sensor attached to inner surface of tunnel by fixing unit
Hiroshi Naruse, Mie University Japan
15Embedded optical fiber sensor for sensing strain
Fiber reinforced plastic
Resin coat Optical fiber
Fiber reinforced plastic(FRP)
Resin coat
2–6 mm
0.25 mm
Optical fiber(UV coat)
Merits
- Easy installation- High reliability
(fixed without glue)- High sensitivityEmbedded strain-sensing fiber
Steel bar
Fixing fiber to steel bars
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system2. Optical fiber sensors
- Embedded type- Attached type
3. Applications to the monitoring of practical civil structures- Concrete beams(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Cast-in-place concrete piles(jointly with Hokkaido Development Bureau, Civil Engineering Research Institute)
- Railway tunnels(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Underground mine tunnels(jointly with CODELCO, Chile)
Hiroshi Naruse, Mie University Japan
Concrete beam
Load
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Concrete beam
Embedded sensor
Load
Load0.4 m
0.5 m 1 m3 m
Steel barStrain gauge (0.3 m interval)
Embedded optical fiber sensorBOTDR
Concrete beam bending-strain measurement by embedded sensor
Hiroshi Naruse, Mie University Japan
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Embedded optical fiber sensor
Strain gaugeLower
Upper
Position along concrete beam (m)0 1 2 3
Mea
sure
d st
rain
(x10
-3)
0
1
2
3
-1
Load points
Theoretical strain distribution
Beam
Concrete beam bending-strain measurement results
(Trapezoid)
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system2. Optical fiber sensors
- Embedded type- Attached type
3. Applications to the monitoring of practical civil structures- Concrete beams(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Cast-in-place concrete piles(jointly with Hokkaido Development Bureau, Civil Engineering Research Institute)
- Railway tunnels(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Underground mine tunnels(jointly with CODELCO, Chile)
Hiroshi Naruse, Mie University Japan
Hammer grab
20Construction of cast-in-place concrete pile by all-casing method
Bedrock
Steel pipe
Concrete
Shovel
Steel tube
Steel cage
knocking-in of steel pipe Removal of
inside soil
Installation of steel cage
Concrete pouring
Hiroshi Naruse, Mie University Japan
21Application to load-testing of cast-in-place concrete piles
Groove
16 mm5 mm
Optical fiber sensor (diameter: 0.9 mm)
Bonding agent
Steel bar
Test pile
Hydraulic jacks
Reaction pile Optical fiber sensor
Appearance of the test
Optical fiber sensorDepth: 11 m
Diameter: 1.2 m
Reinforced steel bar
ConcreteBOTDR
Test pile
Load
Ground level
Additional steel bar
Hiroshi Naruse, Mie University Japan
22Measured and theoretical strains
-6 -4 -2 0 2
1600tons
0
2
4
6
8
10
Theoretical
Measured
Dep
th fr
om to
p of
pile
(m)
Strain (x10-4)
400
800
1200
Load
BOTDR
Sensing optical fiber11 m
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system2. Optical fiber sensors
- Embedded type- Attached type
3. Applications to the monitoring of practical civil structures- Concrete beams(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Cast-in-place concrete piles(jointly with Hokkaido Development Bureau, Civil Engineering Research Institute)
- Railway tunnels(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Underground mine tunnels(jointly with CODELCO, Chile)
Hiroshi Naruse, Mie University Japan
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Concrete pipe strain measurement
Concrete pipe
2.3 m
Hydraulic jack
Loading point(0)
Load-bearing point(-180, +180)
3.5
m
3 m
Ordinary nylon-coated optical fiber
Hiroshi Naruse, Mie University Japan
51 tons
41 tons
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Measured strain distribution
-180 -90 0 90 180
-5
510
15
0
Stra
in (
x10-4
)
-5
51015
0
Stra
in (
x10-4
)
Angle (degrees)
Concrete pipe
Optical fiber
Loading point(0)
Load-bearing point (±180)
AB
C
DE
Stra
in (
x10-
4)
-180 -90 0 90 180
A B C D E
-1
-0.5
0
0.5
1
Angle (degrees)
AB
CD
E
AB
CD
E
Theoretical strain distribution
Load: 20.4 tons
Hiroshi Naruse, Mie University Japan
26Monitoring a railway tunnel under construction
Tunnel entrance
8 m
BOTDR system applied to subway tunnel construction
Pipes to support soil above tunnel
Construction method
- Displacement measurement of soil above tunnel- Circumferential stress measurement of tunnel wall
Tunnel cross-section
Dug out
Steel support
Hiroshi Naruse, Mie University Japan
27Two types of optical fiber sensors installed in the tunnel
(i) Displacement sensor
Tunnel wall circumferential stress measurement by embedded sensor
Cross-section
Sensor appearance
Optical fiber
Steel pipe
Aluminum pipe
Two pairs
Displacement sensor installation
Steel material
(ii) Embedded sensor
12 m
Hiroshi Naruse, Mie University Japan
28Measured tunnel displacement and circumferential stress
Concrete stress of tunnel wall calculated from the measured strain
Compression
Tension
-5 0 5 5 0 -5Stress (MPa)
Optical fiber sensor
Stress meter
Results for displacement sensor
-4
0
4
8
0 2 4 6 8 10 12
OrdinaryFiber
Def
orm
atio
n (m
m)
Distance from the pipe edge (m)
Tunnel
Pipe
Hiroshi Naruse, Mie University Japan
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Contents
1. Outline of fiber optic sensing system2. Optical fiber sensors
- Embedded type- Attached type
3. Applications to the monitoring of practical civil structures- Concrete beams(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Cast-in-place concrete piles(jointly with Hokkaido Development Bureau, Civil Engineering Research Institute)
- Railway tunnels(jointly with Mitsubishi Heavy Industries, Ltd., Nagasaki R&D Center)
- Underground mine tunnels(jointly with CODELCO, Chile)
Hiroshi Naruse, Mie University Japan
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Field trial conducted in El Teniente underground mine
(installation of monitoring system)Diablo Regimiento area
- In cooperation with NTT (Japan) and CODELCO (Chile)- Purpose: investigate the possibility of using BOTDR to detect changes in the state of the mine caused by mining activities such as blasting and excavation
Hiroshi Naruse, Mie University Japan
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Vertical cross-section of Diablo Regimiento area
Excavation direction
Undercut zone
Production level
Transport level
Ventilation level
Drift
Undercut level
Preparation zone
Ventilation shaft
Crusher
Belt conveyer
Broken rock
Drawbell
Ore passLHD
Undercutting face
Pre-undercut panel caving method
Hiroshi Naruse, Mie University Japan
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Outline of underground mine monitoring system
Operation office
Personal computer
Telecommunication network
El Teniente mine
BOTDR Personal computer
Optical switch
Office in mine (monitoring station)
Chile
Japan
Telecommunication optical fiber cable (1.3 km)
Undercut levelProduction and transport levels
DestroyedRisk of accidents
Ventilation tunnel
AB Optical fiber sensor
Hiroshi Naruse, Mie University Japan
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Relative positions of undercut level and ventilation tunnel
Undercutting face
Expansion
Ventilation tunnel
Optical fiber sensorsExcavation
Imbalance zone of stress distribution
Changes- Undercutting face passing- Large-scale ore extraction
Hiroshi Naruse, Mie University Japan
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Cross-sections of ventilation tunnel
Lateral direction
Rockbolt
Ceiling
Rock surface Fixing unit
Sensor on ceiling
Span: 3 m
Monitored tunnel length: 210 m(total sensor length: 420 m)
Rock
Longitudinal directionRock
5.2 m
4.6 mSidewall
- Deformation of changes in the state of underground mine from elongation/contraction of each span
- Two lines of sensors Changes in horizontal and vertical directions
Sensor on sidewall
Hiroshi Naruse, Mie University Japan
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Appearance of ventilation tunnel after sensors were installed
Optical fiber sensor on ceiling
A
BOptical fiber sensor on sidewall
Hiroshi Naruse, Mie University Japan
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Optical fiber sensor attached to tunnel and cabinet in mine office
Steel pipe
Rockbolt
Sidewall
Optical fiber sensor
AdapterReinforcement
Mounting bracket
Split bolts and nuts
Optical fiber from tunnel
Optical switch
BOTDR
Personal computer
Screen monitor
Optical fiber sensor attached to tunnel
Cabinet installed in mine office
Hiroshi Naruse, Mie University Japan
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Length change at respective spansEl
onga
tion/
cont
ract
ion
[mm
]
Distance from the first rockbolt position [m]
-8
-4
0
4
8
12
Sidewall Ceiling
0 30 60 90 120 150 180
Nov. 10, 2005
Span A
Hiroshi Naruse, Mie University Japan
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Length change in span of A
System installation
May Jun. Jul. Aug. Sep. Oct.
Elon
gatio
n in
span
A [m
m]
0
2
4
6
8
Start of large-scale extraction
Passing of undercutting face
Approaching
ContinuedExcavation area expansion
Undercutting and drawbell constructionPartially underway
Nov.
Field trial
/2005
Hiroshi Naruse, Mie University Japan
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Summary
-Overviewed a fiber optic sensing system based on the BOTDR system and its applications.
- Distributed fiber optic sensing systems are a promising technology and useful for various industrial applications such as ones in the civil engineering and mining fields.
Hiroshi Naruse, Mie University Japan
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Distributed fiber optic sensing systems based on Brillouin scattering
BOTDR
BOTDA
BOCDA
Optical fiber
Measuring device
OTDR(pulsed light)
OTDR(pulsed and continuous lights)
Optical correlation(frequency and phase modulated continuous wave lights)
System Distance measurementConfiguration
Measuring device
Optical fiber
Hiroshi Naruse, Mie University Japan
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BOTDR configuration
Probe light
Laser light
source
Continuouswave light
Optical fiber sensor
Brillouin scattered light
Electrical heterodyne receiver
Pulse modulation unit
Pulsed light
Optical heterodyne receiver
Digital processor
Reference light
Electrical signal conversion
ν0
ν0
ν0-νB
ν0 ν0-νB
BOTDR
νB
ν0: Incident light frequencyνB: Brillouin frequency shift
(11 GHz)
Hiroshi Naruse, Mie University Japan
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Another BOTDR configuration
Laser light
source
Continuouswave light
Optical fiber sensor
Brillouin scattered light
Pulse modulation & frequency translationunit
Pulsed light
Optical heterodyne receiver & O/E
Digital processor
Reference light
Electrical signal conversion
ν0 ν0’ (=ν0+νB’-νB)≅ν0
ν0 ν0’
BOTDR
ν0-ν0’ ≅0 ν0: Incident light frequencyνB: Brillouin frequency shift
(11 GHz)ν0’ : Almost the same frequency as ν0νB’ : Almost the same frequency as νB
ν0+νB’Probe light
Hiroshi Naruse, Mie University Japan
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Typical applications of distributed fiber optic strain sensing system
Central office
Plant
Building
Dam
Bridge
River levee
ShipTelecommunication tunnel
Soil slope Tunnel
Underground mine
Pile
Concrete beam bending-strain measurement