We will start shortly…. Detection and localization of sinkholes and soil settlements with distributed sensing Presented by: Riccardo Belli – PLM Distributed

We will start shortly…

Detection and localization of sinkholes and soil settlements with distributed

sensing

Presented by: Riccardo Belli – PLM Distributed System

Web Seminar

• You should hear my voice through your PC speaker / headset

• You can ask questions using the “Questions” panel on the right of your screen. We will answer:

• In the “Questions” Panel• At the end of the presentation• By email

• Later this week you will receive link to:• Presentation in PowerPoint, PDF and with narration• Datasheets

Contents

• Introduction / motivations to soil settlements

and sinkhole openings Monitoring with

Distributed Fiber Optic Sensors

• Technology

• Application Examples

• Questions and Answers

Sinkhole and soil settlement

Sinkholes, also known as dolines or cenotes,are depressions or holes in the Earth's surface

caused by collapse of either underground minesor karst features, such as caves or cavernsresulting from the chemical dissolution of

carbonate rocks such as limestone or dolomite.Worldwide, sinkholes may vary in size from 1 to600 meters (3 to 2,000 ft) both in diameter anddepth, and vary in form from soil-lined bowls to

bedrock-edged chasms. Sinkholes may formgradually or suddenly.

Sinkhole and soil settlement

• Large Geotechnical critical areas

• Lack of effective monitoring that can provide full / nearly full coverageSENSING EVERYWHERE

• Limited capabilities of conventional sensors, mainly in localize the settlement and cover the critical area

• Limited possibility of predicting sinkhole opening or soil settlement, definition of effective sensors network

• Provide early stage detection and fast reaction

• Increasing safety awareness

• 24 / 7 automatic monitoring and alert triggering

• Remote control

Motivations

Motivations

Traditional sensing

?

Motivations

Anomaly occurence

?

Sensing everywhere

Motivations

Sinkhole & Settlement Monitoring Goals

• Localization of abnormal soil movements• Analysis of sinkhole and soil settlement evolution• Threshold monitoring• Detection of early stage sinkhole and soil settlement• Precise localization over wide areas

SENSING EVERYWHERE• Default prevention

Technology

Distributed Sensing

• Single fiber optic sensor (sensing cable)

• Every segment of sensing cable replaces a discrete

sensor (typically a long gage sensor)

• Provides for location (where?) and magnitude

(how much?) of measurand (average strain and/or

average temperature)

• Complete measurand profile obtained by single

scan

T, ε T, ε

DiTeSt - Brillouin scattering effects

The Brillouin frequency shift B is directly proportional to the acoustic velocity VA, which in

turn is directly related to the material density, which is temperature T and strain dependent.

Scattering medium

Laser, o

Brillouin FrequencyShift:

B = 2nVA /

B(T,) depends ontemperature and

strain

FF

T1

Position [m]

Str

ain

[]

DiTeSt STA-SMA Reading Unit

Distributed Sensor0m

1m 100m

1000m

50km

T1

T2

T2

Position [m]

Te

mp

. [°C

]

DiTeSt ® STA – SMA System

DiTeSt ® STA – SMA System

Measurement range: 0 - 50 km per channel (depending on selected strain sensor)

Spatial resolution: min. 0.5 m (5 ns pump pulse width)

Distance resolution m @ full range: 0.1 m (depending on spatial resolution)(sampling rate – 1 point every 0.1 m)

Number of locations: up to 100’000 distance points

Acquisition time: minutes (typical)

Number of channels: 2

Multiplexer: from 4 up to 20 channels

DiTeSt SMARTprofile Sensor

• 2 fibers for strain sensing and 2 for interconnection (if applied for settlement and sinkhole monitoring)

• Encapsulation in a Polyethylene PE profile

• Strain range: 1% = 10000 = 10 mm/m

• Direct soil or geo-textile embedding

• Optical losses ~ 1.0 dB/km

DiTeSt SMARTube Sensor

• Improved and reliable design

• Dimensions: 5.34 mm outer tube, 2.8 mm inner tube

• Optical losses ~ ≤ 2.0 dB/km

• Good mechanical reliability

5.34

mm

2.8 mm

• Management of distributed measurement data

• Strain measurement analysis of single and multiple

sensors

• System Status Management

• Automatic and schedule measurements 24 / 7

• Alarm triggering

• Warnings based on threshold and rate conditions

• Voice message, e-mail, SMS, acknowledge via SMS

• Remote connection and assistance

• Data display on maps

DiView Software TT

Settlement working principle

• Buried distributed strain sensor over the selected critical area – sensing everywhere with single cable

• Sinkhole or soil settlement induces strain over the sensing cable by stretching the fiber

• DiTeSt STA-SMA detects strain variations / evolution and localize it on the distributed sensor

• DiView data management software visualizes the anomaly on a map

• DiView data management software automatically triggers an alert and send mail or sms message at selected recipient

Applications examples

Polytect FP6 - EU project

0.5 m

5 m

4 m

0.4 m

Sand

Controlled Settlement

area

Displacement meter (LVDT)

“Bath”

SensorGeotextile


Inflating balloon

Vertical displacement meters


Zero condition Simulated settlement


Typical differential analysis plot


SMARTprofile, F1

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

13 14 15 16 17 18 19 20 21 22

position [m]

Ave

rag

e st

rain

[ ]

4.09 mm 42.17 mm

58.67 mm 64.97 mm

76.68 mm 80.82 mm

90.32 mm 90.32 mm

90.32 mm 90.32 mm

93.26 mm 96.80 mm

107.38 mm 115.41 mm

119.67 mm 130.95 mm

133.38 mm 139.76 mm

Con

trolled

sett

lem

en

t

Settlement zone

5 m

SMARTprofile F1

y = 66.98x - 303.61

R2 = 0.97

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Vertical settlement [mm]

Ave

rag

e st

rain

in

set

tlem

ent

po

int

(co

ord

inat

e 17

.91m

) [

]

Bigger settlement Hiher strain in sensor



Quay-wall monitoring project

• DiTeSt STA-SMA • 2 SMARTprofile monitoring lines, 580 m each• DiView 24 / 7 automatic software• Soil stability • Abnormal de-soilment detection and localization


• SMARTprofile Distributed Strain Sensor directly embedded into soil during construction phases with the aim to detect abnormal de-soilment and analyze the evolution of soil settlement.

• Continuous automatic monitoring from the construction to the operation.

• Effective detection and localization of settlement area and of abnormal de-soilment during early operational phases.

DiView software GUI


De-soilment

area

Cable maintenance in settlement area


Sinkhole monitoring project

Hutchinson – Kansas – USASubsidence sink-hole monitoring projectJanuary 2010


A total of 4 km of Strain Distributed Sensor dicertly buried into soil


Digging of the trench were the sensor is deployed


Site operations

Site quality check


Site pulling test @ different locations


DiView software GUI

Project Pubblications

Smart Textiles for SHM of Geostructures and Buildings

Localization of instability zones in levees, landslides, sinkholes and tunnels with

distributed optical fiber sensors

Salt cavern monitoring system for early warning of sinkhole formation

Conclusion

• Soil settlement evolution and sinkhole formation monitoring

• Detection and localization of soil settlement and sinkhole formation over long distances

• Detection and localization of sinkhole formation at early stage

• Reliability in demanding environments

• Extended measurements range

• Cost effective

• On-line permanent monitoring

• Powerful and versatile software for data management and intelligent alerts

Pipeline Integrity Monitoring

Thank you for your attention

For more informationwww.roctest-group.com

Thank you for your attention

Documents

We will start shortly…. Detection and localization of sinkholes and soil settlements with distributed sensing Presented by: Riccardo Belli – PLM Distributed