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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 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 mines or karst features, such as caves or caverns resulting from the chemical dissolution of carbonate rocks such as limestone or dolomite. Worldwide, sinkholes may vary in size from 1 to 600 meters (3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly.

Sinkhole and soil settlement

Large Geotechnical critical areas Lack of effective monitoring that can provide full / nearly full coverage SENSING 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

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 DiTeSt - Brillouin scattering effects The Brillouin frequency shift B is directly proportional to the acoustic velocity V A, which in turn is directly related to the material density, which is temperature T and strain  dependent. Scattering medium Laser, o Brillouin Frequency Shift: B = 2 nV A / B ( T,  ) depends on temperature and strain

F F  T1T1 Position [m] Strain [  ] DiTeSt STA-SMA Reading Unit Distributed Sensor 0m 1m 100m 1000m 50km T1T1  T2T2 T2T2 Position [m] Temp. [°C] DiTeSt ® STA – SMA System

 Measurement range: km per channel (depending on selected strain sensor)  Spatial resolution: min. 0.5 m (5 ns pump pulse width)  Distance resolution 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% = = 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, , SMS, acknowledge via SMS Remote connection and assistance Data display on maps DiView Software

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” Sensor Geotextile

Polytect FP6 - EU project Inflating balloon Vertical displacement meters

Polytect FP6 - EU project Zero condition Simulated settlement

Polytect FP6 - EU project Typical differential analysis plot

Polytect FP6 - EU project Controlled settlement  Settlement zone  5 m

Bigger settlement  Hiher strain in sensor Polytect FP6 - EU project

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

Quay-wall monitoring project 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 Quay-wall monitoring project De-soilment area

Cable maintenance in settlement area Quay-wall monitoring project

Sinkhole monitoring project Hutchinson – Kansas – USA Subsidence sink-hole monitoring project January 2010

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

Sinkhole monitoring project Digging of the trench were the sensor is deployed

Sinkhole monitoring project Site operations Site quality check

Sinkhole monitoring project Site pulling different locations

Sinkhole monitoring project 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

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