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Detecting Bridge Scour by Thermal Variations Across the Stream Bed

Detecting Bridge Scour by Thermal Variations Across the Stream Bed. July 19, 2000 Presented by Paul L. Sharp. Problems with Current Scour Detection Technology. The technology may be difficult or expensive to deploy

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Detecting Bridge Scour by Thermal Variations Across the Stream Bed

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  1. Detecting Bridge Scour by Thermal Variations Across the Stream Bed July 19, 2000 Presented by Paul L. Sharp

  2. Problems with Current Scour Detection Technology • The technology may be difficult or expensive to deploy • Current technologies may be susceptible to damage in the harsh waterway environment • Adverse conditions, such as debris accumulation, ice, suspended material, etc., may cause the device to fail

  3. Proposed New Approach to Scour Detection • Use thermal sensors to detect temperature variations across the stream bed • This approach has the potential to be less expensive and more durable than other technologies • The Tennessee Department of Transportation sponsored the University of Memphis to investigate this idea

  4. The temperature of the streambed remains relatively constant (typically the average yearly temperature for the area) Abrupt changes in the temperature near the water-soil interface indicate exposure to surface water resulting from scour The Basic Principles of TSD are:

  5. In the Fall or Spring, the water temperature and the soil temperature are nearly equal at some point However, rainfall events usually generate flows where temperature in the channel changes Warmer temperatures in spring and cooler temperatures in the fall Potential Disadvantages of TSD:

  6. Development and Testing of Prototype Device • Thermocouples are mounted along the wall of a stainless steel tube • The spacing gives the temperature gradient along the tube • The device was first tested in the lab

  7. Data Acquisition System • A computer at the site captures the data from the thermocouples • A large steel box was used to hold and protect the computer system • The box was attached to the bridge

  8. Major Advantages of Digital System • Lower cost than analog systems • Easier to construct than analog systems • Develop software specific to the project • Data storage, transmission, and analysis are simplified

  9. Brass Tabs PVC Cap Electrically Conducting Epoxy DS 1920 DS 1920 iButton Capsule

  10. 1-WireTM Bus PVC Cap PVC Barb DS 1920 DS 1920 iButton Capsule

  11. 1-WireTM Bus Connection DS 1920 Sensor DS 1920 Thermal Probe

  12. DS 1920 Probe DS TINI 390 DS 2409 Switches Solar Power System High Power Cell Phone TSD System Architecture

  13. TSD System Architecture • TINI™ : Tiny InterNet Interface • The TINI™ board is Java™ computer • Web-enabled client • Low Cost (less $100) • Low Power

  14. Field Test Site Selection • A suitable site was selected just outside the City of Memphis • Telephone and power connections were available at the site • A large scour hole was evident downstream of the bridge

  15. Installation at Clear Creek Site • A pair of 50-ft. long steel piles were driven into the streambed to act as anchor points • The thermal probe was installed by jetting into the sandy soil • The device was bolted to the flange of the pile with clamps

  16. Installation at Clear Creek Site • Data cables are exposed to debris accumulation and failure • A pile extension was proposed to elevate the cable connection above the height of the surrounding channel banks

  17. Hand/foot pegs Cable shield Digital probe Installation at Clear Creek Site

  18. Field Data for March 1997

  19. Soil sensors before scour event After scour event Temperature sensors in air Scour Event - December, 1999

  20. TSD in New Bridge Construction

  21. TSD in New Bridge Construction

  22. Ground Wires DS 1920 Sensor Data Wires PVC End Cap DS 1920 Test Pile • A water-tight modular PVC pipe system was developed to protect the DS 1920 sensors inside the pile

  23. DS 1920 Test Pile • The PVC pipe system will allow for the DS 1920s to be easily arranged into a water-tight sensor array

  24. Future Development • We propose the development and installation of five additional sites in West Tennessee during the next year • We will monitor and maintain these sites • We will provide the data and the analysis of this data via the web • In addition, we will develop the capability to access the data at the site in real-time

  25. Clients Internet CentralScourServer Data BridgeInstrumentation and Client TSD System Architecture

  26. TSD System Summary • Modular and reusable • Adaptable to wide variety of scenarios • Provides easy access to data • Can incorporate analysis programs • Cost effective to develop and deploy

  27. Questions?

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