Detecting Bridge Scour by Thermal Variations Across the Stream Bed

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Detecting Bridge Scour by Thermal Variations
Across the Stream Bed

• July 19, 2000
• Presented by Paul L. Sharp

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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

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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

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The Basic Principles of TSD are

• 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

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Potential Disadvantages of TSD

• 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

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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

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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

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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

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DS 1920 iButton Capsule
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DS 1920 iButton Capsule
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DS 1920 Thermal Probe
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TSD System Architecture
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TSD System Architecture

• TINI Tiny InterNet Interface
• The TINI board is Java computer

• Web-enabled client
• Low Cost (less 100)
• Low Power

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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

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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

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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

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Installation at Clear Creek Site
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Field Data for March 1997
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Scour Event - December, 1999
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TSD in New Bridge Construction
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TSD in New Bridge Construction
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DS 1920 Test Pile

• A water-tight modular PVC pipe system was
  developed to protect the DS 1920 sensors inside
  the pile

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DS 1920 Test Pile

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

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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

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TSD System Architecture
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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

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Questions?