20 Years of Project Experience Using

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20 Years of Project Experience Using Ground
Penetrating Radar Presented to the Spring 2003
Midwest Concrete Consortium Meeting April 10,
2003 Chicago, IL
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GPR - Helping to Evaluate and Manage
Infrastructure Assets

• Pre-design input
• Post-Construction QC
• Process Improvement
• Performance Prediction

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What is Ground Penetrating Radar?

• Subsurface Interface Radar (SIR)
• Non-destructive testing technique
• Indirect methodology
• Measures material properties and material
  transitions
• Fast, accurate, reliable, and flexible
• Recognized, Accepted, Standards
• ASTM, AASHTO, SHRP, FWHA, USA COE, FAA, and
  State
• Complements, supplements other data and knowledge

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How Does GPR Work?

• Similar to airport radar and sonar/fish locator
• Focuses pulses of radar energy (radio waves) into
  the ground or structure
• Receives return reflections or echoes
• Generates a line of profile data beneath the
  antenna path

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GPR Trade-offs Limitations

• Select antennae (frequencies) for various target
  sizes and depths
• Depth vs Resolution (near-surface and thin-layer)
• Higher frequency near surface, thin layers, and
  small targets
• Lower frequencies deeper penetration, thick
  layers, and large targets
• Transmitting vs. Absorbing materials
• Radar friendly Dry, coarse-grained (sandy)
• Radar unfriendly Wet, fine-grained (clay)
• Metallic materials Complete reflectors
• Engineered materials (concrete, asphalt, bases,
  block, tile)
• Generally good transmitters, low absorbers
• Normally uniform - variations stand out
• May require limited calibration/confirmation
  cores (ground-truth)

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Earth Techs GPR Background

• In use since 1982
• Pioneered system configuration and use in civil
  engineering
• American Consulting Engineers Councils National
  Engineering Excellence Award in 1983
• Des Moines Airport Pavement Management Project
• First use of GPR and Deflection testing for
  pavement capacity analysis
• Projects in many service lines across the US and
  overseas
• Transportation - airports, pavements, bridges,
  route planning
• Mining, Geology - bedrock, overburden, ice
  thickness, karst/sinkhole
• Archaeology
• Site Investigations - UST, utility location,
  rebar location, burials

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Earth Techs GPR Project Locations
Projects in States Shaded Yellow
International Projects in Canada, Jamaica,
Japan, Korea, Okinawa, Saudi Arabia, and U.S.
Virgin Islands
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Pavement GPR ApplicationsHighways, Streets,
Airports, Parking Lots, Sidewalks, Slabs

• Verify/supplement/develop construction history
• Layer thickness
• Voids
• Reinforcing steel
• Durability cracking

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Pavement Project Construction History
Confirm records
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Pavement Project Layer Thickness
Variation-raw data (across runway)
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Pavement Project Layer Thickness
Variation-raw data (along runway)
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Pavement Project Layer Thickness

• FWD capacity analysis dependent on layer
  thickness
• Allowable Load
• Time to Failure

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Pavement Project Layer Thickness
Contract pay item based on cores/gpr
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Pavement Project Voids
Related to Utility Work Corner Breaks and
Shattered Slabs
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Pavement Project Voids
Related to Subsurface Water Movement
- Narrow Rills in Fine-Grained Soils - Circular
Slumps in Coarse Soils
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Pavement Project Voids
Related to Loading/Pumping Indicated by Faulting
and Fines
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Pavement Project Voids
Dual Antennae Data in wheelpaths - Weak pcc/base
signal - Strong echo at void - Note steel at
joints
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Pavement Project Steel Location

• Load-transfer dowels
• Rebar
• Wire mesh
• CRCP

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Pavement Project Steel Location
Pre or Post Grinding/Milling (depth of cover)
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Pavement Project Durability Cracks
Overlay - poor performance expectation
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Pavement Project Durability Cracks
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Bridge GPR Applications

• Voids under approach slabs
• Reinforcing steel location
• Bridge deck condition
• POTENTIAL concrete deterioration
• - Chloride
• - Moisture
• - Material segregation
• - Reinforcing steel corrosion
• Foundation/geologic
• Scour

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Bridge Approach Slab - Voiding
Extreme void condition
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Bridge - Reinforcing Steel
NH Standard - GPR as the ONLY tool to QC depth of
cover in new construction for contract pay item
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Bridge Deck Project - Deterioration
Digression INFRARED THERMOGRAPHY IS OUR PREFERRED
NDT TOOL FOR DETECTING CORROSION-INDUCED
DELAMINATION AND OTHER DECK DISTRESSES

• IR more closely aligned with physical breaks
• Full width coverage - no interpolation
• Faster data collection - less disruption
• Data used to develop deterioration models

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Bridge Deck Project - Deterioration
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Bridge Deck Project - GPR Waveforms
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Bridge Deck Project - Green Steel
Green Bar - desired concrete condition
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Bridge Deck Project - Corroded Steel
Corroded Black Bar - poor concrete condition
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Bridge Deck Project - Dual GPR Data Lines
Surface
Exp. Jt.
Deck Steel
Approach Slab Steel
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Bridge Deck Project - Planview Result
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Other GPR Applications

• Utility Location
• Underground Storage Tank
• Burials
• Archaeological surveys
• Mining/Bedrock
• Building/Structures

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Utility Location Project

• Shallower, small catch basin lead
• Deeper, large water main

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Pipe Location Project
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Burial/Cemetery Project

• Route planning r.o.w.
• Paupers grave
• Historic/prehistoric

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UST Project
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Archaeological Project

• New Seville, Jamaica
• Columbus landing site
• Integrated with aerial infrared
• GPR further focused excavation

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Mining Project
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Building/Structure Projects

• Electric Conduit/Data Lines Embedded in Slabs DO
  NOT DRILL
• World Trade Center, NYC Escalators
• Zoo Commissary Freezer Upgrade
• WWTP Control Panel Replacement

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Building/Structure Projects

• Structural Steel DO NOT DRILL
• Sports Dome Upgrade - braces for heavier
  replacement
• Rooftop Satellite Dish - mounting hardware
  drilled through roof and interior columns

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Building/Structure Projects

• Miscellaneous Subsurface Investigations Prior to
  Construction
• 80-Year Old Automobile Plant
• In-floor and sub-floor elements - must know
  before rehab design
• No surprises allowed during construction - done
  on annual shut-down week
• Ice Rink Snow Melt Pit Construction
• Avoid in-floor and sub-floor utilities
• Hospitals
• Morgue Floor
• X-Ray Equipment

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GPR Issues and Trends

• Research with Higher Frequencies - Hermes II
• Ultra Wide Band Regulations - FCC
• Antennae Arrays
• Enabled by improvements in computing
• Allow 3-D image output
• Contractor Models Now Available
• Use extreme care
• Periodic users, limited training
• Expertise/experience essential in all geophysical
  and indirect methods
• Continuing Research, Standards, Improvements

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Thank You!