The document discusses an overview of falling weight deflectometer (FWD) testing. It describes what an FWD can measure, including deflections, load, and temperature. It outlines the typical components of an FWD system and provides details on FWD testing protocols such as coordinating personnel, collecting deflection data, and analyzing results. Finally, it lists some common applications of FWD testing for flexible and rigid pavements including design, rehabilitation, and network evaluation.

1. Goals for this Session
 What is an FWD?
 Fundamentals of FWD operations and testing
 Learn about some typical applications for an FWD
David P. Orr, PE – Cornell Local Roads Program
Pavement Deflection
Isada, 1966
Benkelman beam
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2. FWD Loading System
KUAB Dynatest
Carl Bro JILS
What Can a Typical FWD Measure?
 Deflections
 Load or Pressure
 Temperature
• Tow Vehicle
• Data Acquisition System
• Testing Device
• Operator
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3. FWD with GPS
• Deflections
• Load or Pressure
• Temperature
• (Surface and Air)
‐Dwight D. Eisenhower
FWD Testing Protocol
 Travel to site
 Coordinate personnel
 Inspect test section
 Record temperature & other measurements
 Prepare FWD for testing
 Warm up FWD & check FWD operation
 Collect FWD data
 Perform data checks & basic analysis
 Prepare FWD for travel
 Return to base
 Provide data to engineer
 Finish analysis of FWD data
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4. Travel to Site
 Test Section Limits
Travel to Site
Coordinate Personnel Coordinate Personnel
 Traffic control crew  Sampling and geotechnical testing crew
 FWD operator (as appropriate)
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5. Inspect Test Section
Inspect Test Section  General pavement condition
 Pavement distress
Record Pavement
Prepare FWD for Testing
Temperature?
 Who records?  Perform check of equipment
 Prep for testing
 Computer software
Warm up FWD and
Check FWD Operation
Collect Deflection Data
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6. Testing Considerations Collect Deflection Data
 Type of FWD Testing  Test spacing
 Research Level  Number of drops per point
 Project Level
 Number of load levels
 Network Level
 Type of Pavement Structure  Project Level FWD Testing
 Flexible  Spacing 25‐100 ft
 Rigid (Jointed or Continuously Reinforced)  Network Level FWD Testing
 Composite  250‐500 ft spacing
 Other
(aggregate, surface treatment on aggregate, etc.)  Maximize use of traffic control
 Determine average test points per day
Testing Program Perform Data Checks and Basic
 An Effective Testing Program Should: Analysis
 Minimize errors
 Maximize data collection
 Be flexible
Perform Data Checks and Basic
Analysis Prepare FWD for Travel
 Before or after leaving traveled way?
 What about the FWD software?
 Automation
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7. Prepare FWD for Travel Return to Base
 Prepare for high‐speed travel  Missing data will always be missing
 Create backup of data
 Complete hand written notes
Provide Data to Engineer
 Data files Finish Analysis of FWD Data
 Other documentation
 Photographs
Finish Analysis of FWD Data
 Is the FWD data good?
 Data checks in the field
 What is the goal of the testing?
• The testing company, the engineer,
and the County working in collaboration
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8. • Geotechnical investigation • NO!
• Test pits • Depends upon data needs
• Core holes and length of section
• GPR? • Take advantage of a full day of testing
• Pavement temperature
• Pictures
• Distress investigation
• ….
Typical Applications of an FWD
 Flexible Pavements
 Design of rehab/overlay
 Subgrade response
 Identify weak areas
 Forensics
 Rigid Pavements
 Layer moduli
 Subgrade support
 Locate bad joints or voids
 Network Evaluation
 Pavement parameters
 Subgrade strength
Landon Road
 Where does the poor base area begin and end?
 What are the best locations for the test pits?
 Will cement stabilization work?
 Did the rehab work?
Landon Road
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9. Testing Program Plots of FWD Deflection
Dropt Height 4 Deflections
 Visual inspection 80 Center Deflection
70
 Interview with Town Highway Superintendent 60
50
Deflection (mils)
 FWD testing in Outer Wheel Path 40
30
20
 2 test pits 10
0
 Soil samples 0 1000 2000
April 02, NB
3000
Station (feet)
4000
Sept 02, SB
5000 6000
Dropt Height 4 Deflections
Outer Deflection 72"
3
2.5
2
Deflection (mils)
1.5
1
0.5
0
0 1000 2000 3000 4000 5000 6000
Station (feet)
April 02, NB Sept 02, SB
Cement Stabilization Demo After a Chip Seal
• FWD Testing
• Test pits are sited using FWD data Eden‐Evans Center Road – Eric County
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10. Eden‐Evans Center Road Testing Program
 Why does the road heave so badly?  Visual inspection
 What are the rehabilitation options?  Interview with crew leaders
 FWD testing in Outer Wheel Path
 2 test pits
 Soil samples
Laboratory Tests Brown Gravel
Sieve Test - Upper Brown Gravel - Test Pit 1
Erie County - Eden-Evans Center Road
100%
90%
80%
Material AASHTO Unified % Fines PI SE
Percent Pasing
70%
Brown 60%
A‐2‐4 GM‐GC 30.6% 7 11
Gravel 50%
Grey 2.6‐ 27‐ 40%
A‐1‐a GP* NP
Slag 6.5% 29 30%
20%
Subgrade A‐4 SM‐SC 44.1% 6 13 10%
0%
0.001 0.01 0.1 1 10
Cornell Local Roads Program Grain size (inches)
Variation in Deflection Data Rehabilitation Choices
 Overlay
 Reconstruction
 Recycling the Surface
 Full Depth Rehabilitation
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11. Reconstruction or at least removal of the brown • Visual inspection
gravel is a minimum needed at this site • Test pits
• Laboratory analysis
County Rt 5
 How good was the construction in 2011?
 Are there any weak spots?
 What is the expected lifespan?
County Route 5, Lyme, NY – Jefferson County
Testing Program Bedrock at Station 1+50
 Visual inspection Can see exposed bedrock
 Discussion with County
 Road is also in Seasonal Research Study ~6 feet deep
 FWD testing in Outer Wheel Path
 Use data from research geotechnical investigation
 Soil samples
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12. Bedrock Depth
Bedrock at Station 2+80 (from FWD data)
Distance (feet)
9.9 feet deep 0 100 200 300 400 500
0.0
Bedrock Depth (feet)
5.0
10.0
15.0
20.0
25.0
Bedrock Depth
(from FWD data)
Backcalculation Model
Distance (feet) Layer Thickness (inches)
0 2,000 4,000 6,000 8,000 AC 7.5
0
Gravel 11.0
Bedrock Depth (feet)
5
10 Upper Subgrade 24
15
20 Lower Subgrade Calculated
25
Bedrock ∞
Weak Spots Terminal ESALs
Lower Subgrade Modulus 4.E+09
120,000
3.E+09
Modulus (psi)
100,000
ESALs
80,000 2.E+09
60,000
40,000 1.E+09
20,000
0 0.E+00
0 2,000 4,000 6,000 8,000 0 2,000 4,000 6,000 8,000
Distance (feet) Distance (feet)
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13. Terminal ESALs
100,000,000
80,000,000
• Bedrock (within ~25 feet)
ESALs
60,000,000
• Weak spots (only a relative value)
40,000,000
5,000
20,000,000 AADT • Can also be used with thickness information to
0 determine the strength of the pavement
0 2,000 4,000 6,000 8,000
Distance (feet)
Conclusions
Non destructive testing device
 Lots of data quickly
 Not always the right choice • An FWD is a non‐destructive testing (NDT) device
 Backcalculation? for pavement that ‘simulates’ the loading of a
truck traveling at about 40 mph
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