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Fwd thinking
 

Fwd thinking

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    Fwd thinking Fwd thinking Document Transcript

    • Goals for this Session  What is an FWD?  Fundamentals of FWD operations and testing  Learn about some typical applications for an FWDDavid P. Orr, PE – Cornell Local Roads Program Pavement Deflection Isada, 1966 Benkelman beam 1
    • FWD Loading System KUAB DynatestCarl Bro JILS What Can a Typical FWD Measure?  Deflections  Load or Pressure  Temperature • Tow Vehicle • Data Acquisition System • Testing Device • Operator 2
    • 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 3
    • Travel to Site  Test Section LimitsTravel to SiteCoordinate Personnel Coordinate Personnel Traffic control crew  Sampling and geotechnical testing crew  FWD operator (as appropriate) 4
    • Inspect Test SectionInspect Test Section  General pavement condition  Pavement distressRecord Pavement  Prepare FWD for TestingTemperature? Who records?  Perform check of equipment  Prep for testing  Computer software Warm up FWD and  Check FWD Operation Collect Deflection Data 5
    • 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 dayTesting Program Perform Data Checks and Basic  An Effective Testing Program Should: Analysis   Minimize errors  Maximize data collection  Be flexiblePerform Data Checks and Basic Analysis  Prepare FWD for Travel Before or after leaving traveled way? What about the FWD software? Automation 6
    • 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 notesProvide Data to Engineer Data files Finish Analysis of FWD Data Other documentation PhotographsFinish 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 7
    • • 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 8
    • 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, SBCement Stabilization Demo After a Chip Seal• FWD Testing • Test pits are sited using FWD data Eden‐Evans Center Road – Eric County 9
    • 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 samplesLaboratory 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 11Gravel 50%Grey  2.6‐ 27‐ 40% A‐1‐a GP* NPSlag 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 10
    • Reconstruction or at least removal of the brown  • Visual inspectiongravel 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 CountyTesting 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 11
    • 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 25.0Bedrock 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) 12
    • 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 13