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Insert the title of yourpresentation here
Presented by Name Here
Job Title - Date
Different loads and load pulses
make comparisons between LWD,
FWD, HWD and SHWD difficult
Brian Ferne and Peter LangdaleTRL 10 June 2010
EUROFWD10
(6th
European FWD Users Group Meeting)
BRRC, Brussels10 and 11 June 2010,
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Insert the title of yourpresentation here
Presented by Name Here
Job Title - Date
or Harmonising FWDs?
Brian Ferne and Peter LangdaleTRL 10 June 2010
EUROFWD10
(6th
European FWD Users Group Meeting)
BRRC, Brussels10 and 11 June 2010,
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Page 3
Table of contents
A short history of harmonisation
Introduction to FWDs, L(F)WDs, H(F)WDs and SH(F)WDs
History of harmonisation
Crow/COST336
UK HA correlation trials
1
23
4
5
LWD use and comparisons
HWD use and comparisons
Summary and questions to be answered
6
7
8
USA SHRP procedure
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History of measurement
Pulse loads
- 1963 Bretonniere France
- 1964 Finsen/Ullidtz/Gautier Denmark
- 1966 Isada USA
- 1968? First Phoenix FWD, Denmark
- 1968? First Dynatest FWD, Denmark- 1976 First KUAB FWD, Sweden
- 1987 First JILS FWD, USA
- 19?? First Komatsu FWD, Japan
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What is an FWD? (1)
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d1
d5
d3
d4
d2
d6 d7
Applied load
Falling Weight Deflectometer Schematic
Geophones
Deflection bowl
Loading plate
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Types of FWD
FWD (Falling Weight Deflectometer)Peak load = 25 to 100 kN
HWD (Heavy Weight Deflectometer)
Peak load = 50 to 250 kN
LWD (Light Weight Deflectometer)
Peak load = 1 to 10 kN
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How do we use FWDs onpavements?
To assess the structural properties of
New pavements
In-service pavements
Rehabilitated pavements
Structural properties can include layer stiffnesses and loadtransfer at joints or cracks
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Therefore :
Vital that:
Measurement
InterpretationIs
Accurate
Consistent
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Therefore :
Vital that:
Measurement
InterpretationIs
Accurate ?
Consistent
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First overall assessment
1989
Comparison of Falling Weight Deflectometer systems available inthe United Kingdom
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Four Survey Contractors
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QuestionHow should we test our FWDs?
Main Options:
USA SHRP-LTPP
- emphasis on calibration of
components
Dutch CROW protocol- emphasis on correlation of
whole systems
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Main Options:
USA SHRP-LTPP
Dutch CROW protocol
QuestionHow should we test our FWDs?
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Main Options:
USA SHRP-LTPP
Dutch CROW protocol
Preliminary trial held in November 1998 sponsored by
the Highways Agency with support from the UK andIreland FWD Group
QuestionHow should we test our FWDs?
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Six machines from five companiesSix machines from five companies
-- FiveFive FWDsFWDs, one HWD (all, one HWD (all DynatestDynatest))
All machines similarly configuredAll machines similarly configured
(Load, geophones, plate size, 5 drops, smoothing)(Load, geophones, plate size, 5 drops, smoothing) Machines inspectedMachines inspected
modelmodel
weight and buffer configurationweight and buffer configuration plate typeplate type
load attainment methodload attainment method
geophone locationsgeophone locations
calibration detailscalibration details
PreliminaryPreliminary
1998 FWD1998 FWD
Correlation TrialCorrelation Trial
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How do we use the results?
Pass/fail criteria
FCF (mean) >0.95 and 0.90 and
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Trial Development
1998 - preliminary trial (6 machines)
1999 - second trial (also looked at rigid pavements,mid slab and joints)
(7 machines)
2000 - First mandatory trial!
(9 machines)
2000 First mini trial
Now annual exercise with 16 machines in 2005
20 machines in 2010
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HA requirements for measurement
All machines operating on trunk road network must:
Take part in and pass annual correlation trial
Be retested following any major maintenance
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FWD Correlation 2009 - FCF
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FWD and LWD test equipment
Comparison of foundation stiffness
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Comparison of foundation stiffnessmeasurements by LWD and FWD
Repeatability of FWD : Low stiffness foundation
1
10
100
1000
10000
0 50 100 150 200 250 300 350
Foundationstiffn
ess(MPa)
PRIMA FWD
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LWD and FWD test methods
Is the relationship between an LWD and a
FWD dependent on the foundation typetested?
Comparison of LWD and FWD on an
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Comparison of LWD and FWD on anunbound granular foundation
0
100
200
300
400
0 50 100 150 200 250 300Surface stress (kPa)
Surfacemo
dulus(MPa
PRIMA FWD
Comparison of LWD and FWD on a
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Comparison of LWD and FWD on abound foundation
0
100
200
300
400
0 100 200 300 400 500Surface stress (kPa)
SurfaceModulus(MP
a)
PRIMA FWD
Comparison of LWD and FWD on
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Comparison of LWD and FWD onunbound and bound foundations
Foundation stiffness (MPa) by:Foundation
typeLWD FWD
Proportionaldifference*
(%)
167 210 -20
204 244 -16
110 138 -21
98 115 -15
Unbound
38 78 -53Weakly bound 89 108 -18
335 321 5Bound
1055 1125 -6
*{(LWD-FWD)*100 / FWD}
Potential LWD/FWD adjustment and
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Potential LWD/FWD adjustment andtest procedure
Test Demonstration Area with LWD and FWD
Calculate factor to adjust LWD test results
Confirm precision of calibration is adequate
Use LWD on Main Works with results adjustedby factor.
Compare running mean averages of 5 testresults and individual values with targetstiffness values
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Two questions were posed:
-Is it essential to use a Heavy WeightDeflectometer when assessing airfields?
-How should we interpret the results from
FWD/HWD?
FWD HWD C i
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FWD - HWD Comparison
The study:
FWD (TRL) and HWD (Dynatest UK)
Simultaneous testing Range of airfields and constructions
Load transfer testing (joints)
Stiffness testing (mid-slab)
Effect of load
Effect of plate size
FWDFWD HWD C iHWD C i R lt ( idR lt ( id l b)l b)
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FWDFWD -- HWD ComparisonHWD ComparisonResults (midResults (mid--slab)slab)
Scampton Slab B6 Central Deflections (D1)
0
100
200
300
0 50 100 150 200 250 300
Load (kN)
Deflection(microns)
FWD 300mm plate
FWD 450mm plate
HWD 300mm plate
HWD 450mm plate
FWDFWD HWD ComparisonHWD Comparison Results (midResults (mid slab)slab)
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FWDFWD -- HWD ComparisonHWD ComparisonResults (midResults (mid--slab)slab)
Marham Slab E1 Cent ral Def lectio ns (D1)
0
100
200
300
400
0 50 100 150 200 250 300
Load (k N)
De
flection(m
icrons)
FWD 300mm plateFWD 450mm plate
HWD 300mm plate
HWD 450mm plate
FWDFWD HWD ComparisonHWD Comparison Results (midResults (mid slab)slab)
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FWDFWD -- HWD ComparisonHWD ComparisonResults (midResults (mid--slab)slab)
Cottesmore Slab G1 Central Deflections (D1)
0
100
200
300
400
0 50 100 150 200 250 300
Load (kN)
Deflection(microns)
FWD 300mm plate
FWD 450mm plate
HWD 300mm plate
HWD 450mm plate
FWD HWD Comparison Conclusions
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No systematic differences between the FWDand HWD test results
Generally good agreement in the mid-slab
results between test machines and platesizes
However more recent work has suggestedthat there can be significant differences oncertain airfield pavement constructions
FWD - HWD Comparison Conclusions
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Introduction of Super Heavyweight FWD - SHWD
Page 36
Alternative calibration approach?
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(1)
Use independent deflectionmeasure e.g.accelerometer?
C o m p a r i so n o f F WD a n d A c c e l e r o m e t e r : 3 0 0 m m o f f
-100
-50
0
50
100
150
200
250
51.41 51.42 51. 43 51.44 51. 45 51.46 51. 47 51.48 51.49
t i m e ( s e c s )
Ac cel er ometer
FWD
-200
-150
-100
-50
0
50
100
150
200
250
300
0 10 20 30 40 50 60
Time [s]
Deflection[m]
Alternative calibration approach? (2)
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Alternative calibration approach? (2)
But an accelerometer confirms just the response of partof the system the deflection measuring part
What about the correctness of the loading system?
For rolling wheel loading, pavement response dependson load configuration and speed the load configurationis can be defined fairly easily but will the response of thetyres remain the same over time?
For FWD impulse loading the response also depends onthese parameters what is the correct loading pulse?
how well defined is this?
Varying load pulse on one FWD
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Varying load pulse on one FWD
-100
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60
Time (s)
Pressure(kPa)
Test 1
Test 2
Test 3
Test4
-100
-50
0
50
100
150
200
250
300
0 20 40 60 80
Time (s)
Deflection
@D
1
Test 1_d1
Test 2_d1
Test 3_d1
Test4_d1
FWD pulse with different durations
Deflection response at Geophone 1
FEM modelling of FWD pulse
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FEM modelling of FWD pulse
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 0.01 0.02 0.03 0.04
Time (s)
Normalisedpulse
-0.00001
-0.000005
0
0.000005
0.00001
0.000015
0.00002
0.000025
0.00003
0 0.02 0.04 0.06 0.08
Time (s)
Verticaldeflection(m)
Pulse 0
Pulse 1
Pulse 2
Normalised pulse shapes used in
some Finite Element analyses
Effect of FWD pulse on the vertical
deflection under the centre of the
plate
Extracts from :Staring at Deflection Traces: Lookingor the Truth in Time Histories by David P Orr
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or the Truth in Time Histories by David P Orr,Cornell LRP
-700
-600
-500
-400
-300
-200
-100
0
100
200
0 10 20 30 40 50 60
Time (mSec)
Deflection
(m
icrons)
-400
-300
-200
-100
0
100
200
300
400
500
600
0 10 20 30 40 50
Time (mSec)
Deflection(
m
ic
rons)
-300
-200
-100
0
100
200
300
0 20 40 60 80 100 120
Time (mSec)
Deflection(
microns)
-150
-100
-50
0
50
100
150
200
250
0 20 40 60 80 100 120
Time (mSec)
Deflection
(mic
rons)
Brand Average Rise Time
(mSec)
Carl Bro 13.2
Dynatest 13.1
JILS 18.4
KUAB 14.5
Alternative calibration approach? (3)
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Alternative calibration approach? (3)
Could we compare/calibrate all deflection measuringdevices with the deflection response under a standardaxle at traffic speed?
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Some questions for discussion? (1)
Page 43
Can we define a specification for a standard FWD for each main
purpose?
Is calibration of the individual components adequate or do we needto check the whole system?
If we use the fleet mean as the reference, how many machinesand of what type are needed?
If so, how do we prevent a steady change in the mean of the
fleet?
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Some questions for discussion? (2)
Page 44
Since, ultimately, we are using FWD measurements to predict thestructural condition of the pavement, and its response to rolling wheelloads:
Should we therefore also be referencing all measurements topavement responses under a standardised rolling wheel load?
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Page 45
Thank you!
Presented by Brian Ferne 10 June 2010Tel: +44-1344-770668Email: [email protected]
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