pavement deflection measurements using the...
TRANSCRIPT
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Pavement Deflection Measurements Using the Geobeam
Steven Anderson
Auckland Regional Manager
Geotechnics Ltd.
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The Geobeam
• The Geobeam is an
instrumented
Benkelman Beam
• Developed in the late
1980’s by Tonkin &
Taylor
• Measures deflection
bowls
• Slow static test
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The Geobeam
• Cantilevered and an inductive
transducer - eliminate friction affects
Transducer
Geobeam
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Upgraded Geobeam
• New wireless technology
Before 2005 After 2007
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• Fifth wheel with rotary encoder
• Measures a deflection for every ~10mm of
travel
Upgraded Geobeam
Fifth Wheel
Distance Measurement
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Field Program - Data Capture
• Data capture shows real time deflection bowls
Capture Software
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Geobeam Report Processor
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Geobeam Report
Verbose Raw Data
Smoothed Data
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Geobeam Report
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2.694m 1.410m
4.104m
dbowl
d
Deflection, d0
1. Without Bowl Correction
(Where (s-i) and (s-f) differ by less than 0.03mm)
d0 = ( s-f )
s = start reading at maximum deflection 0m (mm)
i = intermediate reading at 2.694m (mm)
f = final reading at ≥10m (mm)
2. With Bowl Correction
(Where (s-i) and (s-f) differ by more than 0.03mm)
d0 = (s-f) + 4.104 ( i-f ) = (s-f) + 2.91( i-f )
1.410
NOTE – Assumes rear foot is not in the bowl
s i f
d0
Calculation of Pavement Deflection, d0
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Calculation of Bowl Radius and Curvature Function
Load
P
Distance, LL = 0.2m
Curvature Function, CF
CF = d0-d200
Bowl Radius, R
R2 = {R-(d0– dL)}2+L2
R = L 2
2(d0-dL)
R = L2
2δ
When L = 0.2m
R = 0.04
2δ
d0 dL
R
L
δ
R
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Calibration of Equipment
Calibration Average Data
-6.00000
-5.00000
-4.00000
-3.00000
-2.00000
-1.00000
0.00000
1.00000
2.00000
3.00000
4.00000
0.00 2.00 4.00 6.00 8.00 10.00
Micrometer (mm)
Defl
ecti
on
Un
it (
V)
60mm D 6mm T Puck Offset 10mm
60mm D 6mm T Puck Offset Nil
60mm D 6mm T Perspex Offset Nil
60mm D 6mm T None Offset Nil
40mm D 10mm T Puck Offset 20mm
40mm D 10mm T Puck Offset 10mm
40mm D 10mm T Puck Offset Nil
40mm D 6mm T Perspex Offset 20mm
40mm D 6mm T Perspex Offset Nil
40mm D 6mm T None Offset Nil
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Correlation with Benkleman Beam
Geobeam vs Benkelman
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
Chainage
De
fle
cti
on
mm
Geobeam
Benkelman Beam
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More Information
More data means more information
Excellent deflection bowls
Real time bowls indicate test problems
Accurate determination of curvature function
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Where to from here?
More development
• More field work to bullet proof the electronic
system
• More validation, correlation and calibration
Interesting projects
• Consolidation effect in pavements
• Measuring subgrade and basecourse bowls
at the same time