1) The document discusses measuring pavement deflection variance at highway speeds using a method that simulates truck vibration responses based on road profiles measured with a laser profiler. 2) Precision testing showed reasonable repeatability and reproducibility, with standard deviations between runs of around 4%. 3) Comparisons with falling weight deflectometer measurements and ground penetrating radar indicated the method could accurately identify soft spots in the pavement correlated with increased vibrations and decreased structural integrity. 4) The study concluded that a "virtual tire footprint" sensor could better estimate the road profile perceived by the tire and identify soft spots compared to the laser profiler.

1. Measuring
Pavement Deflection Variance
at Highway Speeds
Photo: Scania Media Services
J Granlund, C A Lenngren, F Lindström
B Mårtensson
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

2. “Soft spots” can be amusing…
Video: Felicia Broberg, age 11
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

3. Presentation outline
• Soft spot measurement principle
• Accuracy: Reasonable precision, promising trueness
• Better profiling with virtual tire footprint road sensor
• Extremely uncomfortable seat vibration @ 30 km/h
• EU WBV action value exceeded @ all sites
• Road agencies should focus on WBV exposures, affecting
comfort and health
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

4. The soft spot measurement principle
Profilo- 3D Simulating Calculated
metry model truck ride response
Laser/inertial Profilograph Differences
= Soft spots?
Measuring real True truck
truck vibration response
Full loaded heavy truck
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

5. Objective of the work
Investigate trueness and precision
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

6. Precision: Repeatability
O 2183, Dals Ed - Nössemark
30 km/h
100%
90% 4.2 % standard
80%
deviation between 3
70%
60%
truck runs
Likeness
50%
40%
30%
20%
10%
0%
200 400 600 800 1000 1200 1400 1600 1800 2000
Distance [m]
Run 1 Run 2 Run 3
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

7. Precision: Reproducibility
AC 600, Östra Strömåker
30 km/h versus 50 km/h
100%
90% 3.7 % standard
80%
deviation between run
@ 30 km/h and
70%
60%
Likeness
50% @ 50 km/h
40%
30%
20%
10%
0%
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance[m]
30 km/h, springtime 50 km/h, springtime
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

8. Precision: Reproducibility
BD 374, Norr Storfors. 2 runs at 30 km/h
100%
4.8 % standard deviation
Simulated and measured wheel vibration likeness
90%
80% between spring and
70% autumn run
60% Lower likeness during
50% spring. Softer pavement
40% due to thaw?
30%
20%
10%
0%
400 900 1400 1900 2400 2900 3400
Distance [m]
Spring Autumn
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

9. Trueness - Falling Weight Deflectometer
AC 600, Östra Strömåker
1000 100%
90%
80%
Truck wheel vibration likeness
70%
60%
Log E u [MPa]
100 50%
40%
30%
20%
10%
10 0%
7250 7450 7650 7850 8050 8250
Distance [m]
Eu min, springtime Wheel vibration likeness
Soft subgrade with Eu down to 24 MPa @ indicated soft spots
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

10. Trueness - Ground Penetrating Radar
Poor pavement integrity @ soft spots, due to frost fatigue
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

11. Virtual tire footprint sensor
Tires are 200 – 400 mm wide. The laser beam is < 1 mm wide.
The virtual tire footprint (VTF) sensor covers 300 mm width.
90%
The VTF sensor
estimates the tire
perceived road profile 85% Average vibration likeness over 6 km
85.3%
83.6%
much better.
80% 79.1%
77.4%
74.7% 74.5% 74.5%
75%
70%
Tire footprint Laser 12 Laser 13 Laser 14 Laser 15 Laser 16 Tire footprint
sensor A sensor B
Longitudinal profile recorded by different sensors
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

12. Seat vibration @ 30 km/h
Worser ride at road with lower IRI
2,5 6
5,50 2,31
2,24
5 ISO 2631-1(1997):
2
RMS of weighted vibration
4,34
1,70 4,13 ”Extremely
3,95
acceleration [m/s 2]
4
uncomfortable” = 2 m/s2
1,5
IRI [mm/m]
1,14 3
1
0,85
0,73 0,74 2
0,56 2002/44/EC:
0,5
1
Action Value A(8)
= 0,5 m/s2
0 0
O 2183 O 1996 AC 600 BD 374
Test site
Average vib level Max transient 1 s vib value IRI 20 m average value
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

13. Conclusions
• Reasonable precision
• Promising trueness
• Successful virtual tire footprint sensor for road profiling
• Extremely uncomfortable seat vibration @ 30 km/h
• EU WBV action value exceeded @ all sites
• Road with lower IRI was much more uncomfortable
• Road agencies should focus on WBV exposures, affecting
comfort and health
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

14. Acknowledgements
• Nordic Road Association
• Swedish Road Administration
• Axiom EduTech AB
• Malå GeoScience and Radar Väg Analys AB
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway

15. Comfort, comfort my people, says your God.
A voice of one calling in the desert;
-Prepare the way for the Lord, make straight paths for him.
Every valley shall be filled in, every mountain and hill made low.
The crooked roads shall become straight, the rough ways
smooth.
The path of the righteous is level;
O upright One, you make the way of the righteous smooth.
And all mankind will see God's salvation.
Isaiah 26:7 Isaiah 40:1,3-5 Luke 3:5
7'th Int Conf on Bearing Capacity of Roads, Railways and Airfields, 2005, Trondheim, Norway