predicting rutting and fatigue cracking using the tsd
TRANSCRIPT
Motivation
Rutting Fatigue (alligator) cracking
Pavement distress
Pothole
Can be detected using profilers and surface imaging systems
BUT: Can only detect damage that has already occurred
Can we do better?
Motivation
Rutting- Compressive strains in subgrade- Shear strains in asphalt
What happens under a moving load?
Rutting Fatigue (alligator) cracking
Pavement distress
Pothole
Pavement distress
Strains in pavement
Mechanistic model
Pavement responseExternal load
Non-destructive pavement testing
Falling Weight Deflectometer
One issue: FWD is slow- Costly- Disrupts traffic- Safety hazard
Vertical strain
Fatigue (alligator) cracking- Tensile strains at bottom of asphalt layer
The Traffic Speed Deflectometer
- Measures at traffic speed 5 km/h – 80 km/h- Uses laser Doppler vibrometers to measure pavement response
- 𝑆𝐶𝐼300 is related to tensile strains in asphalt- 𝐷0 is related to compressive strains in subgrade- 𝐵𝐷𝐼 is related to strains in the base layer
Using TSD data
Simple indices:𝐷0, 𝑆𝐶𝐼300, 𝐵𝐷𝐼
Model fit / Numerical integration
Pavement distress
Back-calculation
Static analysis Compare
Pavement model Simulated slopes Measured slopes
Modify
FWD: Time-dependent experimentStatic deflectionTSD: moving load
Dynamic modeling
Inertia
Varying load 𝐹 = 𝐹(𝑥, 𝑡)
Visco-elasticity 𝐸 = 𝐸(𝑡)
• Investigated in frequency domain• Complex modulus 𝐸 𝜔 = 𝐸′ 𝜔 + 𝑖𝐸′′(𝜔)
Newton’s 2nd law for displacement
Asphalt complex modulus
Visco-elastic models
Well-described by the Huet-Sayegh model
Asphalt complex modulus
Granularmaterials
Damping ⇐
Hysteretic damping model
Time dependence: measurement examples
Road near Copenhagen.Three runs.
Large asymmetryDue to visco-elastic effects
Visco-elastic model fits
General finding: Measurements are well-described by the visco-elastic model
Relation to pavement distress
Pavement distress
Strains in pavement
Mechanistic model
Pavement responseExternal load
Back-calculation
Complex moduliStrains
Strains due to an actual driving truck!
Strains under driving truck
Related to compaction ruttingRelated to fatigue cracking
Related to shear flow rutting
Damage prediction
• Complicated physical mechanisms
• Empirical relations between strain and damage
• Typically:• damage ∝ 𝜖4
• N ∝ 𝜖−420 % difference in strains causes a factor 2 difference in N
Important to have good strain estimates
Summary
• Traffic Speed Deflectometer
• Visco-elastic back-calculation
• Strains under moving truck
TSD slopesSimulated slopes