Mechanistic Pavement Design A Road to Enhanced Understanding of Pavement Performance Sigurdur Erlingsson Dept. of Civil and Env. Engineering University of Iceland Iceland & Dept. of Highway Engineering VTI Sweden Seminar on Pavement Design System and Pavement Performance Models Reykjavik, 22.–23. March, 2007
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Mechanistic Pavement DesignA Road to Enhanced Understanding of Pavement Performance
Sigurdur ErlingssonDept. of Civil and Env. EngineeringUniversity of IcelandIceland&Dept. of Highway EngineeringVTISweden
Seminar on Pavement Design System and Pavement Performance ModelsReykjavik, 22.–23. March, 2007
Outline
• The Problem• Current Design Methods• Mechanistic-Empirical Design Methods• Important Factors Influencing Pavement Performance
– Traffic Loading– Material Characteristics– The Climatic Conditions and Seasonal Variation of Pavement Response
• Response Calculation and Distress Prediction• Validation
– Accelerated Testing of Pavement Structure
• Conclusion
The Problem Distress Mechanisms
Longitudinal Longitudinal CrackingCracking
RoughnessRoughness
Thermal CrackingThermal Cracking
RuttingRutting
Fatigue Fatigue CrackingCracking
Current Design Methods
• Relay on empirical correlations with past performance.• Based on 1950´s AASHTO Road Test data.• Index value based characterization
– R-value– CBR-value
• They are obscure and difficult to apply in new situations.
Load 50 kN, φ
= 300 mm
Asphalt
Unbound or BoundBase
Subbase
Subgrade
1. Tensile strain at pavement surface.2. Tensile strain at bottom asphalt.3. Compressive stresses in top unbound base.4.Tensile strain at bottom bound base5. Vertical compressive strain at top subbase.
6. Vertical compressive strain at top subgrade.
CriticalCritical stress and stress and strainstrain locationslocations
UseUse linearlinear elasticelastic multimulti layerlayer system, system, soso characterisecharacterise materialsmaterials withwith E and E and μμ..AssumeAssume full full adhesionadhesion betweenbetween the the layerslayers..UseUse static static loadload(s).(s).UseUse transfer transfer functionsfunctions ((fatiguefatigue relations) to relations) to calculatecalculate pavementpavement lifelife..Drawbacks: Drawbacks: materialsmaterials are NOT are NOT linearlinear elasticelastic. . TheyThey are non are non linearlinear elastoelasto--viscovisco-- plasticplastic and and oftenoften raterate, , temperaturetemperature and and moisturemoisture dependentdependent..
Mechanistic-Empirical Design
•• MechanisticallyMechanistically calculate pavement response (i.e., stresses, strains, and deflections) due to:– Traffic loading– Environmental conditions
• Accumulate damagedamage over time–– EmpiricallyEmpirically relate damage over time to pavement distresses,
e.g.:CrackingRuttingFaulting
•• CalibrateCalibrate (validation) predictions to observed field performance
Mechanistic-Empirical Design
Climate TrafficMaterials
Structure
DistressResponse
Time
Damage
Damage Accumulation
Incremental design procedure – Flow diagram
1. Initial Condition and Structure
2. Geometry
4. Material Properties
6. Response Model
10. Current Condition Σ(ΔD)
5. Climate and Enviroment
7. Stresses, Strains,Displacements
9. Structural Change ΔD
8. Performance Model
i = 0t = 0
11. History of Pavement Damage
i = i+1ti+1 = ti +Δt
3. Traffic and Loads
Design criteria -
Factors Influencing Performance and Distress Development
• Traffic Loading• Material Characteristics• Climatic Conditions and Seasonal Variation of Material
To increase the understanding of pavements performance under heavy loading conditions.
Heavy Vehicle Simulator
The Pavement Structures (IS02 & IS03)
Surface dressing, 2 layers, 12-16/8-12 mm crushed aggregate
230
430
z [mm]
Subbase, 0-75 mm aggregate
Subgrade, sand
Unbound base, 0-25 mm crushed aggregate
030
Surface dressing, 2 layers, 12-16/8-12 mm crushed aggregate, 30 mm
230
430
z [mm]
Subbase course, 0-75 mm aggregate
Subgrade, sand
Unbound base, 0-25 mm crushed aggregate
030
Bitumen stabilized base, 0-25 mm crushed aggregate
130
IS 02 IS 03
Response Testing - Numerical Simulations
• 2-D Axi & 3-D analysis.
• MLET & FEM analyses
• Linear and non-linear base behaviour
• Distress prediction
IS02 – Single wheel, p = 800 kPa FEM: Vertical displacement
IS02 Vertical Stresses vs. Depth
Depth [cm]
0.0
Surface dressing
Unbound base course
Subbase
Subgrade
1.2
20.3
39.7
Single wheel Dual wheel
Profile 1 Profile 2 Profile 3
W = 120 kN 0
10
20
30
40
50
0 200 400 600 800 1000Stress σz [kPa]
Dep
th [c
m]
Measurements3D FEM LE2D Axi MLET LE2D Axi MLET NLE2D Axi FE LA2D Axi FE NLE
p = 900 kPa
Conclusions
• Mechanistic - empirical based design methods are under development in many countries and will therefore probably be in use in the near future. To be able to use such methods we need to obtain information for modelling purposes on factors affecting pavement performances, such as– Axle loading – Material properties – Weather and environmental conditions
• Further we need information to calibrate and validate such methods if acceptable agreement between real performance and our estimation is to be achieved.
Conclusions cont.
• What will we gain– Far more realistic pavement characterization– Better understanding of pavement performances– Effects of new loading conditions such as increased loads,
higher tyre pressure and multiple axle, can easily be estimated
– Future enhanced or improved knowledge can be easily implemented