Freight
The Influence of Multiple Axle Group Loads on Flexible Pavement Design
- Publication no: AP-R486-15
- ISBN: 978-1-925294-43-9
- Published: 15 June 2015
- PDF (free) Download
The current Austroads approach to assess the relative damaging effects of different axle groups on road pavements is by comparison of the peak static pavement deflection response under the axle groups. The assumption that deflection is the most appropriate indicator of pavement damage is open to question and is not consistent with the use of strains to calculate the performance of pavement materials.
In response, research conducted has determined that, with regard to the fatigue damage of asphalt and cemented materials, the standard load for an axle group type is dependent upon the thickness and modulus of the asphalt and the underlying pavement structure.
As a result, it is proposed that the mechanistic design procedure for flexible pavements not use the concept of standard loads, but rather that the procedure determines the pavement damage resulting from each axle load and each axle group within a traffic load distribution. An examination of the implications of pavement design outcomes in using this method determined that in general, reductions in both asphalt and cemented material thicknesses of up to 50 mm would result.
The research also determined that the currently used standard loads for tandem, triaxle and quad-axle were appropriate for use with the current empirical procedures for the design of granular pavements with thin bituminous surfacings.
- Summary
- 1. Introduction
- 1.1. The Australasian Pavement Network
- 1.2. Traffic Loads
- 1.3. Report Structure
- 1.4. Previous Related Reports
- 2. Australasian Practice
- 2.1. Overview of Pavement Design Methods
- 2.1.1. Design of Unbound Granular Pavements with Thin Surfacings
- 2.1.2. Mechanistic Design of Flexible Pavements
- 2.1.3. Rigid Pavement Design
- 2.2. Origins of Standard Axle Group Loads
- 2.3. Assumed Interaction between Axles
- 2.4. Limitations of Current Practice
- 3. Review of Alternative Methods
- 3.1. Introduction
- 3.2. 1993 AASHTO Guide
- 3.3. French Design Manual
- 3.4. Response to Load Methods
- 3.4.1. Relating Response to Damage
- 3.4.2. Maximum Response Methods
- 3.4.3. MEPDG
- 3.4.4. Multiple Peak Response Methods
- 3.4.5. South African Pavement Engineering Manual (2003)
- 3.4.6. Peak Mid-way Methods
- 3.4.7. Integration Methods
- 3.5. Summary
- 4. Review of Research
- 4.1. General
- 4.2. Asphalt Fatigue Using Simulated Multiple-axle Loads: Michigan State University
- 4.3. Effect of Different Wave Forms and Rest Periods on Fatigue: Chuo University Study
- 4.4. Effect of Different Wave Forms on Fatigue: French Studies
- 4.5. Effect of Different Wave Forms on Laboratory Fatigue: Homsi Study
- 4.6. Pavement Response to Multiple-axle Loads: BASt Study
- 4.7. Summary
- 5. Outline of Project Work
- 5.1. General
- 5.2. Rutting of Unbound Granular Pavements
- 5.3. Asphalt Fatigue
- 5.4. Cemented Materials Fatigue
- 5.5. Pavement Design Processes
- 6. Rutting of Unbound Granular Materials
- 6.1. General
- 6.2. Accelerated Loading Facility
- 6.2.1. Overview of ALF Prior to Modification
- 6.2.2. Multiple-axle Modifications
- 6.3. Site, Pavement Composition and Construction
- 6.3.1. Description of Site
- 6.3.2. Pavement Composition
- 6.3.3. Pavement Construction
- 6.4. Loading Applied During Testing Program
- 6.4.1. Loading Applied
- 6.4.2. Transverse Distribution
- 6.4.3. Line Marking
- 6.4.4. Pavement Bedding-in
- 6.5. Experiment Progression
- 6.6. Acquired Data
- 6.6.1. General
- 6.6.2. Loading Applied
- 6.6.3. Particle Size Distribution of Base Material
- 6.6.4. Density and Moisture Content of Base Material
- 6.6.5. Deformation of Imported Clay Subgrade Material
- 6.6.6. Deformation of the Surface of the Pavement
- 6.6.7. Pavement Deflection Testing
- 6.7. Preparation of Data for Analysis
- 6.7.1. Overall Deformation and Variation of Results
- 6.7.2. Variation in Deformation Performance
- 6.7.3. Measured In Situ Material Properties
- 6.7.4. Data to Reflect Pavement Properties
- 6.7.5. Measure of Performance
- 6.8. Analysis Using Generalised Model
- 6.9. Analyses Using Axle Group Pairing
- 6.9.1. General
- 6.9.2. 40 kN Single Axle and 80 kN Tandem Group
- 6.9.3. 60 kN Tandem Group and 80 kN Tandem Group
- 6.9.4. 60 kN Tandem Group and 90 kN Triaxle Group
- 6.9.5. 40 kN Single Axle and 90 kN Triaxle Group
- 6.10. Conclusions
- 7. Fatigue of Asphalt
- 7.1. Introduction
- 7.2. Response-to-load Model
- 7.2.1. Model Selection
- 7.2.2. FEM Mesh Generation
- 7.2.3. Analysis Parameters
- 7.2.4. Response Locations
- 7.3. 3D-FEM Response-to-load Analyses
- 7.4. Analysis of 3D-FEM Response-to-load Results Using Homsi’s Damage Model
- 7.4.1. Calculation of Homsi Parameters
- 7.4.2. Calculation of Relative Fatigue Damage
- 7.4.3. Calculation of Standard Axle Loads
- 7.4.4. Variations of Standard Axle Loads with Pavement Structure
- 7.5. Simplifying Homsi’s Model
- 7.6. Analysis of 3D-FEM Response-to-load Results Using Simplified Homsi Damage Model
- 7.7. Adjustment of Simplified Homsi Model for Use with Austroads Fatigue Relationship
- 7.7.1. Rearranging Simplified Homsi Model
- 7.7.2. Maximum Peak Model
- 7.8. Generalising Model to Consider Strains Generated by Each Axle
- 7.9. Analysis of 3D-FEM Response-to-load Results Using Summed Peaks Method
- 7.10. Selection of Damage Calculation Method
- 7.11. Damage Calculated Using Linear-elastic Response-to-load Model
- 7.12. Conclusions
- 8. Fatigue of Cemented Materials
- 8.1. General
- 8.2. Laboratory Flexural Test Methods
- 8.3. Sample Preparation
- 8.4. Laboratory Test Equipment
- 8.4.1. General
- 8.4.2. IPC Global Universal Testing System
- 8.4.3. IPC Global Test Control Software
- 8.4.4. Pulse Shape Generation
- 8.4.5. Control Software
- 8.5. Alterations to Test Procedures and Equipment
- 8.5.1. General
- 8.5.2. LVDT Frame Alterations
- 8.5.3. Test Geometry
- 8.5.4. Sample Size
- 8.5.5. Definition of Initial Modulus and Strain for Fatigue Testing
- 8.6. Data
- 8.6.1. Test Sequence
- 8.6.2. Flexural Modulus Data
- 8.6.3. Flexural Fatigue Data
- 8.7. Flexural Fatigue for Each Load Type
- 8.8. Analysis Using Estimated Strain Reach 100 000 Cycles of Loading
- 8.8.1. Background
- 8.8.2. Tolerable Strain
- 8.8.3. Correcting Tolerable Strains for Varying Density Condition
- 8.8.4. Effect of Load Shape on Tolerable Strain
- 8.9. Summary
- 9. Framework to Incorporate Multiple-axle Responses in Flexible Pavement Design
- 9.1. Empirical Design of Unbound Granular Pavements with Thin Bituminous Surfacing
- 9.2. Mechanistic Design of Bound Materials
- 9.2.1. Modelling Each Axle Group/Load Combination
- 9.2.2. Scaling Response-to-load Calculations for Different Load Levels
- 9.2.3. Excluding Superposition of Responses – Considering Isolated Axles
- 10. Determination of Characteristic Values of Parameters for multiple-axle group Modelling and Example Design Outcomes
- 10.1. Introduction
- 10.2. Design Traffic Distributions
- 10.3. Design Pavement Structures
- 10.4. Modelling Constituent Axles of Groups as Isolated Axles
- 10.5. Modelling of Combined Multiple-axle Groups
- 10.5.1. General
- 10.5.2. Axle Spacing
- 10.5.3. Effect of Superimposing Responses from Grouped Axles
- 10.5.4. Comparison of Scaled and Calculated Responses
- 10.5.5. Dynamic Load Considerations
- 10.5.6. Significance of Design Traffic Distribution
- 10.6. Summary
- 11. Conclusions
- 11.1. General
- 11.2. Empirical Design of Unbound Granular Pavements with Thin Bituminous Surfacings
- 11.3. Mechanistic Design of Bound Materials
- 11.4. Design Reliability
- References
- Appendix A Mean Deformation after Bedding-in: Tabulated
- Appendix B Mean Deformation after Bedding-in: Plotted
- Appendix C Pavement Deflection and Back-Calculated Moduli
- Appendix D Comparison of Deflection Data: Observed and Back-calculated
- Appendix E Method of Equivalent Thickness
- Appendix F Data Used in Load Pairing Analyses
- Appendix G Axle Loads in Multiple-axle Groups that Cause the Same Damage as a Standard Axle Determined from 3D-FEM Analyses and using Homsi’s Damage Model
- Appendix H Cemented Material Flexural modulus test results
- Appendix I Cemented Material Flexural Fatigue Test Results
- Appendix J Estimation of Tolerable Strain from Fatigue Test Results
- Appendix K Axle Group/load Distributions
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