1. Considering multiple-axle group loads in mechanistic design of bound pavements Michael Moffatt

2. Source: Department of Planning, Transport and Infrastructure, South Australia

4. 80 kN Standard Axle equivalent Standard Axle Repetitions

5. Axle type Standard group load [kN] single axle – single tyres53 single axle – dual tyres80 tandem – dual tyres135 triaxle – dual tyres181 quad-axle – dual tyres221 Failure mechanismLDE asphalt fatigue5 cemented material fatigue12 total deformation7

6. Assumptions

8. Fatigue testing flexural fatigue testing using trapezoidal beam displacement control during testing no rest periods simulated axles had equal peaks 8

9. Simplified Homsi model

10. non-linear elastic support materials localised stress/modulus states superpositioning of responses 3D FEM

11. Asphalt Crushed rock Subgrade Pavement structures 1000 MPa 3000 MPa 5000 MPa High quality crushed rock Lower subbase Highly plastic clay (CBR 3%) Sand (CBR 15%) 50 100 200 300 mm 200 400 600 mm

15. Fatigue models Austroads Simplified Homsi Maximum peaks

18. Damage models Summed peaks Maximum peaks

20. Layered linear-elastic analyses similar

21. Equating damage by strain (+ superposition) varies with pavement structure thicknesses modulus Single load equivalency values unsuitable Model traffic spectrum, and assign damage to each combination of axle group and load same as for concrete design Implementation in the guide

22. Design process Austroads traffic load distribution + HVAG count SAR5 Model candidate structure with Standard Axle Allowable loading cf. SAR5 Summed peaks traffic load distribution + HVAG count Model candidate structure with axle types/loads in TDL Sum damage (want ≤ 100 %) Austroads Summed peaks

24. Cemented materials fatigue

27. conclude that relative damage is the same as number of axles in group same procedure as for asphalt Findings Group damage relative to single axle GroupsRelative damage 22.4 32.8 4.1

28. Design example 1 x 10 8 HVAG

29. Asphalt Crushed rock Subgrade Candidate structure 3000 MPa CBR 7 % 340 mm 300 mm

31. Reference load: 53 kN XXYY 60.354.4

34. Reference load: 135 kN XXYY 58.243.0 XXYY 60.744.2 XXYY 58.243.0 XXYY 60.744.2

39. Further information Seek me out today. 26 th ARRB Conference paper. www.arrb.com.au/ARRB-Conferences Research Report for Austroads in press. PhD thesis in pre-pre-press. Thank you www.arrb.com.au