28 pavement design

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  • 1. 1 Pavement Design CE 453 Lecture 28

2. 2 Objectives Understand and complete ESAL calculation Know variables involved in and be able to calculate required thickness of rigid and flexible pavements 3. 3 AASHTO Pavement Design Method Considerations Pavement Performance Traffic Roadbed Soil Materials of Construction Environment Drainage Reliability Life-Cycle Costs Shoulder Design 4. 4 Two Categories of Roadway Pavements Rigid Pavement Flexible Pavement Rigid Pavement Typical Applications High volume traffic lanes Freeway to freeway connections Exit ramps with heavy traffic 5. 5 Advantages of Rigid Pavement Good durability Long service life Withstand repeated flooding and subsurface water without deterioration 6. 6 Disadvantages of Rigid Pavement May lose non-skid surface with time Needs even sub-grade with uniform settling May fault at transverse joints Requires frequent joint maintenance 7. 7 Flexible Pavement Typical Applications Traffic lanes Auxiliary lanes Ramps Parking areas Frontage roads Shoulders 8. 8 Advantages to Flexible Pavement Adjusts to limited differential settlement Easily repaired Additional thickness added any time Non-skid properties do not deteriorate Quieter and smoother Tolerates a greater range of temperatures 9. 9 Disadvantages of Flexible Pavement Loses some flexibility and cohesion with time Needs resurfacing sooner than PC concrete Not normally chosen where water is expected 10. 10 Basic AASHTO Flexible Pavement Design Method Determine the desired terminal serviceability, pt Convert traffic volumes to number of equivalent 18-kip single axle loads (ESAL) Determine the structural number, SN Determine the layer coefficients, ai Solve layer thickness equations for individual layer thickness 11. 11 Basic AASHTO Rigid Pavement Design Method Select terminal serviceability Determine number of ESALs Determine the modulus of sub-grade reaction Determine the slab thickness 12. 12 Variables included in Nomographs Reliability, R Incorporates a degree of certainty into design process Ensures various design alternatives will last the analysis period Resilient Modulus for Roadbed Soil, MR Generally obtained from laboratory testing 13. 13 Variables included in Nomographs Effective Modulus of Sub-Grade Reaction, k Considers: 1. Sub-base type 2. Sub-base thickness 3. Loss of support 4. Depth to rigid foundation Drainage Coefficient, mi Use in layer thickness determination Applies only to base and sub-base See Tables 20.15 (flexible) and 21.9 (rigid) 14. 14 15. 15 16. Other Growth Rates Multiple payment compound amount factor, with i = growth rate G = [(1+i)n -1]/i 16 17. 17 18. 18 19. 19 20. 20 21. 21 22. 22 23. 23 24. 24 25. 25 26. 26 27. 27 Flexible Pavement Design Pavement structure is a multi-layered elastic system, material is characterized by certain properties Modulus of elasticity Resilient modulus Poisson ratio Wheel load causes stress distribution (fig 20.2) Horizontal: tensile or compressive Vertical: maximum are compressive, decrease with depth Temperature distribution: affects magnitude of stresses 28. 28 Components Sub-grade (roadbed) course: natural material that serves as the foundation of the pavement structure Sub-base course: above the sub-grade, superior to sub-grade course Base course: above the sub base, granular materials such as crushed stone, crushed or uncrushed slag, gravel, and sand Surface course: upper course of the road pavement, should withstand tire pressures, resistant to abrasive forces of traffic, provide skid- resistant driving surface, prevent penetration of surface water 3 inches to > 6 inches 29. 29 Economic Analysis Different treatments results in different designs Evaluate cost of different alternatives 30. 30 Sensitivity Analysis Input different values of traffic volume Compare resulting differences in pavement Fairly significant differences in ADT do not yield equally significant differences in pavement thickness 31. 31 OTHER ISSUES Drainage Joints Grooving (noise vs. hydroplaning) Rumble strips Climate Level and type of usage 32. 32 FAILURE EXAMPLES Primarily related to design or life- cycle, not construction All images from Distress Identification Manual for the Long- Term Pavement Performance Program, Publication No. FHWA-RD- 03-031, June 2003 33. 33 FATIGUE CRACKING 34. 34 RUTTING 35. 35 SHOVING 36. 36 PUMPING 37. 37 EXAMPLES http://training.ce.washington.edu/wsdot http://training.ce.washington.edu/wsdot

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