28 pavement design

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flexible pavment design

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  • INSERT SLIDE HERE TO SHOW THE FORMULA AND HOW TO CALCULATE
  • 28 pavement design

    1. 1. Pavement Design CE 453 Lecture 28
    2. 2. Objectives <ul><li>Understand and complete ESAL calculation </li></ul><ul><li>Know variables involved in and be able to calculate required thickness of rigid and flexible pavements </li></ul>
    3. 3. AASHTO Pavement Design Method Considerations <ul><li>Pavement Performance </li></ul><ul><li>Traffic </li></ul><ul><li>Roadbed Soil </li></ul><ul><li>Materials of Construction </li></ul><ul><li>Environment </li></ul><ul><li>Drainage </li></ul><ul><li>Reliability </li></ul><ul><li>Life-Cycle Costs </li></ul><ul><li>Shoulder Design </li></ul>
    4. 4. <ul><li>Two Categories of Roadway Pavements </li></ul><ul><li>Rigid Pavement </li></ul><ul><li>Flexible Pavement </li></ul><ul><li>Rigid Pavement Typical Applications </li></ul><ul><li>High volume traffic lanes </li></ul><ul><li>Freeway to freeway connections </li></ul><ul><li>Exit ramps with heavy traffic </li></ul>
    5. 5. <ul><li>Advantages of Rigid Pavement </li></ul><ul><li>Good durability </li></ul><ul><li>Long service life </li></ul><ul><li>Withstand repeated flooding and subsurface water without deterioration </li></ul>
    6. 6. <ul><li>Disadvantages of Rigid Pavement </li></ul><ul><li>May lose non-skid surface with time </li></ul><ul><li>Needs even sub-grade with uniform settling </li></ul><ul><li>May fault at transverse joints </li></ul><ul><li>Requires frequent joint maintenance </li></ul>
    7. 7. Flexible Pavement Typical Applications <ul><li>Traffic lanes </li></ul><ul><li>Auxiliary lanes </li></ul><ul><li>Ramps </li></ul><ul><li>Parking areas </li></ul><ul><li>Frontage roads </li></ul><ul><li>Shoulders </li></ul>
    8. 8. <ul><li>Advantages to Flexible Pavement </li></ul><ul><li>Adjusts to limited differential settlement </li></ul><ul><li>Easily repaired </li></ul><ul><li>Additional thickness added any time </li></ul><ul><li>Non-skid properties do not deteriorate </li></ul><ul><li>Quieter and smoother </li></ul><ul><li>Tolerates a greater range of temperatures </li></ul>
    9. 9. <ul><li>Disadvantages of Flexible Pavement </li></ul><ul><li>Loses some flexibility and cohesion with time </li></ul><ul><li>Needs resurfacing sooner than PC concrete </li></ul><ul><li>Not normally chosen where water is expected </li></ul>
    10. 10. Basic AASHTO Flexible Pavement Design Method <ul><li>Determine the desired terminal serviceability, p t </li></ul><ul><li>Convert traffic volumes to number of equivalent 18-kip single axle loads (ESAL) </li></ul><ul><li>Determine the structural number, SN </li></ul><ul><li>Determine the layer coefficients, a i </li></ul><ul><li>Solve layer thickness equations for individual layer thickness </li></ul>
    11. 11. Basic AASHTO Rigid Pavement Design Method <ul><li>Select terminal serviceability </li></ul><ul><li>Determine number of ESALs </li></ul><ul><li>Determine the modulus of sub-grade reaction </li></ul><ul><li>Determine the slab thickness </li></ul>
    12. 12. Variables included in Nomographs <ul><li>Reliability, R </li></ul><ul><ul><li>Incorporates a degree of certainty into design process </li></ul></ul><ul><ul><li>Ensures various design alternatives will last the analysis period </li></ul></ul><ul><li>Resilient Modulus for Roadbed Soil, MR </li></ul><ul><ul><li>Generally obtained from laboratory testing </li></ul></ul>
    13. 13. Variables included in Nomographs <ul><li>Effective Modulus of Sub-Grade Reaction, k </li></ul><ul><ul><li>Considers: </li></ul></ul><ul><ul><ul><li>Sub-base type </li></ul></ul></ul><ul><ul><ul><li>Sub-base thickness </li></ul></ul></ul><ul><ul><ul><li>Loss of support </li></ul></ul></ul><ul><ul><ul><li>Depth to rigid foundation </li></ul></ul></ul><ul><li>Drainage Coefficient, m i </li></ul><ul><ul><li>Use in layer thickness determination </li></ul></ul><ul><ul><li>Applies only to base and sub-base </li></ul></ul><ul><ul><li>See Tables 20.15 (flexible) and 21.9 (rigid) </li></ul></ul>
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    15. 15.
    16. 16. Other Growth Rates <ul><li>Multiple payment compound amount factor, with i = growth rate </li></ul><ul><li>G = [(1+i) n -1]/i </li></ul>
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    27. 27. Flexible Pavement Design <ul><li>Pavement structure is a multi-layered elastic system, material is characterized by certain properties </li></ul><ul><ul><li>Modulus of elasticity </li></ul></ul><ul><ul><li>Resilient modulus </li></ul></ul><ul><ul><li>Poisson ratio </li></ul></ul><ul><li>Wheel load causes stress distribution (fig 20.2) </li></ul><ul><ul><li>Horizontal: tensile or compressive </li></ul></ul><ul><ul><li>Vertical: maximum are compressive, decrease with depth </li></ul></ul><ul><ul><li>Temperature distribution: affects magnitude of stresses </li></ul></ul>
    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 <ul><li>Different treatments results in different designs </li></ul><ul><li>Evaluate cost of different alternatives </li></ul>
    30. 30. Sensitivity Analysis <ul><li>Input different values of traffic volume </li></ul><ul><li>Compare resulting differences in pavement </li></ul><ul><li>Fairly significant differences in ADT do not yield equally significant differences in pavement thickness </li></ul>
    31. 31. OTHER ISSUES <ul><li>Drainage </li></ul><ul><li>Joints </li></ul><ul><li>Grooving (noise vs. hydroplaning) </li></ul><ul><li>Rumble strips </li></ul><ul><li>Climate </li></ul><ul><li>Level and type of usage </li></ul>
    32. 32. FAILURE EXAMPLES <ul><li>Primarily related to design or life-cycle, not construction </li></ul><ul><li>All images from Distress Identification Manual for the Long-Term Pavement Performance Program , Publication No. FHWA-RD-03-031, June 2003 </li></ul>
    33. 33. FATIGUE CRACKING
    34. 34. RUTTING
    35. 35. SHOVING
    36. 36. PUMPING
    37. 37. EXAMPLES <ul><li>http://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-7_body.htm </li></ul><ul><li>http://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-8_body.htm </li></ul>

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