Mechanistic Empirical Pavement Design

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Mechanistic Empirical Pavement Design

  1. 1. Mechanistic-Mechanistic-Empirical Pavement Design P D i David P. Orr, PE Cornell Local Roads Program Co oc o ds og
  2. 2. NYS 180 - LaFargeville
  3. 3. NYS 180 - LaFargeville 800 AADT
  4. 4. Q: How thick are the asphalt and gravel layers? NYS 180 - L F LaFargeville ill 800 AADT
  5. 5. 17 ½ in.
  6. 6. ME Pavement DesignWhy roads fail Pavement design methods Mechanistic- Mechanistic Empirical M h i i -E i i l pavement d i design The need for seasons ME- ME-PDG
  7. 7. Why Roads Fail
  8. 8. What is a road?
  9. 9. Road StructureSurface Base Subbase S bb Subgrade
  10. 10. Vehicle Loads LoadPavement Subgrade
  11. 11. Pavement Deflection LoadPavement Subgrade
  12. 12. Pavement Deflection Load T TPavement C C C T Subgrade
  13. 13. Pavement Fatigue
  14. 14. Pavement Fatigue 45° 90° 180°
  15. 15. Pavement Failure?PotholesAlligator crackingCorrugationsEdge ravelingRutting
  16. 16. Drainage
  17. 17. Pavement Design Methods
  18. 18. Pavement Design MethodsExperience Catalog Empirical E ii l Mechanistic- Mechanistic-Empirical
  19. 19. Experience
  20. 20. NYSDOT Comprehensive Pavement Design ManualBlack or white – Asphalt or PCCMr – Subgrade resilient modulusESALsESAL – 50 year design life d i lif
  21. 21. AASHTO 1993 ⎡ ΔPSI ⎤ log10 ⎢log10 W18 = ZR * So + 9.36* log10 (SN +1) − 0.20+ ⎣4.2 −1.5⎥ + 2.32* log M − 8.07 ⎦ 10 R 1094 0.40+ (SN +1)5.19
  22. 22. Mechanistic-Mechanistic-Empirical (M-E) (M-Strain Base Fatigue Failure Criteria T T V
  23. 23. Q: Which pavement design method do you use?Experience Catalog Empirical E ii l Mechanistic- Mechanistic-Empirical
  24. 24. M-E Pavement Design
  25. 25. Critical Fatigue ConceptsDetermine failure mode mechanistic Select a failure criteria empirical Develop failure D l a f il model? d l?
  26. 26. Fatigue Failure Criteria k2 ⎛ 1 ⎞ ⎛1⎞ k3 N f = k1 ⎜ ⎜ε ⎟ ⎜ ⎟ ⎟ ⎝E⎠ ⎝ cr ⎠ n(ε)ln ln(Nf)
  27. 27. Locations of Critical Strains Load T T T T C C C C T C C T V
  28. 28. Two Most Common Fatigue Failure CriteriaTensile strain in the surface (εt) cracking (ε Vertical strain on the subgrade (εv) rutting (ε
  29. 29. 3.9492 ⎛ ⎛E⎞ 1.281 1 ⎞ N f surface (106 ) = ⎜ 0.00432 C ⎜ ⎟ ⎟ ⎜ ⎝ E ⎠ εt ⎟ ⎝ ⎠ Asphalt Horizontal Tensile Strain Criteria 10,000 10 000 strain) train (micros Average Coefficients K = 220.3 a = 4.260 1,000 b = -0.85 (Asph. Inst.) E 435 100 E = 435,100 psiHorizontal StH 100 100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000 Number f Repetitions N b of R titi Asphalt Inst. TRL - 1 Average NAASRA Shell Denmark DTU
  30. 30. 3.902 ⎛ 1 ⎞ N f subgrade (10 ) = ⎜ 619.5 ⎜ 6 ⎟ ⎟ ⎝ εV ⎠ Subgrade Vertical Compressive Strain Criteria 10,000 ain)Vertical Strai (microstra 1,000 in Average Coefficients gV K = 619.5 a = 3.902 100 100 1,000 , 10,000 , 100,000 , 1,000,000 , , 10,000,000 , , 100,000,000 , , Number of Repetitions Denmark DTU Shell Average Nottingham Dorman & Metcalf TRL Asphalt Inst.
  31. 31. 3.902 ⎛ 1 ⎞N f subgrade (10 ) = ⎜ 619.5 6 ⎜ ⎟ ⎟ ⎝ εV ⎠ ~4 ⎛ 1 ⎞ N f subgrade (10 ) ∝ ⎜ 6 ⎜ε ⎟⎟ ⎝ V⎠ ~4 N f subgrade (car ) ⎛ ε V (truck ⎞ ∝⎜ ⎜ ε (car ) ⎟ ⎟N f subgrade (truck ) ⎝ V ⎠
  32. 32. Q: How many passes by a standardautomobile are needed to equal thedamage of one fully loaded 10-wheel 10- dump truck?5,000-5,000-10,000
  33. 33. Elastic Layer Theory Forward Calculation P, a Θ E1,η1,t1 Traffic P = Load R E2,η2,t2 a = Area Pavement layersStress σX,Y,Z Ei = Modulus E3,η3,t3Strain εX Y Z X,Y,Z ηi = Poisson’s ratio Poisson sDisp. δX,Y,Z ti = Thickness E4,η4,∞
  34. 34. Miner’s Hypothesis yp nf D = amount of fD= damage (%) Nf
  35. 35. Simple PavementAsphalt 8 inches 158,000 psiSubbase 12 inches 36,400 36 400 psiUpper Subgrade 30 inches 14,700 psiLower Subgrade ∞ 13,300 psi
  36. 36. ⎛ 1.281 1⎞ 3.9492 ESAL LoadN f surface (10 ) = ⎜ 0.00432 C ⎛ E ⎟ ⎜ ⎞ 6 ⎟ ⎜ ⎝ E ⎠ ⎟ εt ⎠ 9,000 9 000 lbs ⎝ Asphalt Horizontal Tensile Strain Criteria 10,000 10 000 strain) train (micros Average Coefficients K = 220.3 a = 4.260 1,000 b = -0.85 (Asph. Inst.) E 435 100 E = 435,100 psi Horizontal St H 100 100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000 Number f Repetitions N b of R titi Asphalt Inst. TRL - 1 Average NAASRA Shell Denmark DTU
  37. 37. ESAL Loads ESAL Load Nf nfD= 9,000 lbs 9,420,000 Nf 5,000 AADT nf =4,710,000
  38. 38. Single Load nf 4,710,000D= = = 50% N f 9,420,000
  39. 39. Miner’s Hypothesis yp n1 n2 ε D= + ≤1 (logscale)) N1 N 2 ε2 Load level 2 ε1 Load level 1 Nf2 Nf1 Nf (log scale)
  40. 40. Miner’s Hypothesis yp T ,season ,... , , nfD= Nf ∑ Di , j ,... i =1, j =1,.. , D ≤1
  41. 41. ME DesignTraffic Seasons P = Load Annual a = Area DailyPavement layers Long- Long-term Ei = Modulus Asphalt aging ηi = Poisson’s ratio Cracking ti = Thickness …
  42. 42. BackcalculationThe process ofconverting imeasuredpavementdeflections intolayer modulil d li
  43. 43. How Backcalculation 1. Select Works… Pavement layer / FWD Sensor 100 2. Use S d 2 U Seed Value Initial ction, mils deflection m 10 3. Select 2nd modulusDeflec 1 2nd deflection 4. Use FWD 0.1 deflection to 1,000 10,000 100,000 estimate Modulus, psi M d l i modulus
  44. 44. The Need for Seasons
  45. 45. Seasonal ChangesFrozen Rapid drainage Refreezing Thawing Slow recovery Asphalt Surface and Base Granular Subbase Weather Affected Subgrade SubgradeJan. Dec.
  46. 46. Seasonal ModelsModulus s J A J O Date Subbase Seasonal Subgrade Subgrade
  47. 47. Effect of Changing Season LengthsInitial inputs 7 days of Spring thaw Nf = 660 000 ESAL 660,000 ESALsIncrease Spring-thaw from 7 to 28 days Spring- Nf = 490 000 ESALs 490,000 26.2% decrease in lifespan
  48. 48. Number of Days of Thaw
  49. 49. Seasonal Response TechniquesCalculate average annual response Detailed hourly calculations Representative year R i
  50. 50. AASHTO Pavement Design Guide −2.32 u f = 1.18 x10 xM R 8 uf - Relative damage, damage MR - Roadbed soil resilient modulus (psi)
  51. 51. Q: Which layers in the pavement change seasonally?All of them dulus Mod J A J O Date Subbase Seasonal Subgrade Subgrade
  52. 52. Expanded Seasonal Pavement Moduli Models
  53. 53. FWD Testing Sites Phase I Ph Phase IIFrost Depth > 1,100 mmFrost Depth < 600 mmPlasticity Index > 12
  54. 54. ME-ME-PDG
  55. 55. Critical VariablesTraffic Need to account for overloadsWeather Daily changes SeasonalityPavement structure & materials Thickness Quality of constructionLong-Long-term changes All variables
  56. 56. M-E Design Guide
  57. 57. Questions
  58. 58. Q: What are the primary 2 failure modes for asphalt pavement?Tensile strain in the surface Fatigue crackingCompressive strain on the subgradeC i i h b d Subgrade rutting
  59. 59. Q: When is a pavement the strongest? Winter
  60. 60. Q: When is a pavement the weakest? Spring thaw
  61. 61. Q: Backcalculation should be used on all pavements?No
  62. 62. Thank You David Orr Senior EngineerCornell L l R d PC ll Local Roads Program 416 Riley-Robb Hall Riley- Ithaca, NY 14853 Ithaca 607-255- 607-255-8033 dpo3@cornell.edu p @ www.clrp.cornell.edu

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