1. Mechanistic-
Mechanistic-Empirical
Pavement Design
P D i
David P. Orr, PE
Cornell Local Roads Program
Co oc o ds og

2. NYS 180 - LaFargeville

3. NYS 180 - LaFargeville
800 AADT

4. Q: How thick are the asphalt and
gravel layers?
NYS 180 - L F
LaFargeville
ill
800 AADT

5. 17 ½ in.

6. ME Pavement Design
Why 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. Why Roads Fail

8. What is a road?

9. Road Structure
Surface
Base
Subbase
S bb
Subgrade

10. Vehicle Loads
Load
Pavement
Subgrade

11. Pavement Deflection
Load
Pavement
Subgrade

12. Pavement Deflection
Load
T T
Pavement C
C
C
T
Subgrade

14. Pavement Fatigue

15. Pavement Fatigue
45° 90° 180°

16. Pavement Failure?
Potholes
Alligator cracking
Corrugations
Edge raveling
Rutting

17. Drainage

18. Pavement Design Methods

19. Pavement Design Methods
Experience
Catalog
Empirical
E ii l
Mechanistic-
Mechanistic-Empirical

20. Experience

21. NYSDOT Comprehensive
Pavement Design Manual
Black or white – Asphalt or PCC
Mr – Subgrade resilient modulus
ESALs
ESAL – 50 year design life
d i lif

22. 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

23. Mechanistic-
Mechanistic-Empirical (M-E)
(M-
Strain Base Fatigue Failure Criteria
T
T
V

24. Q: Which pavement design
method do you use?
Experience
Catalog
Empirical
E ii l
Mechanistic-
Mechanistic-Empirical

25. M-E Pavement Design

26. Critical Fatigue Concepts
Determine failure mode mechanistic
Select a failure criteria empirical
Develop failure
D l a f il model? d l?

27. Fatigue Failure Criteria
k2
⎛ 1 ⎞ ⎛1⎞
k3
N f = k1 ⎜
⎜ε ⎟ ⎜ ⎟
⎟ ⎝E⎠
⎝ cr ⎠
n(ε)
ln
ln(Nf)

28. Locations of Critical Strains
Load
T T
T T
C
C
C C
T
C
C
T
V

29. Two Most Common
Fatigue Failure Criteria
Tensile strain in the surface (εt) cracking
(ε
Vertical strain on the subgrade (εv) rutting
(ε

30. 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 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

31. 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
g
V
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.

32. 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 ⎠

33. Q: How many passes by a standard
automobile are needed to equal the
damage of one fully loaded 10-wheel
10-
dump truck?
5,000-
5,000-10,000

34. Elastic Layer Theory
Forward Calculation
P, a
Θ E1,η1,t1 Traffic
P = Load
R E2,η2,t2 a = Area
Pavement layers
Stress σX,Y,Z Ei = Modulus
E3,η3,t3
Strain εX Y Z
X,Y,Z
ηi = Poisson’s ratio
Poisson s
Disp. δX,Y,Z ti = Thickness
E4,η4,∞

35. Miner’s Hypothesis
yp
nf D = amount of
f
D= damage (%)
Nf

36. Simple Pavement
Asphalt 8 inches 158,000 psi
Subbase 12 inches 36,400
36 400 psi
Upper Subgrade 30 inches 14,700 psi
Lower Subgrade ∞ 13,300 psi

37. ⎛ 1.281
1⎞
3.9492
ESAL Load
N 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

38. ESAL Loads
ESAL Load Nf
nf
D= 9,000 lbs 9,420,000
Nf
5,000 AADT nf =4,710,000

39. Single Load
nf 4,710,000
D= = = 50%
N f 9,420,000

40. Miner’s Hypothesis
yp
n1 n2
ε D= + ≤1
(log
scale))
N1 N 2
ε2 Load level 2
ε1 Load level 1
Nf2 Nf1
Nf (log scale)

41. Miner’s Hypothesis
yp
T ,season ,...
, ,
nf
D=
Nf
∑ Di , j ,...
i =1, j =1,..
,
D ≤1

42. ME Design
Traffic Seasons
P = Load Annual
a = Area Daily
Pavement layers Long-
Long-term
Ei = Modulus Asphalt aging
ηi = Poisson’s ratio Cracking
ti = Thickness …

43. Backcalculation
The process of
converting
i
measured
pavement
deflections into
layer moduli
l d li

44. 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
modulus
Deflec
1 2nd deflection
4. Use FWD
0.1 deflection to
1,000 10,000 100,000 estimate
Modulus, psi
M d l i modulus

45. The Need for Seasons

46. Seasonal Changes
Frozen Rapid drainage Refreezing
Thawing Slow recovery
Asphalt Surface and Base
Granular Subbase
Weather Affected Subgrade
Subgrade
Jan. Dec.

47. Seasonal Models
Modulus
s
J A J O
Date
Subbase Seasonal Subgrade Subgrade

48. Effect of Changing
Season Lengths
Initial inputs
7 days of Spring thaw
Nf = 660 000 ESAL
660,000 ESALs
Increase Spring-thaw from 7 to 28 days
Spring-
Nf = 490 000 ESALs
490,000
26.2% decrease in lifespan

49. Number of Days of Thaw

50. Seasonal Response Techniques
Calculate average annual response
Detailed hourly calculations
Representative year
R i

51. AASHTO Pavement Design Guide
−2.32
u f = 1.18 x10 xM R
8
uf - Relative damage,
damage
MR - Roadbed soil
resilient modulus (psi)

52. Q: Which layers in the pavement
change seasonally?
All of them
dulus
Mod
J A J O
Date
Subbase Seasonal Subgrade Subgrade

53. Expanded Seasonal Pavement
Moduli Models

54. FWD Testing Sites
Phase I
Ph
Phase II
Frost Depth > 1,100 mm
Frost Depth < 600 mm
Plasticity Index > 12

55. ME-
ME-PDG

56. Critical Variables
Traffic
Need to account for overloads
Weather
Daily changes
Seasonality
Pavement structure & materials
Thickness
Quality of construction
Long-
Long-term changes
All variables

57. M-E Design Guide

59. Questions

60. Q: What are the primary 2 failure
modes for asphalt pavement?
Tensile strain in the surface
Fatigue cracking
Compressive strain on the subgrade
C i i h b d
Subgrade rutting

61. Q: When is a pavement the strongest?
Winter

62. Q: When is a pavement the weakest?
Spring thaw

63. Q: Backcalculation should be
used on all pavements?
No

64. Thank You
David Orr
Senior Engineer
Cornell L l R d P
C 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