sensitivity of the m-e pavement design guides in … systematic approach to design, more...
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Sensitivity of the M-E Pavement Design Guides in Indiana
Tommy E. Nantung INDOT Research and Development Division
Current Pavement Design Procedures
DO YOU KNOW WHY YOUR TRIAL DESIGNS FAIL?
Current Pavement Design Procedure Less systematic approach to design, more
deterministic Push the button or plug values in
nomograph/formula The results are ◦ Thickness design ◦ Faulting check ◦ Structural numbers
No relationship between design and predicted performance
In General
The current pavement design procedure is “Plug-And-Play”, the rest of them you don’t have to think about.
However, the current pavement design already served us for more than five decades
The current pavement design is also only “nationally” calibrated
Paradigm Shift in Pavement Design
More demanding on return-on-investment Design to meet the design life with a
certain performance expectation ◦ Long-term Budgeting
Not necessarily to extend the pavement life ◦ Balancing between performance and cost, you
decide
Mechanistic-Empirical Design Climate Traffic
Materials
Structure
Distress Response Time
Damage
Damage Accumulation
MEPDG Process Inputs
Traffic Climate Structure
Selection of Trial Design
Structural Responses (σ, ε, δ)
Calibrated Damage-Distress Models Distresses Smoothness
Performance Verification Failure criteria
Design Reliability
Design Requirements
Satisfied? No
Feasible Design
Rev
ise
trial
des
ign
Damage Accumulation with Time
Yes
Sensitivity Analysis – Slab Thickness
0 10 20 30 40 50 60 70 80 90 100
12 13 14 15 16 17 18 19 20
Joint spacing, ft
Perc
ent s
labs
cra
cked
8-in slab 9-in slab 10-in slab
11-in slab
Sensitivity Analysis – Predicted Cracking for 95% Reliability
0
5
10
15
20
25
30
9.4 9.5 9.6 9.7 9.8 9.9 10.0 10.1
Slab thickness, in
Perc
ent s
lab
crac
king
Target level of cracking
Design Thickness
15’ joint spacing 19 million trucks, TTC8 (30 million ESALs)
Sensitivity Analysis - Predicted Cracking for 50% Reliability
0
5
10
15
20
9.0 9.2 9.4 9.6 9.8 10.0 10.2 10.4
Slab thickness, in
Perc
ent s
labs
cra
cked
Target design level of cracking
Predicted cracking for 95% reliability design thickness
15’ joint spacing 19 million trucks, TTC8 (30 million ESALs)
Sensitivity Analysis – Traffic Capacity at 50% Reliability
0
10
20
30
40
50
60
70
80
90
9.0 9.2 9.4 9.6 9.8 10.0 10.2 10.4 Slab thickness, in
Traf
fic, m
illio
ns o
f tru
cks
(TTC
8)
Allowable traffic at design thickness (48 million trucks [76 million ESALs])
Design traffic: 19 million trucks 30 million ESALs
Target design level of slab cracking = 15%
Sensitivity Analysis – Distance of Wheelpath from Edge
0
5
10
15
20
25
30
10 12 14 16 18 20 22 24
Mean wheelpath, in from slab edge
Per
cent
sla
bs c
rack
ed
Default mean wheelpath
Traffic wander standard deviation = 10 in
Sensitivity Analysis – Standard Deviation in Distance Wheelpath
0
5
10
15
20
25
30
7 8 9 10 11 12 13 Traffic wander standard deviation, in
Per
cent
sla
bs c
rack
ed
Mean wheelpath = 12 in
Mean wheelpath = 18 in
Mean wheelpath = 22 in
Sensitivity Analysis – Concrete Modulus of Rupture
0
10
20
30
40
50
60
70
580 600 620 640 660 680 700 720 740
28-day PCC modulus of rupture, psi
Perc
ent s
labs
cra
cked
Predicted cracking for 95% reliability design
Design average 28-day PCC modulus of rupture (690 psi)
Predicted cracking for 50% reliability design
Sensitivity Analysis – PCC Modulus of Elasticity
0
10
20
30
40
50
60
70
3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8
28-day PCC elastic modulus, million psi
Perc
ent s
labs
cra
cked
Predicted cracking for 95% reliability design
Target design level of cracking
Sensitivity Analysis – PCC Coefficient of Thermal Expansion
0
5
10
15
20
0 5 10 15 20 25 30
Age, years
Perc
ent s
labs
cra
cked
6.5x10-6/F
6.0x10-6/F
5.5x10-6/F
5.0x10-6/F
Sensitivity Analysis – Combined Effect of PCC CTE and E
0 5
10 15 20 25 30 35 40 45 50
9.0 9.2 9.4 9.6 9.8 10.0 10.2 10.4
Slab thickness, in
Perc
ent s
labs
cra
cked
Predicted cracking for 95% reliability design CTE = 5.5x10-6 / degF 28-day Epcc = 4.4 Mpsi
CTE = 6.0x10-6 / degF 28-day Epcc = 4.0 Mpsi
Sensitivity Analysis – Effect of Climatic Zone
0
5
10
15
20
25
30
0 5 10 15 20 25 30
Pavement age, years
Perc
ent s
labs
cra
cked
Florida (wet-nonfreeze)
Arizona (dry-nonfreeze) North Dakota
(dry-freeze)
Illinois (wet-freeze)
Sensitivity Analysis – Base Type
0
2
4
6
8
10
0 5 10 15 20 25 Pavement age, years
Perc
ent s
labs
cra
cked
Asphalt-treated base
Aggregate base
Cement-treated base
Sensitivity Analysis – Effect of Edge Support
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Age, years
Perc
ent s
labs
cra
cked
Tied PCC shoulder LTE = 40%
Tied PCC shoulder LTE = 70%
AC shoulder
Widened slab
Sensitivity Analysis – Reliability levels for Road Test Traffic
8.0
8.5
9.0
9.5
10.0
10.5
11.0
50 55 60 65 70 75 80 85 90 95 100
Reliability, percent
Des
ign
thic
knes
s, in
AASHTO 93
2002 Design Guide
Sensitivity Analysis – Reliability for Moderately High Traffic
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
50 55 60 65 70 75 80 85 90 95 100 Reliability, percent
Des
ign
thic
knes
s, in
AASHTO 93
2002 Design Guide
19 million trucks (TTC 8 [30 million ESALs)
Concrete Pavement Design Inputs - Sensitivity Analysis
Over 30 parameters specifically related to JPCP
Sensitivity analysis is based on INDOT current practice
Base design inputs were created for comparisons
Each parameter was varied independently Distresses and performance indicator
(faulting, cracking, and IRI) are compared
Concrete Pavement Design Inputs - Sensitivity Analysis 17 design inputs were chosen to be
analyzed Strength values in hierarchical inputs ◦ Level 3: 28-day Modulus of Rupture or
Compressive Strength ◦ Level 2: Compressive strength at 7, 14, 28, and
90 days + 20-year/28-days ratio ◦ Level 1: Modulus of Rupture and Modulus of
Elasticity at 7, 14, 28, and 90 days + 20-year/28-days ratio
Concrete Pavement Design Inputs - Sensitivity Analysis
Parameter Roughness Faulting Percent Slabs Cracked
Level 3 Modulus of Rupture S NS VS
Compressive Strength S NS VS
Level 2 Compressive Strength S NS VS
20-year/28-day Ratio S NS VS
Level 1 Modulus of Rupture S NS VS
Modulus of Elasticity S NS VS
20-year/28-day Ratio S NS VS
Concrete Pavement Design Inputs - Sensitivity Analysis
Parameter Roughness Faulting Percent Slabs Cracked
Permanent Curl/Warp Effective Temperature Difference
VS VS VS
Joint Spacing VS VS VS
Dowel Bar Diameter MS MS NS
Pavement Thickness S MS VS
Poisson’s Ratio MS MS S
Coefficient of Thermal Expansion VS VS VS
Thermal Conductivity S MS VS
Concrete Pavement Design Inputs - Level 3 vs Level 1 Modulus of Rupture
200
300
400
500 600 700 800 90028 day Flexural Strength (psi)
IRI (
in/m
i)
Level 1 IRILevel 1 IRI ReliabilityLevel 3 IRILevel 3 IRI ReliabiltyLimit
Reliability
Traffic Information
Trial thickness design
Unbound Materials
Unbound Materials – Passing #200
Blindly implement the MEPDG
Purely trial and error Thickness design can be achieved by
“luck” only May not be the most efficient design May not achieve any design at all
Reliability Issue
Sensitivity of IRI
Sensitivity of Faulting
JPCP Smoothness Model (Empirical)
IRI = IRII + 0.8203*cracking + 0.4417*Spalling + 1.4929*Faulting + 25.24*SF
where IRII = Initial IRI PUNCH = Number of mid- to high-severity punchouts/km PATCH = Number of mid- to high-severity flexible or rigid patching SF = Site Factor
= AGE*(1 + FI)(1 + P0.075)/106
AGE = pavement age, yr FI = Freezing index, oC days P0.075 = percent subgrade material passing 0.075-mm sieve
Components of Curling Stresses Applied with Traffic Load in FEM Analysis
0.00.1
0.20.3
0.40.5
0.60.7
0.80.9
1.0
0 5 10 15 20 25 30 35
Relative Temperature, °F
De
pth
(1
.0 =
su
rfa
ce
)
0 20% 40% 60% 80% 100%
Actual Temperature Gradient
Built-in Curling Moisture Gradient
ShrinkageinBuiltActual TTTT ∆+∆+∆=∆ −
ME Design Procedure – Structural Analysis and Pavement Response
Concrete Slab (JPCP, CRCP)
Base Course (unbound, stabilized)
Subbase (unbound, stabilized)
Compacted Subgrade
Natural Subgrade
Bedrock
Ec
Ebase
Lay
ered
syst
em w
ith
effe
ctiv
e k-
valu
e
Calculate pavement responses
Stresses Deformations
at critical locations
ME Design Procedure for JPCP, cont. Calculate fatigue damage for each increment ◦ Each increment is a unique combination of:
Time (age, season) & PCC strength
Loads (number, axle type, axle weight) Equivalent thermal gradients (temperature and
shrinkage) Traffic path (wander location)
NLoadsofNumberAllowablenLoadsofNumberActualDamageFatigue,
,=
ME Design Procedure for JPCP, cont.
∑ ∑ ∑ ∑ ∑ ∑=i j k l m n ijklmn
ijklmn
Nn
DamageFatigue
nijklmn = Applied number of load applications at condition i,j,k,… Nijklmn = Allowable number of load applications at condition i,j,k,… i = Age ; j = Season; k = Axle combination l = Load level; m = Temperature gradient; n = Traffic path
Accumulate Fatigue Damage (Incremental Approach)
( )22.1
*0.2
=
total
rMNLogσ
*
* ******
****** *
*
*****
** * *** ***
*****
********
**** ** *
*1E+07
1E+06
1E+05
1E+04
1E+03
1E+02
1E+01
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2.0
AASHO Extended AASHO (not used in dev.)
CORPS
Num
ber
of S
tres
s Rep
etiti
ons
Stress Ratio, (σ/MR)
Fatigue Models
How does ME Design Procedure Predict Performance? (cont.) Step 5: Correlate damage to distress ◦ Predict distresses with mechanistic-based
models that are calibrated with field data 1. JPCP transverse cracking
Top-down cracking Bottom-up cracking
2. JPCP faulting 3. IRI for smoothness
Distress Prediction from Model Calibrated using LTPP Data
Age
Distress
Time Damage
Distress Damage
Base
Subgrade
Critical stress region at bottom of slab
JPCP Bottom-Up Cracking – (Mid-slab Load + Positive Curl/Warp Condition)
Base
Subgrade
Critical stress region at top of slab
JPCP Top Down Cracking (Joint Load + Negative Curl/Warp Condition)
Correlate Damage to Cracking
Accumulated damage at each increment is correlated to field cracking based on the distress model calibrated using LTPP data
7.11100
−+=
DamageCracking
JPCP Joint Faulting Mechanism
Direction of Traffic
Foundation: Base and Subgrade
Joint Opening, LTE
δ(unloaded)
δ(loaded)
Overall Faulting Model Flowchart Site conditions/
Trial design inputs: Dowel diameter, base type,
PCC thickness
Calculate faulting increment and joint wear-out at end of each month
Calculate loaded and unloaded corner deflections
Joint opening, LTE calculation
Calculate differential energy, DE (Main Structural Response)
Calculate total faulting
Faulting Prediction – Maximum Faulting
P200 = Percent passing #200 sieve in Subgrade
EROD - erodobility index
[ ] 6)/*(*5*1(**0 200512C
serod
curling PWetdaysPLogCLogCFaultMax += δ
C1 = 1.29 C2 = 1.1
C5 = 250 C6 = 0.40
C7 = 1.20 C8 = 400
)*( 25.02112 FRCCC +=
Faulting Prediction, cont.
Calculate faulting increment at the end of each month: ∆FAULT = faulting increment FAULTMAX = maximum faulting FAULT = cumulative faulting at beginning of month DE = differential energy (for all axle type and load level C3 = 0.001725 C4 = 0.0008
nDEFaultFaultMaxCFault *)(* 234 −=∆
)*( 25.04334 FRCCC +=
Faulting Prediction, cont. Calculate faulting level at the end of each
month:
where
FAULTl+1 = faulting at the end of the month FAULTl = faulting at the beginning of the month DFAULT = faulting increment
DFAULTFAULTFAULT ll +=+1
Now, change the passing #200
Now, change the passing #200
Now, change the traffic information
Now, change the traffic information
Now, change the slab dimensions
Conclusions
Have to know the “black box” before you can implement the MEPDG
Have to know pavement materials and pavement structure to be able to design pavement
Know the sensitivity parameters for your “local” state
Local calibration will not solve all the issues
Conclusions
Some very sensitive parameters are impossible to be locally calibrated ◦ Soil type is the most difficult ◦ Some parameters are “hidden” somewhere
“Verification” is so far the best method to implement the MEPDG right away
Do comprehensive trial runs to get the “feel” on how the parameters influence the outcomes