Case Studies Using Falling WeightDeflectometer Data with Mechanistic‐Empirical
Design and Analysis
l f
Design and Analysis
International Symposium on Pavement PerformanceTrends, Advances, and Challenges
December 5, 2011, Tampa, FL
Presented by:Linda M. Pierce, PhD, PE
Outline
• Project purposeProject purpose
• Use of deflection data in the MEPDG
• Case studies
Project Purpose
• FHWA study DTFH61‐06‐C‐00046FHWA study DTFH61 06 C 00046
• Release of MEPDG and heightened need for
characterizing existing
layersy
• COTR ‐ Nadarajah “Siva”
Sivaneswaran
Project Reports
Use of Deflection Data in MEPDG
• Backcalculated moduli onlyBackcalculated moduli only
• Level 1 materials characterization only
– No internal MEPDG forward or backcalculation
proceduresp
Flexible Pavements
• Dynamic modulus of HMA layersDynamic modulus of HMA layers
• Resilient modulus of chemically stabilized layers
• Resilient modulus of unbound layers
– Non‐linear considered, but not calibrated, and not , ,
recommended
• Elastic modulus of the bedrock layer
Rigid Pavements
• Elastic modulus of the concrete and base layersElastic modulus of the concrete and base layers
• Subgrade k‐value
• Concrete flexural strength
– Determined from the backcalculated concrete
elastic modulus
Characterization of HMA Layer
1. Conduct FWD testingg
2. Determine mix properties from cores (air voids, AC%,
d ti i it t )gradation, viscosity parameters)
3. Determine undamaged dynamic modulus
4. Estimate fatigue damage (using results from step 1 & 3)
5. Calculate α’ – f (mix gradation parameters)5. Calculate α f (mix gradation parameters)
6. Determine field damaged dynamic modulus
Characterization of HMA Layer
Characterization of PCC Layer
• Effective k‐valueEffective k value
– Composite stiffness of all
layers beneath the base
– Internal conversion from
backcalculated layer moduli
– Backcalculated subgrade modulus not directly
used in the MEPDG
Characterization of Stabilized Layer
• Backcalculated moduliBackcalculated moduli
– Assumed to be at time of overlay application
– Reduced based on current condition of stabilized
layer and surfacey
– f (alligator cracking, reflective cracking)
Characterization of Stabilized Layer
Characterization of Unbound Layers
• Backcalculated moduliBackcalculated moduli
• Adjusted to laboratory values
– 0.67 for granular layers
– 0.40 for subgrade layersg y
– Other materials see Table 1
Case Studies
• LTPP sectionsLTPP sections
• Backcalculation methods
– Flexible: Evercalc, MODTAG, MICHBACK
– Rigid: AREA methodg
• MEPDG v 1.003
– Nationally calibrated models only
Case Studies ‐ HMA
• LTPP Section 30‐0100LTPP Section 30 0100
– Great Falls, Montana
– Interstate 15
– 4‐in HMA over 8‐in aggregate basegg g
– Overall pavement condition: Fair condition
– Rutting
• Rehabilitation type evaluated: HMA overlayyp y
Case Studies ‐ HMA
S i Layer Moduli, MPa (lb/in2)Scenario y , ( / )HMA Base Subgrade
A. MEPDG Default Internal calculation
262(38,000)
100(14,500)calculation (38,000) (14,500)
B. MODTAG(uncorrected 3 layer)
4,195(608,500)
115(16,700)
148(21,500)
C MODTAG 4 195 72 52C. MODTAG(corrected 3 layer)
4,195(608,500)
72(10,400)
52(7,500)
D. Evercalc/MICHBACK(corrected 3 layer)
4,116(597 000)
52(7 500)
62(9 000)(corrected 3 layer) (597,000) (7,500) (9,000)
E. LTPP LaboratoryTesting Results
2,413 (350,000)
91(13,200)
27(3,900)
F MODTAG 4 075 84 43F. MODTAG(corrected 4 layer)
4,075(591,000)
84(12,200)
43(6,300)
Case Studies ‐ HMA
Predicted Distress Distress Quantity (Reliability)Predicted Distress A B C D E F
Terminal IRI (in/mi) 109(98)
97(100)
97(100)
97(100)
101(99)
98(100)
Long. Cracking (ft/mile) 5.2(100)
62.7(92)
69.5(91)
165.0(86)
49.4(93)
50.4(93)
Alligator Cracking (%) 0(100)
0(100)
0(100)
0(100)
0.3(100)
0(100)Alligator Cracking (%) (100) (100) (100) (100) (100) (100)
Transverse Cracking (ft/mi) 1(100)
1(100)
1(100)
1(100)
1(100)
1(100)
0 13 0 08 0 07 0 08 0 12 0 08HMA Rutting (in) 0.13(99)
0.08(100)
0.07(100)
0.08(100)
0.12(100)
0.08(100)
Total Rutting (in) 0.38(100
0.08(100)
0.08(100)
0.08(100)
0.16(100)
0.12(100)g ( ) (100 (100) (100) (100) (100) (100)
Overlay Thickness (in) 3 3 3.5 3 3 3
Case Studies – HMA ‐ Findings
• Until further studyUntil further study
– Use MEPDG provided field‐lab correction factors
– Use 30 Hz for equivalent frequency
Case Studies ‐ PCC
• LTPP Section 32‐0200LTPP Section 32 0200– Lander County, Nevada– Interstate 80– Interstate 80– 11.6‐in PCC over 25.7‐in base/subbase over 12‐in lime treated subgradelime treated subgrade
– Overall pavement condition: PoorTransverse cracking faulting– Transverse cracking, faulting
• Rehabilitation type evaluated: HMA overlay, bonded
PCC overlay, and unbonded PCC overlay
Case Studies ‐ PCC
• AlternativesAlternatives
– Laboratory determined material properties
– Backcalculated PCC dynamic elastic modulus &
dynamic k‐value for supporting layers (all layers y pp g y ( y
beneath the base)
– Backcalculated PCC dynamic elastic modulus &
dynamic k‐value for supporting layers (all layers y pp g y y
beneath the slab)
Case Studies ‐ PCC
AlternativePCC Elastic Modulus,
lb/in2 (MPa)
k‐value,lb/in2/in(kPa/mm)lb/in (MPa) (kPa/mm)
1. Laboratory determined 2,783,000(19,188)
NA
3 100 000 3101. Backcalculated PCC 3,100,000(21,359)
310(84)
1. Composite stiffness 3,100,000(21 359)
375(101)p (21,359) (101)
Case Studies ‐ PCC
Alt tiHMA
O lUnbonded PCC
O lBonded PCCO lAlternative Overlay,
in (mm)Overlay,in (mm)
Overlay,in (mm)
1. Laboratory determined 12(305)
7(178)
4(100)1. Laboratory determined (305) (178) (100)
1. Backcalculated PCC 12(305)
7(178)
4(100)
1. Composite stiffness 12(305)
7(178)
4(100)
Case Studies – PCC ‐ Findings
• HMA overlayHMA overlay
– Varying subbase stiffness had little influence on
determined k‐value
– Stiffness of base may not be included in k‐value y
calculation (possible bug)
– MEPDG possibly ignores entered k‐value (possible
bug)g
