Validated NAPTF Pavement P209/P154 Granular Base/Subbase Rutting Predictions

1. Validated NAPTF PavementP209/P154 Granular Base/Subbase Rutting Predictions In Tai Kim & Erol Tutumluer University of Illinois, Urbana-Champaign

2. Introduction • Ruttingof Aggregate Layers • The only failure mechanism of Unbound Aggregate base/subbase layers – The Performance Indicator!.. • Knowledge is always required of the relative contribution of the aggregate layers to the total permanent deformation of the airport pavement structure • Current standard laboratory test procedures, such as the AASHTO T307-99, not adequate for evaluating permanent deformation behavior of granular geomaterials because • Heavier (aircraft) wheel loads applied • Actual moving wheel load conditions

3. FAA’s Full Scale Test Facility (NAPTF) • Low & Medium strength flexible sections (5 to 10 inches Asphalt & CBR 4 to 8 subgrade soils) failed with up to 4 inches ruts • Highest contribution to permanent deformations often from • 4 to 30inches thick P209 base, or • 12 to 36inches thick P154 subbase 6-wheel (B777) & 4-wheel (B747) Gear Assemblies

4. 5-in. P-401 Surface 8-in. P-209 Base 36-in. P-154 Subbase Low-Strength Subgrade LFC NAPTF Trafficking Results – LFC Wheel Load: 45,000-lbs (20.4 metric tonnes) per wheel After 20,000 passes : 65,000-lbs (29.5 metric tonnes) per wheel (Garg, 2003) http://www.airporttech.tc.faa.gov

5. FAA CEAT Project Objectives • Characterize Permanent Deformation Behavior Laboratory testing of FAA’s base and subbase materials, P209 and P154 • Develop Prediction Models Constant & Variable Confining Pressure (CCP & VCP) Test Conditions • Investigate Factors Affecting Permanent Deformation Accumulation • Validate Model Performances w/ NAPTF Data

6. 100 P154 P209 80 60 Percent Passing (%) 40 20 0 0.01 0.1 1 10 100 Sieve Sizes (mm) Laboratory Investigation of Permanent Deformation Behavior • P209 Base Material • Friction Angle () = 61.7 • Cohesion ( c) = 30 psi • P154 Subbase Material • Friction Angle () = 44 • Cohesion ( c) = 26.4 psi

7. FAA NAPTF Permanent Deformation Testing Program – Univ. of Illinois ► Advanced Test Equipment: UI-FastCell • Compression and Extension Stress States • Constant (CCP) & Variable(VCP) Confining Stress Paths

8. 1d (dynamic) static static static Laboratory Test Program P209 & P154 CCP ► Constant Confining Pressure (CCP) Tests - 13 Typically 10,000 load applications at each stress state

9. Variable Confining Pressure (VCP) Test Program Moving wheel load x Stresses sv Vertical stress t sh Extension Extension Horizontal stress Time Shear stress t Typical pavement element z

10. 1d  3d VCP: s3d 0  3d  VCP Test Program q s3d = 0 CCP Static failure 3 VCP (s3d&s1d ) 1 m p = (s1d+2s3d)/3 + p0=q/3 Compression q =s1d- s3d p0 Extension m =Dq / Dp = slope of stress path -3 2 CCP: Constant Confining Pressure, m = 3,s3d= 0 (SHRP P46) s1d= 0 - q

11. VCP Test Matrix – 39 tests

12. Permanent Deformation (Strain) Models (based on CCP &VCP test data)  f(s) s3: Static confining pressure s1d: Vertical dynamic stress s3d: Horizontal dynamic stress N: No. of load applications m: Stress path slope A, B, C, D, & E: regression parameters

13. ep Model Validation w/ NAPTF Data NAPTF Load Wander Patterns Calculate stress states for each wander position

14. epPrediction for NAPTF Load Wander LFC P154 subbase layer p = A * 1dB * C* ND

15. ep Accumulation for NAPTF Load Sequence – 66 passes Calculate no. of load applications according to wander distribution Odd-Numbered Passes: Carriage Moves West to East Even-Numbered Passes: Carriage Moves East to West Normal Distribution ( s = 30.5 in.) 63,64 64,66 61,62 51,52 59,60 53,54 57,58 55,56 43,44 45,46 41,42 47,48 39,40 49,50 37,38 19,20 35,36 21,22 33,34 23,24 31,32 25,26 29,30 27,28 1,2 17,18 3,4 15,16 5,6 13,14 7,8 11,12 9,10 Track No. : -4 -3 -2 -1 0 1 2 3 4 9.843 in (250 mm) typical

16. NAPTF Moving Wheel Stress Paths FAA – National Airport Pavement Test Facility Compression LFS section Extension

17. ep Prediction for NAPTF Moving Gear/Wheel Loads VCP Model dp Prediction “A moving wheel loading consists of five sequential (15) load locations” Stress path slope = -1 4 1d= 3d Stress path slope = 0 1d= 3d Stress path slope = 3 3d=0 Stress path slope = 0 1d= 3d Stress path slope = -1 4 1d= 3d 1 2 3 4 5 } P154 subbase 6 sublayers * Layer 1: Top layer Pavement elements

18. ep Prediction for NAPTF Moving Gear/Wheel Loads

19. Other Major Factors Affecting Permanent Deformation Behavior Laboratory Testing versus NAPTF Testing Compacted with vibratory compactor Unconditioned virgin specimen Loaded with 0.1-sec (equivalent to 50 km/hr) load duration Trafficked at 8 km/hr (0.5-sec load duration) with aircraft gear Previous loading of base and subbase layers during pavement construction and slow moving load test (response test) Load Pulse Duration and Stress History effects involved

20. Predictions Considering NAPTF Trafficking Speed & Loading Stress History Effects A new set of specimens were tested to adequately account for NAPTF (1) pulse duration (trafficking speed) and (2) stress history effects • 0.5-second load duration accumulates ~40% more permanent deformation compared to 0.1-second – viscoplastic ? • Slow Moving Response Tests with 36,000-lb wheel loads at 0.54 km/h • 200 load cycles were applied to simulate slow moving response test for conditioning specimens • Stress history ratios used in computing model parameter adjustment factors • (36,000 lbs / 45,000 lbs = 0.8)

21. Permanent Deformation Predictions Validated with NAPTF Measured Ruts S : Stress History Effects L : Load Duration Effects Measured Permanent Deformation VCP Prediction considering S + L VCP Prediction considering S CCP Prediction considering S + L CCP Prediction considering S LFC P154 Subbase

22. Summary • Conducted Laboratory Permanent Deformation Testing on the FAA’s National Airport Pavement Test Facility(NAPTF) P209/P154 Unbound Aggregate Base/Subbase Materials • Power function form stress dependentpermanent strain (ep) prediction models developed based on CCP (stationary repeated loading) & VCP(moving wheel loading) test data • Rut accumulations predicted in the NAPTF LFC P154 subbase layer by properly considering load pulse duration (trafficking speed) and previous stress history effects • VCP model predicted much closer to the measured NAPTF ruts

23. Research Findings/Accomplishments • A new granular base/subbase permanent deformation test procedure was proposed to take into account the effects of • Heavy wheel loads: applying stresses up to 90% of the shear strength • Moving wheel loads: considering three different stress path slopes in VCP testing • Load pulse duration: in accordance with field trafficking speed • Previous stress history: preconditioning of specimens Major Accomplishments • PhD Dissertation of Dr. In Tai Kim – August/October 2005 • Final Project Report – CEAT Report No. 28

24. Current/Future Research Focus • Investigate the NAPTF trafficking dynamic response database to understand complicated recovered & unrecovered pavement deformation behavior due to various combinations of applied • Load magnitudes and loading sequences (application order and stress history effects) • Trafficking speeds (load duration effects) • Traffic directions (shear stress reversals) • Gear spacing or interaction • Wander positions and wander sequences (order of 66 loadings) • Based on the proposed test procedure, fully develop a permanent deformation test procedure for evaluating airport pavement granular base/subbase layer rutting potential • Study CC3 test section subbase rutting performances • Establish granular layer thickness/performance equivalencies

25. NAPTF trafficking dynamic response unrecovered !..

26. NAPTF trafficking dynamic response Base/Subbase Contractive & Dilative Behavior

27. NAPTF trafficking dynamic response Load path (stress history) effect

28. NAPTF trafficking dynamic response NAPTF Traffic Direction Effect