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Validated NAPTF Pavement P209/P154 Granular Base/Subbase Rutting Predictions In Tai Kim & Erol Tutumluer University of Illinois, Urbana-Champaign

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Introduction Rutting of 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

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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 30 inches thick P209 base, or 4 to 30 inches thick P209 base, or 12 to 36 inches thick P154 subbase 12 to 36 inches thick P154 subbase 6-wheel (B777) & 4-wheel (B747) Gear Assemblies

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Low-Strength Subgrade 5-in. P-401 Surface 8-in. P-209 Base 36-in. P-154 Subbase 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) LFC NAPTF Trafficking Results – LFC

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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

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Material Maximum Dry Density, kN/m 3 OptimumMoisture Content, % P (154.9 pcf) 4.7 P (128.3 pcf) 6.5 P209 Base Material Friction Angle ( ) = 61.7 Friction Angle ( ) = 61.7 Cohesion ( c) = 30 psi Cohesion ( c) = 30 psi P154 Subbase Material Friction Angle ( ) = 44 Friction Angle ( ) = 44 Cohesion ( c) = 26.4 psi Cohesion ( c) = 26.4 psi Sieve Sizes (mm) Percent Passing (%) P154 P209 Laboratory Investigation of Permanent Deformation Behavior

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

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Laboratory Test Program P209 & P154 ► Constant Confining Pressure (CCP) Tests - 13 Pressure (CCP) Tests - 13 CCP Stress Ratio 1 / 3 = 4 Stress Ratio 1 / 3 = 6 Stress Ratio 1 / 3 = 8 Stress Ratio 1 / 3 = 10 1d (kPa) 3 (kPa) 1d (kPa) 3 (kPa) 1d (kPa) 3 (kPa) 1d (kPa) 3 (kPa) static 1d (dynamic) Typically 10,000 load applications at each stress state

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Variable Confining Pressure (VCP) Test Program Shear stress Moving wheel load x z Typical pavement element Stresses Time vvvv hhhh Vertical stress Horizontal stress stress Extension Extension

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VCP Test Program p = ( 1d +2 3d )/3 + p 0 = /3 q = 1d - 3d m = q / p = slope of stress path CCP: Constant Confining Pressure, m = 3, 3d = 0 (SHRP P46) Compression Extension Static failure q 1 - q 3 p0p0 CCP 3d = 0 1d = VCP ( 3d & 1d ) m VCP: 3d 0 1d 3d

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VCP Test Matrix – 39 tests Stress Path Slope (m) = 1.5 (compression states) Stress Path Slope (m) = 0 Stress Path Slope (m) = -1 (extension states) 3 (kPa) 1d (kPa) 3d (kPa) 3 (kPa) 1d (kPa) 3d (kPa) 3 (kPa) 1d (kPa) 3d (kPa)

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Permanent Deformation (Strain) Models (based on CCP & VCP test data) f ( ) 3 : Static confining pressure 1d : Vertical dynamic stress 3d : Horizontal dynamic stress N: No. of load applications m: Stress path slope A, B, C, D, & E: regression parameters Permanent Strain Models Developed in the form p = A * N B R 2 forAllData R 2 values Stress Path Slope (m) m= 1 VCP m = 0 VCP m = 1.5 VCP m = 3 CCP P209 FAA Base Material CCP : p = A * 1d B * C * N D ( = 3 3 + 1d ) ( = 3 3 + 1d ) VCP : p = A * 3 B * 1d C * 3d D * N E P154 FAA Subbase Material CCP : p = A * 1d B * C * N D ( = 3 3 + 1d ) ( = 3 3 + 1d ) VCP : p = A * 3 B * 1d C * 3d D * N E

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

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LFC P154 subbase layer p = A * 1d B * C * N D p Prediction for NAPTF Load Wander

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Calculate no. of load applications according to wander distribution 1,217,183,415,169,1013,147,811,125,6 43,4445,4637,3847,4839,4049,5041,42 19,2035,3621,2233,3427,2831,3225,2629,3023,24 51,5259,6057,5855,5653,54 63,6464,6661,62 Track No. : Odd-Numbered Passes: Carriage Moves West to East Even-Numbered Passes: Carriage Moves East to West in (250 mm) typical typical Normal Distribution ( = 30.5 in.) p Accumulation for NAPTF Load Sequence – 66 passes

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

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

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Other Major Factors Affecting Permanent Deformation Behavior Laboratory Testing versus NAPTF Testing Laboratory Testing versus NAPTF Testing Compacted with vibratory compactor Unconditioned virgin specimen Loaded with 0.1-sec 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 and subbase layers during pavement construction and slow moving load test (response test) Load Pulse Duration and Stress History effects involved

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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 ? 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 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 200 load cycles were applied to simulate slow moving response test for conditioning specimens Stress history ratios used in computing model parameter adjustment factors Stress history ratios used in computing model parameter adjustment factors (36,000 lbs / 45,000 lbs = 0.8)

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

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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 dependent permanent strain ( p ) 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

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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 Heavy wheel loads: applying stresses up to 90% of the shear strength Moving wheel loads: considering three different stress path slopes in VCP testing Moving wheel loads: considering three different stress path slopes in VCP testing Load pulse duration: in accordance with field trafficking speed Load pulse duration: in accordance with field trafficking speed Previous stress history: preconditioning of specimens 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

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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) Load magnitudes and loading sequences (application order and stress history effects) Trafficking speeds (load duration effects) Trafficking speeds (load duration effects) Traffic directions (shear stress reversals) Traffic directions (shear stress reversals) Gear spacing or interaction Gear spacing or interaction Wander positions and wander sequences (order of 66 loadings) 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 Study CC3 test section subbase rutting performances Establish granular layer thickness/performance equivalencies Establish granular layer thickness/performance equivalencies

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NAPTF trafficking dynamic response unrecovered !..

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Base/Subbase Contractive & Dilative Behavior NAPTF trafficking dynamic response

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Load path (stress history) effect NAPTF trafficking dynamic response

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NAPTF Traffic Direction Effect NAPTF trafficking dynamic response

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