Presentation on theme: "In Tai Kim & Erol Tutumluer University of Illinois, Urbana-Champaign"— Presentation transcript:
1 In Tai Kim & Erol Tutumluer University of Illinois, Urbana-Champaign Validated NAPTF Pavement P209/P154 Granular Base/Subbase Rutting PredictionsIn Tai Kim & Erol TutumluerUniversity of Illinois, Urbana-Champaign
2 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 structureCurrent standard laboratory test procedures, such as the AASHTO T307-99, not adequate for evaluating permanent deformation behavior of granular geomaterials becauseHeavier (aircraft) wheel loads appliedActual 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 rutsHighest contribution to permanent deformations often from4 to 30 inches thick P209 base, or12 to 36 inches thick P154 subbaseFAA has constructed full-scale test facility, named National Airport Pavement Test Facility, at Atlantic city, New Jersey. It allows many combinations of aircraft gear loading. First round testing of the constructed pavement test sections was completed in Two gear configurations, b777 and b 747 and up to 65,000 lbs for single wheel were applied.In Flexible pavement sections, rutting of up to 4 inches permanent deformations were observed on the surface.Furthermore, multi depth deflectometer (MDD) data and test section forensic analyses showed significant rutting was found in both P209 base and P154 subbase layersThere were 9 sections tested in first round trafficking. 6 flexible pavement and 3 rigid pavement sections. Here are the crosssections of 6 flxible test sections.6-wheel (B777) & 4-wheel (B747) Gear Assemblies
5 FAA CEAT Project Objectives Characterize Permanent Deformation Behavior Laboratory testing of FAA’s base and subbase materials, P209 and P154Develop Prediction ModelsConstant & Variable Confining Pressure (CCP & VCP) Test ConditionsInvestigate Factors Affecting Permanent Deformation AccumulationValidate Model Performances w/ NAPTF Data
6 Laboratory Investigation of Permanent Deformation Behavior 204060801000.010.1110Sieve Sizes (mm)Percent Passing (%)P154P209P209 Base MaterialFriction Angle () = 61.7Cohesion ( c) = 30 psiP154 Subbase MaterialFriction Angle () = 44Cohesion ( c) = 26.4 psiThis is the gradation curve for the P209 and p154By modified proctor test,MaterialMaximum DryDensity, kN/m3OptimumMoistureContent, %P20924.19 (154.9 pcf)4.7P15420.04 (128.3 pcf)6.5
7 FAA NAPTF Permanent Deformation Testing Program – Univ. of Illinois ► Advanced Test Equipment: UI-FastCellCompression and Extension Stress StatesConstant (CCP) & Variable (VCP) Confining Stress Paths
8 Laboratory Test Program P209 & P154 static1d (dynamic)CCP► Constant ConfiningPressure (CCP) Tests - 13Stress Ratio s1/s3 = 4Stress Ratio s1/s3 = 6Stress Ratio s1/s3 = 8Stress Ratio s1/s3 = 10s1d (kPa)s3 (kPa)62.120.796.6144.9186.3103.534.5172.5241.5310.5165.655.2276.0386.4207.069.0345.069.5Typically 10,000 load applications at each stress state
9 Variable Confining Pressure (VCP) Test Program Moving wheel loadxStressessvVertical stresstshExtensionExtensionSo far, I talked about CCP test program which didn’t consider principal stress rotation.Then, let’s move to VCP test programHorizontalstressTimeShear stresstTypical pavement elementz
10 VCP Test Program m 1d q s3d = 0 CCP Static failure VCP: s3d 0 3d VCP ( s3d & s1d )1mp = (s1d+2s3d)/3 + p0= q/3Compressionq = s1d- s3dIn general, the stress path slope for the standard constant confining pressure(CCP) tests, such as AASHTO , takes a constant value of 3.0. For variable confining pressure (VCP) tests, the stress slope varies generally from -1.5 to 3. Various stress paths cause different loading effects on pavement elements, which are not yet fully studied and understood to explain permanent deformation accumulationp0Extensionm = Dq / Dp= slope of stress path-32CCP: Constant Confining Pressure,m = 3, s3d = 0(SHRP P46)s1d = 0- q
11 Stress Path Slope (m) = -1 VCP Test Matrix – 39 testsStress Path Slope (m) = 1.5(compression states)Stress Path Slope (m) = 0Stress Path Slope (m) = -1(extension states)3(kPa)1d3d20.6772.6218.1265.4615.4361.73120.830.18108.925.63102.7168.942.24152.335.9143.6217.954.43196.446.3185.134.45201.850.43181.942.86171.5282.170.48254.259.94239.7362.390.6326.676.96307.955.12193.448.37174.341.06164.3322.680.61290.868.56274.2451112.7406.595.84383.368.9241.660.36217.751.33205.3402.9100.7363.185.57342.439 stress states were used to evaluate the effects of stress path slopes (m) and lengths (L) on the permanent deformation. Two dynamic stresses are properly applied at the same time in the horizontal and also vertical (1d) directions according to the simulated field stress states. As such, the VCP tests offer the capability to apply a wide combination of stress paths by pulsing cell pressure and vertical deviator stress.
12 Permanent Deformation (Strain) Models (based on CCP & VCP test data) f(s) Permanent Strain Models Developed in the formp = A * NBR2forAllDataR2 valuesStress Path Slope (m)m= -1VCPm = 0m = 1.5m = 3CCPP209 FAA Base MaterialCCP :p = A * 1dB * C * ND( = 33 + 1d )0.560.240.700.470.86VCP :p = A * 3B * 1dC * 3dD * NE0.800.380.780.53-P154 FAA Subbase Material0.460.620.320.850.600.35s3: Static confining pressures1d: Vertical dynamic stresss3d: Horizontal dynamic stressN: No. of load applicationsm: Stress path slopeA, B, C, D, & E: regression parametersBased on the extensive laboratory testing database established from UI-FastCell permanent deformation testing of the P209/P154 base and subbase course materials under the various constant and variable confining pressure (CCP and VCP) test conditions, seven models were developed to account for hydrostatic confining pressure (s), dynamic stresses in both axial (1d) and radial (3d) directions, stress path length (L), stress path slope (m), and number of load applications (N) as shown in Table 5–2. The model performances were compared to predict the axial permanent deformation (p) behavior of the P209 and P154 aggregates. Due to the complex loading regimes followed especially in VCP testing, models had to be analyzed simultaneously using the static and dynamic components of the applied stresses.
13 ep Model Validation w/ NAPTF Data Load WanderPatternsCalculate stressstates for eachwander position
14 ep Prediction for NAPTF Load Wander LFC P154 subbase layerp = A * 1dB * C * ND
15 ep Accumulation for NAPTF Load Sequence – 66 passes Calculate no. of load applications according to wander distributionOdd-Numbered Passes: Carriage Moves West to EastEven-Numbered Passes: Carriage Moves East to WestNormal Distribution ( s = 30.5 in.)63,6464,6661,6251,5259,6053,5457,5855,5643,4445,4641,4247,4839,4049,5037,3819,2035,3621,2233,3423,2431,3225,2629,3027,281,217,183,415,165,613,147,811,129,10Track No. :-4-3-2-112349.843 in(250 mm)typical
16 NAPTF Moving Wheel Stress Paths FAA – National Airport Pavement Test FacilityCompressionLFS sectionInterestingly, the actual stress regime experienced by pavement elements under a rolling wheel is consisting of the combination of several complex stress paths, not single stress path utilized in current laboratory test procedure, as a moving wheel is approaching and departing. Therefore, a proper laboratory test protocol is required to simulate the effect of principal stress rotation on permanent deformation development.Extension
17 ep Prediction for NAPTF Moving Gear/Wheel Loads VCP Model dp Prediction“A moving wheel loading consists of five sequential (15) load locations”Stress path slope = -14 1d = 3dStress path slope = 01d = 3dStress path slope = 33d = 0Stress path slope = 01d = 3dStress path slope = -14 1d = 3d12345The granular layer was divided into six sublayers and the permanent strain in each sublayer was computed by the model individually using the average stress states predicted at mid-depth of that sublayer, according to five different wheel positions. The predicted permanent strain in each sublayer, i.e., the summation of the strains obtained considering five load locations, was then multiplied by the thickness of that sublayer. The total granular layer permanent deformation was finally obtained as the summation of all the sublayer deformations, as explained in detail in Figure 7–12.}P154 subbase6 sublayers* Layer 1: Top layerPavement elements
18 ep Prediction for NAPTF Moving Gear/Wheel Loads Figure 7–13 shows the permanent deformations predicted from 6 sublayers using the VCP model 4. The deformations in the upper layers were usually higher than those obtained in the lower portion of the LFS P209 base layer. This is due to the fact that the upper part usually experiences higher stress states compared to the lower portion and also the prediction models were highly nonlinear stress dependent.
19 Other Major Factors Affecting Permanent Deformation Behavior Laboratory Testing versus NAPTF TestingCompacted withvibratory compactorUnconditioned virgin specimenLoaded with 0.1-sec(equivalent to 50 km/hr)load durationTrafficked at 8 km/hr (0.5-secload duration) with aircraft gearPrevious loading of baseand subbase layers duringpavement constructionand 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 effects0.5-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/h200 load cycles were applied to simulate slow moving response test for conditioning specimensStress 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 EffectsL : Load Duration EffectsMeasured Permanent DeformationVCP Prediction considering S + LVCP Prediction considering SCCP Prediction considering S + LCCP Prediction considering SLFC P154Subbase
22 SummaryConducted Laboratory Permanent Deformation Testing on the FAA’s National Airport Pavement Test Facility (NAPTF) P209/P154 Unbound Aggregate Base/Subbase MaterialsPower function form stress dependent permanent strain (ep) prediction models developed based on CCP (stationary repeated loading) & VCP (moving wheel loading) test dataRut accumulations predicted in the NAPTF LFC P154 subbase layer by properly considering load pulse duration (trafficking speed) and previous stress history effectsVCP 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 ofHeavy wheel loads: applying stresses up to 90% of the shear strengthMoving wheel loads: considering three different stress path slopes in VCP testingLoad pulse duration: in accordance with field trafficking speedPrevious stress history: preconditioning of specimensMajor AccomplishmentsPhD Dissertation of Dr. In Tai Kim– August/October 2005Final 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 appliedLoad magnitudes and loading sequences (application order and stress history effects)Trafficking speeds (load duration effects)Traffic directions (shear stress reversals)Gear spacing or interactionWander 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 potentialStudy CC3 test section subbase rutting performancesEstablish granular layer thickness/performance equivalencies
26 NAPTF trafficking dynamic response Base/SubbaseContractive &DilativeBehaviorA large scatter is observed in the permanent deformation accumulation in the P-154 subbase layer of MFC section, especially after 5,000 passes (for example, see Figure 9.24). This is due to the continual “contractive/dilative” response of the P-154 granular layer resulting from the effect of gear wander. This was pointed out in Chapter 8 while discussing the MDD transverse distribution results. This behavior is also reflected in the development of permanent deformation at the surface. Interestingly, the accumulation of permanent deformation in the subgrade shows less scatter than the granular layers even though the subgrade rutting magnitudes are higher.In Figure 9.36, the Residual or Unrecovered displacements in the pavement and subgrade layers is shown during the first 1,400 passes. The Residual responses show higher magnitudes in the pavement layers than in the subgrade. Note that the pavement layer shows a strong contractive/dilative Residual response behavior. Even though the Subgrade exhibits contractive/dilative Residual response behavior, it is mainly a contractive response. Thus, the NET permanent deformation which is equal in magnitude to the differences between the sequential dilative and contractive Residual responses will be lower in the case of the pavement layers while the cumulative contractive Residual responses produces higher rutting magnitude in the subgrade (see Figure 9.37). A closer view of the contractive/dilative Residual response behavior in the pavement and subgrade layers is shown in Figure 9.38 for one wander cycle. The maximum Residual response occurs when one of the wheel groups passes directly over the MDDs.The phenomenon of contractive/dilative permanent deformation behavior for a sequence of repetitive loads with different wander positions have been observed in previous full-scale airport flexible pavement trafficking tests (Ledbetter, 1977; Ahlvin et al, 1971; Crockford et al, 1990; Webster, 1992). Gomez-Ramirez and Thompson (2002) observed this phenomenon during the NAPTF response tests. It was also reported by Hayhoe and Garg (2002) based on their analysis of subgrade strains measured in the MFC section.