NEW GENERATION AIRCRAFT FLEXIBLE PAVEMENT DESIGN CHALLENGES M. Thompson U of IL @ Urbana-Champaign
NEW GENERATION AIRCRAFT BOEING-777 (1995) -Gross Load 632,000 lbs A380-800 800 (2006) -Gross Load 1.23 million lbs
AIRCRAFT WHEEL LOAD (KIPS) PRESSURE (psi) A-340 65.3 228 A-380 * 62 197 B-747-400ER 53.4 225 B-767-400 55.8 215 B-777-300ER * 57.9 218 B-747-400 51.1 200 * DUAL-TRIDEM
787-8 Landing Gear Footprint 74 74 FT FT 9 IN 9 IN (22.8 (22.8 M) M) 32 32 FT FT 2 IN 2 IN (9.8 (9.8 m) m) TYP TYP 38 38 FT FT 1 IN 1 IN (11.6 (11.6 M) M) Preliminary Data Data 51 51 IN IN (1.3 (1.3 M) M) CHARACTERISTI CS MAX DESIGN NOSE TAXI GEAR WEIGHT TIRE NOSE SIZE GEAR TIRE PRESSURE MAIN GEAR TIRE SIZE MAIN GEAR TIRE PRESSURE MTOW: 482 kips UNITS POUNDS KILOGRAMS IN PSI KG/CM 2 IN PSI KG/CM 2 57.5 57.5 IN IN (1.5 (1.5 M) M) 787-8 478,000 216,817 40x16.0R16/26PR MAIN GEAR TIRE LOAD: 55.5 kips MAIN GEAR TIRES: 221 psi 50X20.0R22/34PR 221 16
CBR-BASED DESIGN (COE / FAA AC No. 150/5320-6D) BASED ON ESWL Is ESWL Adequate for Dual Tandem & Dual-Tridem???
Mechanistic-Based Pavement Design Concepts for NEW GENEREATION AIRCRAFT
Mechanistic-Empirical Approach Combines the practicality of empirical methods with the technical soundness of mechanistic solutions. Uses mechanistic analysis, to determine the pavement response to imposed loads then applies empirical formulations (i.e. transfer functions ) to determine the development of distress due to the load-induced pavement response.
DESIRABLE M-E DESIGN FEATURES Technically Sound Understandable Minimum Inputs User Friendly M-E IMPLEMENTATION CONCERNS Airport Agency Resources Input Data Transfer Functions Calibration Data
Mechanistic-Empirical Approach START INPUTS Materials Characterization Pavement Materials Subgrade Soils Geometric Layout Layer thicknesses Traffic Load Levels Loading Configurations Number of repetitions Environmental Temperature fluctuations (daily, monthly) Moisture conditions STRUCTURAL MODEL Linear or Non-linear Multilayered Elastic models. OBTAIN CRITICAL RESPONSES Subgrade Deviator Stress (σ D ). Top Subgrade Vertical Strain (ε S ). Horizontal Strain (ε AC ) at the bottom of the AC layer. TRANSFER FUNCTIONS (F T ) DESIGN RELIABILITY And/Or Critical Response F T Pavement Distress (i.e. Damage) PAVEMENT PERFORMANCE Cumulative development of distress DESIGN ITERATIONS FINAL DESIGN
Mechanistic-Empirical Approach AC Layer ε AC Granular Base Layer Determine the Critical Responses Subgrade SSR = σ d / q u ε v ε AC : AC Fatigue SSR: Subgrade ε p ε v : Pavement ε p
STRUCTURAL RESPONSES * STRESSES * STRAINS * DEFLECTIONS
STRUCTURAL MODEL
STRUCTURAL MODEL SHOULD ACCOMMODATE MATERIAL PROPERTIES
Material Characterization Resilient Modulus Pavement Materials: + Asphalt Concrete: Temperature, frequency. + Unbound Granular: Stress hardening. Subgrade Soils: + Fine-grained soils: Stress softening + Granular: Stress hardening.
Material Characterization Asphalt Concrete Modulus * Temperature Dependent *Frequency Dependent * Must consider in M-E Design!!!
MONTH MMAT(F) MMPT(F)/ E (ksi) JAN 15 18/* FEB MARCH APRIL 21 28 39 25/* 33/* 46/1,870 CALGARY Temperature Data MMPT @ 3 inch depth MAY 50 58/1,045 JUNE 57 66/710 JULY 62 72/530 AUG SEPT 60 51 69/615 59/1,000 For: f=10hz * > 3,000 ksi OCT 42 49/1,620 NOV 27 32/* DEC 17 21/*
ICM NCHRP 1-37A1 ENHANCED INTEGRATED CLIMATIC MODEL (Dempsey & Larson)
HIRSCH MODEL Hirsch Model for Estimating the Modulus of In-Place Asphalt Mixtures Christensen - Pellinen - Bonaquist AAPT Journal - 2003 INPUTS VMA - VFA - Asphalt Modulus
PREDICTIVE EQUATIONS: Modified Hirsch Model 1 * 3 4,200,000 100 1 ) (1 10,000 * 3 100 1 4,200,000 * + + + = binder binder G VFA VMA VMA Pc VMA VFA G VMA Pc E 0.58 0.58 * 3 650 * 3 20 + + = VMA G VFA VMA G VFA Pc binder binder IG*I binder VMA VFA vol. properties dynamic modulus
HIRSCH MODEL + G * INPUT (TEMP / FREQ) (ASPHALT MASTER CURVE) + G * COMPATIBLE WITH PG GRADE + VFA & VMA FROM MIX DESIGN
PG 58-28 G* master curve 100000000 10000000 1000000 100000 G* (Pa) 10000 1000 master curve 100 4.4 C 21.1 C 10 37.8 C 54.5 C 1 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 Frequency (Hz)
GRANULAR MATERIALS
FROM RADA & WITCZAK
From Rada & Witczak
UZAN MODEL (1985) M R = K 1 Θ K2 (σ d ) K3 Θ =BULK STRESS Θ = σ 1 + σ 2 + σ 3
M R = K 1 Θ K2 (σ d ) K3 K1 & K2 MOST IMPORTANT!!
E Ri (ksi) = 0.307 Q U (psi) + 0.9
MODULUS CLASSES FINE-GRAINED SOILS SOIL E Ri (ksi) Qu (psi) CBR STIFF 12.3 33 8 MEDIUM 7.7 23 5 SOFT 3.0 13 2 VERY SOFT 1.0 6 1 E Ri (ksi) = 0.42 Qu (psi) - 2
ESTIMATING E Ri E Ri (OMC) = 4.46 + 0.098 (%C) + 0.119 (PI) E Ri Ri (ksi)) @ 95% T-99T C - %Clay
E CBR RELATIONS COE/FAA: E (psi) = 1,500 CBR TRL/UK : E (psi) = 2,555 CBR 0.64 (CBR: 2-12) (TRL Report # 1132) Deviator Stress =????
STRUCTURAL MODELS ELASTIC LAYER PROGRAMS FINITE ELEMENT PROGRAMS (2-D / 3-D)
ELASTIC LAYER PROGRAMS + LINEAR ELASTIC MATERIALS + MODULUS CONSTANT WITHIN THE LAYER + NO FAILURE CRITERION
Structural Models Elastic Layered Programs (ELP) All materials linear elastic, homogenous, isotropic (newer versions are improved). 2D Axi-symmetric Non-linear Finite Element: Can incorporate a wide range of material models, more specifically Stress dependent models. Results for Single Wheel Loads (in theory) 3D Non-Linear Finite Element: Same as 2D but can apply Multiple Wheel Loads.
Structural Models: ILLIPAVE Analysis for Single Wheel Load (SWL) Uses superposition to extend results to MWL. Stress dependent material models for Coarse and Fine Grained soils. Mohr-Coulomb Failure criteria. 32-bit application, run-time ~5-30 sec for typical pavement geometry. Up to 7000 elements can be used. User-friendly GUI input software for Windows.
ILLI-PAVE: 2D FEM Axis Of Revolution Surface Base Surface Base Subbase Subbase Subgrade Subgrade Results for Single Wheel Loads
Structural Models: 2D FE 3D Non-linear FEMs are very inefficient even with computing power today Consider the possibility of using 2D Non-linear FEMs with superposition to extend the single wheel results to multiple wheel. Must validate the Principle of Superposition for Engineering purposes.
ILLIPAVE MODEL * Stress dependent material models for Granular Materials and Fine Grained soils. *Mohr-Coulomb Failure Criteria. * Analysis for Single Wheel Load (SWL) * SUPERPOSITION to extend results to MWL.
MULTIPLE WHEEL SOLUTION Chou & Ledbetter (1973) MWHGL TESTS @ WES SUPERPOSITION WORKS for FLEXIBLE PAVEMENTS!!
SUPERPOSITION Studies USCOE Study 1973 (Examples ) Vertical deflection, 10-3 inches -0.05 0 0.05 0.10 0.15 0.20 0.25 0.30 0 2-0.02 0 0.02 0.04 Section #1 Section #2 0.06 0.08 4 6 8 10 0 2 Offset, FT 4 6 8 10
SUPERPOSITION Studies USCOE Study 1973 (Examples ) 80 80 Vertical Stress, lb/in 2 60 40 20 0-20 -40 0 2 60 Section #1 Section #2 40 20-20 4 6 8 10 0 2 Offset, FT 0 4 6 8 10
FAA NAPTF Study 2001 Uof IL FAA Airport Technology Transfer Conference - 2002 50.0 140.0 140.0 40.0 Vertical Stress 120.0 Vertical Stress 120.0 Vertical Stress Actual Response, psi 30.0 20.0 Rebound Response Actual Response, psi 100.0 80.0 60.0 40.0 Rebound Response Actual Response, psi 100.0 80.0 60.0 40.0 Rebound Response 10.0 20.0 20.0 0.0 0.0 10.0 20.0 30.0 40.0 50.0 Superposed Response, psi 0.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 Superposed Response, psi 0.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 Superposed Response, psi Actual Response, psi 20.0 15.0 10.0 5.0 Horizontal Stress (Radial or Tangential) Rebound Response 0.0 0.0 5.0 10.0 15.0 20.0 Superposed Response, psi Actual Response, psi 30.0 25.0 20.0 15.0 10.0 5.0 Horizontal Stress (Radial or Tangential) Rebound Response Equality Line Upper/Lower Bounds (2-psi or 10%) 0.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Superposed Response, psi Actual Response, psi 20.0 15.0 10.0 5.0 Horizontal Stress (Radial or Tangential) Rebound Response 0.0 0.0 5.0 10.0 15.0 20.0 Superposed Response, psi MFC Section HFS Section HFC Section
SOLUTION FOR MULTIPLE WHEELS ILLI-PAVE + Superposition σ σ xx yy = = ( 2 ) ( 2 σ cos α + σ sin α ) rr ( 2 ) ( 2 σ sin α + σ cos α ) rr tt tt ILLI-PAVE + Superposition σ τ τ τ zz xy yz xz = σ = = τ = τ ( σ σ ) rz rz zz rr tt sinα cosα sinα cosα Y r σ rr, σ tt, σ zz, τ rz α X
Mechanistic-Empirical Approach AC Layer ε AC Granular Base Layer Determine the Critical Responses Subgrade SSR = σ d / q u ε v ε AC : AC Fatigue SSR: Subgrade ε p ε v : Pavement ε p
CONCEPTS FOR DEVELOPING A M-E BASED ACN PROCEDURE FOR NEW GENERATION AIRCRAFT 2006 ISAP Quebec City, Canada Thompson & Gomez-Ramirez (U of IL) Gervais & Roginski (Boeing)
AIRCRAFT WHEEL LOAD (KIPS) PRESSURE (psi) A-340 65.3 228 A-380 * 62 197 B-747-400ER 53.4 225 B-767-400 55.8 215 B-777-300ER * 57.9 218 B-747-400 (REF) 51.1 200 * DUAL-TRIDEM
ICAO Subgrade "Representative" CBR Q U (psi) E Ri (ksi) A 15 68 21 B 10 45 15 C 6 27 9 D 3 14 5 ICAO SUBGRADES C = Q U /2 PHI = 0
GRANULAR LAYERS T GRAN = BASE + SUBBASE M R (psi) = 5,000 (THETA) 0.5 C = 0 PHI = 45
ICAO SUBGRADE D (CBR-3) D (CBR-3) C (CBR-6) C (CBR-6) B (CBR-10) B (CBR-10 A (CBR-15) A (CBR-15) AC (INCHES) 5 7.5 & 10 5 5 5 7.5-10 5 7.5-10 GRANULAR (INCHES) 50-100 40-100 30-70 20-70 20-60 15-60 15-50 10-50 PAVEMENT PARAMETERS
SINGLE WHEEL RESPONSES * Surface Def. (0-72 ins) * AC Surface Strain * AC Base Strain * GB Dev. Stress (top/middle) * Subgrade Dev. Stress (Top / 1&2 Radii) * Subgrade Vertical Strain (Top / 1&2 Radii)
MULTIPLE WHEEL RESPONSES (GRID: 1/4 Dual & 1/4 Axle) * Max. Surface Def. * Max. AC Surface Strain * Max. AC Base Strain * Max. GB Dev. Stress (top/middle) * Max. Subgrade Dev. Stress (Top / 1&2 Radii) * Max. Subgrade Vertical Strain (Top / 1&2 Radii)
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Deflection, mils -180-160 -140-120 -100-80 -60-40 -20 0-126 -132-152 -124-126 A340M A340B A380M A380W B747-400ER Aircraft Type -133-161 -121 B767-400 B777-300 B747-400 MLG--Surface DMax
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Deflection, mils -180-160 -140-120 -100-80 -60-40 -20 0-126 -132-152 -124-126 A340M A340B A380M A380W B747-400ER Aircraft Type -133-161 -121 B767-400 B777-300 B747-400 MLG--Surface DMax
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi 480 474 470 Microstrain 460 440 420 400 443 442 433 435 423 406 380 360 A340M A340B A380M A380W B747-400ER Aircraft Type B767-400 B777-300 B747-400 MLG--Max AC Surface Strain
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi 9.5 9 8.9 9.0 Stress, psi 8.5 8 7.5 7.6 8.2 8.0 7.8 8.5 8.2 7 6.5 A340M A340B A380M A380W B747-400ER Aircraft Type B767-400 B777-300 B747-400 MLG--Deviator Stress @ Top of Subgrade Layer
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi SSR 0.66 0.64 0.62 0.60 0.58 0.56 0.54 0.52 0.50 0.48 0.54 0.59 0.57 0.56 0.61 A340M A340B A380M A380W B747-400ER Aircraft Type 0.63 0.64 0.59 B767-400 B777-300 B747-400 MLG--Subgrade Stress Ratio (SSR)
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Microstrain -1150-1100 -1050-1000 -950-974 -1114-1057 -973-1049 -1115-1128 -998-900 -850 A340M A340B A380M A380W B747-400ER Aircraft Type B767-400 B777-300 B747-400 MLG--Vertical Strain @ Top of Subgrade Layer
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Ratio WRT B747-400 1.4 1.2 1 0.8 0.6 0.4 1.03 1.17 1.09 1.16 1.25 1.09 1.02 1.09 1.04 1.07 1.10 1.07 1.32 1.04 1.00 1.00 0.2 0 A340M A340B A380M A380W B747-400ER B767-400ER B777-300ER B747-400 Aircraft Type MLG--Surface DMax MLG--Max AC Surface Strain
ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi 1.2 1 0.93 0.98 1.00 1.12 0.98 1.06 0.95 0.98 1.03 1.05 1.08 1.12 1.10 1.13 1.00 1.00 Ratio WRT B747-400 0.8 0.6 0.4 0.2 0 A340M A340B A380M A380W B747-400ER B767-400ER B777-300ER B747-400 Aircraft Type MLG--Deviator Stress @ Top of Subgrade Layer MLG--Vertical Strain @ Top of Subgrade Layer
TRANSFER FUNCTIONS (RESPONSES DISTRESS) CRITICAL FACTORS!!!
FLEXIBLE PAVEMENT DISTRESSES HMA FATIGUE RUTTING: + HMA (MATL. SELECTION / MIX DESIGN) + GRANULAR BASE/SUBBASE + SUBGRADE
SUBGRADE TRANSFER FUNCTIONS SUBGRADE VERTICAL STRAIN SUBGRADE STRESS RATIO (SSR) (SSR= DEV STRESS / Q U)
VERTICAL STRAIN CRITERIA ε AGENCY AI SHELL 50% 85% 95% TRL/1132 (85%) ε = L (1/N) m L m 1.05*10-2 0.223 2.8*10-2 0.25 2.1*10-2 0.25 1.8*10-2 0.25 1.5*10-2 0.253 RD (INS) 0.5 0.4
WES / TOWNSEND & CHISOLM / 1976 Vicksburg BUCKSHOT CLAY (CH)
1.5 Transfer Functions: Subgrade Rutting- Vertical Strain Design Criteria VERTICAL COMPRESSIVE STRAIN AT TOP OF SUBGRADE, ε v 10-3 1.0 0.9 0.8 0.7 E S = 30,000 PSI 0.6 1,000 2,000 5,000 10,000 20,000 15,000 9,000 3,000 ANNUAL STRAIN REPETITIONS (20 YEAR LIFE) COE / FAA LEDFAA
FAA FAA SUBGRADE STRAIN CRITERIA (Revised) C = (0.004 / ε v ) 8.1 Coverages < 12,100 C = (0.002428 / ε v ) 14.21 Coverages > 12,100 C - Coverages ε v - Subgrade Vertical Compressive Strain
Transfer Functions: Subgrade Rutting-SSR Permanent Strain 0.08 0.06 0.04 0.02 0.00 Influence of SSR on Permanent Deformation 1.00 SSR Bejarano & Thompson (2001) UNSTABLE!!! 0.75 1 201 401 601 801 1001 Load Applications DuPont Clay q u = 28 psi γ d = 98 pcf w = 26 % STABLE Behavior 0.50 0.25
Transfer Functions: Subgrade Rutting-SSR p after N=1000 0.07 0.06 0.05 0.04 0.03 0.02 Permanent Deformation vs. SSR 20.0% CSSC 23.0% 24.5% 23.0% DPC 26.0% 28.5% 30.5% Bejarano & Thompson (2001) 0.01 0.00 0.00 0.25 0.50 0.75 1.00 Subgrade Stress Ratio
SUBGRADE RUTTING ALGORITHM LOG ε P = A + b (LOG N) ε P = AN b
Development of a Simplified M-E Design Procedure for Low-Volume Flexible Roads Zhao & Dennis University of Arkansas TRR # 1989 Vol. 1
Subgrade Stress Ratio (SSR) / A
Subgrade Stress Ratio (SSR) / b
Transfer Functions: Subgrade Rutting-SSR SSR General Guidelines Damage Potential Low/Acceptable Limited High SSR 0.5 / 0.6 0.6 to 0.75 > 0.75
GRANULAR LAYER RUTTING * COE NOT A CRITERION * FAA / LEDFAA - NOT A CRITERION INDIRECT ACCOMODATION: MINIMUM HMA SURFACE THICKNESS STABILIZED BASE - > 100 KIPS
GRANULAR BASE Minimum HMA Surface Thickness FAA 4-5 ins. / Critical 3-4 ins. / Noncritical (Base CBR - 80) S. African F
South African Mechanistic Approach Stress Based Safety Factor F Material Shear Strength / Shear Stress F = [σ 3 φ term + c term ] / [σ 1 - σ 3 ] where: φ term = [tan 2 (45 + φ/2) - 1] c term = 2 * C * tan(45 + φ/2) φ - friction angle, degrees C - cohesion, psi
GRANULAR BASE RATIO FOR PHI = 45 & C = 0 F = DEV. STRESS / 4.8 * SIG 3 DECREASED F : MORE RUTTING
HMA FATIGUE (TRADITIONAL)
HMA FATIGUE CRACKING
LEDFAA HMA FATIGUE LOG C = 2.68 (5*LOG ε) - (2.665*LOG E HMA ) C COVERAGES TO FAILURE ε - HMA STRAIN @ BOTTOM OF P401 HMA SURFACE E HMA HMA MODULUS (200 ksi) Heukelom & Klomp AAPT (1964)
AASHTO TP 8-94 Standard Test Method for Determination of the Fatigue Life of Compacted HMA Subjected to Repeated Flexural Bending
FATIGUE DESIGN Tensile Strain at Bottom of Asphalt Tensile Strain in Flexural Beam Test Other Configurations
FATIGUE TESTING Tensile Strain in Flexural Beam Test Other Configurations 10 Hz Haversine Load, 20 o C, Controlled Strain
STIFFNESS CURVE 8000 7000 Stiffness, mpa 6000 5000 4000 Failure 3000 FAILURE: 50% Reduction 2000 0.0E+00 5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+07 3.0E+07 3.5E+07 4.0E+07 Number of Load Cycles
LABORATORY ALGORITHM 0.01 K1 = Intercept K2 = Slope Tensile Strain 0.001 0.0001 0.00001 1.0E+02 1.0E+04 1.0E+06 1.0E+08 1.0E+10 Load Repetitions
FATIGUE ALGORITHMS N f = K1(1/ε) K2 N f = K1 (1/ε) K2 (1/E*) K3
AC FATIGUE N = K1(1/ε AC ) K2 K2 >K2 LOG ε AC K1 K2 LOG N K2 K2
HMA FATIGUE @ UIUC Carpenter - Ghuzlan - Shen
IDOT HMA FATIGUE DATA SUMMARY 84 MIXES N = K1 (1/ ε) K2 Minimum K2: 3.5 90% K2: 4.0 Average K2: 4.5
OTHER STUDIES 7 6 5 U of Illinois Maupin Results Myre FHWA Finn Linear (U of Illinois) Linear (Maupin Results) Linear (Myre) Linear (FHWA) 4 K2 3 2 1 0-16 -14-12 -10-8 -6-4 -2 0 Log(K1)
K n RELATIONS Myre / Norway NTH (1992) LOG K1 = (1.332 K2) / 0.306 U of IL / IDOT HMAs Carpenter et al LOG K1 = (1.178 K2) / 0.329
N = K1(1/HMA STRAIN) K2 HMA K2 K2 k2 K2 STRAIN 3.0 3.5 4.0 4.5 * 75 8.4 22.4 60.0 160.6 ** 150 1.1 2.0 3.8 7.1 250 0.23 0.33 0.49 0.71 * Micro-strain **Mreps
THERE IS NO UNIQUE HMA FATIGUE ALGORITHM!!!!
HMA ENDURANCE LIMIT
Monismith & McLean Technology of Thick Lift Construction: Structural Design Considerations 1972 AAPT Proceedings 70 Micro-Strain Endurance Limit!!
Michael Nunn Long-Life Flexible Pavements 8 th ISAP Conference Seattle, WA - 1997
TRL M32 CORE M32
Longitudinal crack in M1 TRL
LOW STRAIN TESTING 10000 21 Mixes Tested for Endurance Limit Flexural Strain, micro strain 1000 100 70 Micro Strain Limit 10 1.E+00 1.E+05 1.E+10 1.E+15 1.E+20 1.E+25 1.E+30 1.E+35 1.E+40 Load Repetitions, E 50
HMA FATIGUE N = K1 (1 / ε AC ) K2 ε AC (LOG) 70 µε ENDURANCE LIMIT PERPETUAL PAVEMENT N (LOG)
FATIGUE ENDURANCE LIMIT 0.01 K1 = Intercept K2 = Slope Tensile Strain 0.001 0.0001 0.00001 1.0E+02 1.0E+04 1.0E+06 1.0E+08 1.0E+10 Load Repetitions
FATIGUE ENDURANCE LIMIT Damage and Healing Concepts and Test Data Support a Strain Limit Below Which Fatigue Damage Does Not Accumulate Strain Limit Is Not The Same for All HMAs.
FATIGUE ENDURANCE LIMIT IDOT DATA NEVER < 70 micro-strain!!! GENERALLY: 70 100 micro-strain MAY BE > 100 micro-strain
EFFECT OF REST PERIODS SMALL REST PERIODS BETWEEN STRAIN REPETITIONS SIGNIFICANTLY INCREASES HMA FATIGUE LIFE IDOT HMA 5 SECONDS: 10 X
OVERLOADING HMA CAN SUSTAIN SPORADIC OVERLOADS AND RETURN TO ENDURANCE LIMIT PERFORMANCE SUBSEQUENT HMA STRAIN REPETITIONS < ENDURANCE LIMIT: DO NOT COUNT
NAPTF PAVEMENT RUTTING NAPTF TEST SECTIONS 75 FEET LONG 60 FEET WIDE
As-Built NAPTF Test Sections LFC MFC LFS MFS AC Surface (P-401) 5 in. AC Surface (P-401) 5.1 in. AC Surface (P-401) 5 in. AC Surface (P-401) 5 in. Granular Base (P-209) 7.75 in. Granular Base (P-209) 7.9 in. Asphalt Stab. Base (P-401) 4.9 in. Asphalt Stab. Base (P-401) 4.9 in. Granular Subbase (P-154) 36.4 in. Granular Subbase (P-154) 12.1 in. Granular Subbase (P-209) 29.6 in. Granular Subbase (P-209) 8.5 in. LOW Strength Subgrade MEDIUM Strength Subgrade LOW Strength Subgrade MEDIUM Strength Subgrade Subgrade=94.7 in. Subgrade=94.8 in. Subgrade=104.5 in. Subgrade=101.6 in.
NAPTF Traffic Test Program N -30 ft. -12.8 ft. B777 0 ft. Wheel Load: 45,000 lbs Tire Pressure: 188 psi Traffic Speed: 5 mph C/L 12.8 ft. B747 30 ft.
NAPTF Traffic Wander Track # -4 Track # -3 Track # -2 Track #-1 Track #0 Track #1 Track #2 Track #3 Track #4 Track # -4 Track # -3 Track # -2 Track #-1 Track #0 Track #1 Track #2 Track #3 Track #4 B777 B747 66 Passes (33 East, 33 West) σ = 30.5 in. C/L N 9.8 in. -19 ft. -12.8 ft. -7 ft. 7 ft. 12.8 ft. 19 ft. B777 WANDER AREA B747 WANDER AREA 0
NAPTF Failure Criteria At least 1 inch surface upheaval adjacent to the traffic lane (USCOE MWHGL tests) This is considered to reflect structural or shearing failure in the subgrade 1 inch surface upheaval may be accompanied by a 0.5-inch rut depth or rut depths in excess of 3 inches
High Severity Rutting
Number of Passes to Failure NAPTF Test Section 45,000-lb Wheel Load 65,000-lb Wheel Load Total MFC 12,952 * - 12,952 MFS 19,869 * - 19,869 LFC 19,950 24,145 44,095 * LFS 19,939 24,749 44,688 * * - "Failure" achieved
Max Rut Depths at Failure NAPTF Test Section RD under 45,000-lb Wheel Load (in.) RD Under 65,000-lb Wheel Load (in.) Total RD (in.) B777 B747 B777 B747 B777 B747 MFC 3.4 3.1 - - 3.4 3.1 MFS 3.5 1.0 - - 3.5 1.0 LFC 0.7 0.9 2.5 2.2 3.2 3.1 LFS 0.5 0.4 1.6 1.7 2.1 2.1
RD Vs N MFC1 Rut Depth (mils) 5,000 4,000 3,000 2,000 B777-SE B747-SE B777-TSP B747-TSP 1,000 0 0 2000 4000 6000 8000 10000 12000 14000 Number of Load Repetitions (N)
Rut Depth (mils) 5,000 4,000 3,000 2,000 RD Vs N LFC1 B777-SE B747-SE B777-TSP B747-TSP 1,000 0 0 10,000 20,000 30,000 40,000 50,000 60,000 Number of Load Repetitions (N)
Rut Depth (mils) 5,000 4,000 3,000 2,000 1,000 B777-SE B747-SE B777-TSP B747-TSP RD Vs N LFS1 0 0 10,000 20,000 30,000 40,000 50,000 60,000 Number of Load Repetitions (N)
N to Reach Specific RD Low Strength Sections Rut Depth (mils) LFC1 LFC2 LFS1 LFS2 B777 B747 B777 B747 B777 B747 B777 B747 250 28 516 28 531 10,743 12,442 28 28 500 5,008 8,083 7,791 8,723 20,068 20,642 15,111 515 1000 21,612 21,414 21,084 22,759 22,888 26,153 21,488 21,488 Medium Strength Sections Rut Depth (mils) MFC1 MFC2 MFS1 MFS2 B777 B747 B777 B747 B777 B747 B777 B747 250 28 28 28 28-28 28 5,295 500 299 133 133 133-10,529 5,373 7,513 1000 3,343 1,193 1,193 1,448-19,869 12,440 15,108
Conclusions Max RD at failure higher for conventional sections compared to stabilized sections More passes at higher wheel loads was required by L sections to reach failure compared to M sections N required by B777 and B747 gears to reach 1-inch RD were similar B777 RDs and B747 RDs do not differ significantly
M-E DESIGN TOOLS ARE: AVAILABLE AND TECHNOLOGICALLY ADEQUATE
IT IS TIME TO: MOVE ON