Subgrade Soil Support and Stabilization O HARE Airport Modernization

Subgrade Soil Support and Stabilization O’HARE Airport Modernization Research Project Co-PIs: Erol Tutumluer Marshall R. Thompson RA: H. S. Brar

Introduction ü Subgrade performance is a key factor in the overall pavement performance P 209 P 154 National Airport Pavement Test Facility Atlantic City, NJ ü This project provides testing and analysis to establish subgrade support and stabilization requirements for O’Hare airport pavements

Introduction (cont’d) ü The preliminary concrete pavement design for the O’Hare Modernization Program (OMP): • • • 15 – 17 inches of PCC Surface 6 -inch Hot Mix Asphalt Base 6 -inch Asphalt Treated Permeable Base “Stabilized” Subgrade Zone (SSZ) Prepared Subgrade ü North Runway (9 -27) paving is scheduled first for the Spring 2006 • Stockpiles of local soil on runway centerline (excavated from the “Deep Pond” nearby) • Primarily fill and cut areas

Research Objectives ü Consider pavement design inputs for subgrade support • Modulus of subgrade reaction, k ü Consider subgrade support and stabilization requirements with respect to: • • • Need for subgrade stabilization Stabilization admixture(s) stabilization Stabilization depth ü Estimate “subgrade support” for various combinations of subgrade stabilization treatments and prepared subgrade conditions

Project Tasks Task 1: Establish the Best Demonstrated Available Technology (BDAT) for subgrade soil evaluation and stabilization Reports and publications collected & submitted as “Technical Notes” on: • • • Subgrade strength/stiffness evaluation techniques Subgrade stability requirements & IDOT Manual “Working platform” requirements for pavement construction

Project Tasks Task 2: Evaluate currently available data for the subgrade test sections constructed in the Fall of 2003 and the necessity/usefulness of constructing additional subgrade treatment test sections at O’Hare Plate load tests conducted (8/04) on the test sections: • Plate 1: 12 -inch stabilization/compaction – no admixture • Plate 2: 12 -inch quicklime fine (40 lb/yd 2) & fly ash (80 lb/yd 2) stabilization • Plate 3: 12 -inch quicklime fine stabilization (40 lb/yd 2) • Plate 4: 12 -inch lime kiln dust stabilization (40 lb/yd 2)

Plate Load Tests Modulus of Subgrade Reaction, k

Project Tasks Task 3: Advise OMP on current and future test section monitoring and field test evaluation programs Various field tests may be useful to characterize the treated subgrade (OMP will arrange for testing): • • Dynamic Cone Penetrometer (8/04) Light-Weight Deflectometer (8/04) Clegg Hammer Geogauge Heavy Weight Deflectometer (HWD) Ground Penetrating Radar (GPR) Seismic Pavement Analyzer, SASW, etc.

Dynamic Cone Penetrometer Light-Weight Deflectometer

Project Tasks Task 4: Evaluate currently available geotechnical/subgrade data for the North Runway with emphasis on the stockpiled “Deep Pond” soils. Recommend further soil sampling & testing to be conducted (by an OMP designated testing firm) Routine tests to establish representative soils existing for the runway subgrade • • • Grain size distribution (including hydrometer) Atterberg limits (LL and PL for PI) Moisture-density-CBR PH value & calcareous content If needed, organic matter content

Project Tasks Task 5: Based on the data and information gathered in Task 4, select (in consultation with OMP) the identified representative soils and recommend an admixture stabilization program Non-routine testing to be conducted at the UIUC Advanced Transportation Research and Engineering Laboratory (ATREL) on both untreated & treated soils Triaxial testing for • • • Shear strength Resilient modulus Permanent deformation

Project Challenges ü Properly sampling the “Deep Pond” stockpiled soils ü Selecting & identifying representative soil samples ü Adequately characterizing the representative soil samples by conducting non-routine tests at the UIUC ATREL for • Shear strength • Resilient modulus • Permanent deformation

Project Deliverables ü Technical Notes will be prepared and submitted to the OMP throughout the duration of this project to communicate specific findings and recommendations to OMP engineers as needed ü A Final Report will be prepared at the end of the one -year study ü Several of the Project Tasks are already pursued simultaneously, and the specific delivery of results will be contingent upon availability of OMP data and other factors that depend on coordination with OMP

Advanced Transportation Research & Engineering Laboratory (ATREL) University of Illinois:

Mechanical Behavior of Subgrade Soils ü Strength: Maximum level of stress soil can sustain before it fails or excessively deforms Shear strength, tmax = c + normal*tanf c: cohesion & f: internal friction angle ü Stiffness: Stress obtained for a unit strain Resilient (MR) modulus, Poisson’s ratio (n) ü Resistance to Permanent Deformation: Ability to resist a large number of load cycles without accumulating excessive deformations dp = f(N, confinement, cyclic or t, t/tmax)

Sample Preparation - Compaction Improve strength, reduce deformation, and prepare specimens close to field construction conditions (OMC: Optimum moisture content) Laboratory Compaction Methods ü Static – Standard for soils (AASHTO T-307 -99), typically 5 layers ü Impact – Proctor type (AASHTO T-99/180), several layers ü Vibratory – Typically used for granular materials Ø Vibration in several layers (vibratory hammer)

Moisture-Density Relationship Std & Modified Proctor Compaction (ASTM D 698, D 1557) Dry Unit Weight (pcf) 130 126 gdmax 122 118 114 wopt 110 5 6 7 8 9 10 11 12 13 Gravimetric Moisture Content (%) 14 15

Typical Moisture-Density Results 120 Dry Density, pcf 115 Dupont Clay 100 % Sr (Gs = 2. 71) 90 % Sr 110 105 100 95 ASTM D-1557 90 Intermediate ASTM D-698 85 10 14 18 22 26 30 Moisture Content, % 34

STRENGTH BEHAVIOR

AC Load stress distribution Base Subgrade v = + = 1 c d c c = Confining stress = 3 d = Deviator stress = v - c v = Vertical stress = c + d Triaxial Conditions/Tests

Triaxial Testing Equipment - Capabilities Test requires: • Pneumatic to servohydraulic loading • Data acquisition system with feedback control • Personal computer with an integrated software package • Modern equipment, good technician, careful equipment calibration!. . Monotonic/Cyclic Axial Load (haversine load shape) 1 Constant/Variable Cell Pressure (air or liquid) 3 Axial Strain Measurement Radial Strain Measurement Cylindrical Specimen

Strength Tests Using Triaxial Setup • Cohesive Soils (c, f=0) – – Modified Proctor Procedure A (ASTM D 1557) Unconfined Compression (ASTM D 2166) d = 1 – 3(=0) failure C = ( 1 f)/2 = Qu/2 3 = 0 1 1 f • Sandy Soils (c, f) – Modified Proctor Procedure C (ASTM D 1557) – Rapid Triaxial Shear (UI Procedure)

Typical Unconfined Stress-Strain Data 60 Dupont Clay MC = 23 % DD = 103. 5 pcf CBR = 14 Axial Stress, psi 50 40 Qu = unconfined compressive strength = peak 1 MC = 26 % DD = 98 pcf CBR = 8 30 MC = 28. 5 % DD = 93. 5 pcf CBR = 4 20 10 0 MC = 30. 5 % DD = 92. 5 pcf CBR = 2. 5 0 5 10 Axial Strain, % 15

Strength Testing UI Rapid Shear: 12. 5%/second tmax = c + n*tanf C L Slow, monotonic 1%/minute 3 d 3 3 d = deviator FAA NAPTF P 209 Aggregate at 3 3 levels 6. 9 k. Pa = 1 psi stress 3 = cell pressure

MODULUS BEHAVIOR

Elastic (Resilient) Behavior Due To Repeated/Cyclic Load Application C L Elastic (Resilient) Modulus, E (MR ) Poisson’s ratio, n Deformation MR = d / r Recoverable Deformation d 3 3 3 MR = Resilient modulus d = Repeated wheel load stress r = Recoverable (rebound) strain Permanent Deformation Time

Resilient Modulus – Overview • Resilient Modulus (MR) is a fundamental material property – Simulates repeated application of wheel loads • MR testing is a rational test and is an improvement over CBR • MR considers fundamental effects: – Stress condition, density, grading, fines, water content • Evaluates rutting - very important

Determining Resilient Modulus • Lab Testing: AASHTO T 307 -99 (SHRP TP 46) – Undisturbed – Disturbed, remolded and compacted – Input to mechanistic based pavement design procedures • Estimate from various procedures – – Backcalculation from field FWD deflections Soil properties Unconfined compressive strength CBR

Resilient Modulus Test (AAHSTO T 307 -99) Type I: Unbound granular base and subbase materials Type II: Untreated subgrade soils, A-4, A-5, A-6, A-7 • Repeatedly applied loads – Similar to those from wheel loads • Relates to elastic component of response only – Resilient (= recoverable) deformation

Repeated Load Triaxial Test Stress States Total Axial Stress, 1 (major principal stress) M R = d / r 0 1 - 3 = Repeated (Cyclic) Deviator Stress 3 = d Shear Stresses 0 3 = Confining Pressure (minor principal stress) 2 = 3 Bulk Stress: = 1 + 2 + 3 = d + 3 3 Vertical Specimen Deformations Measured Only!. .

MR Tests – Type II Soil Samples Cylindrical specimens, 2 in. f by 4 in. high Undisturbed soil samples – Shelby tube (f = 2. 8, 4 in. )

Stress Sequence – Type II Soils • Haversine load waveform (pulse load duration: 0. 1 sec. , 5 Hz) • Conditioning: 1000 load applications at 3 = 41 k. Pa & d = 28 k. Pa ( 1 / 3 = 1. 7 only!. . ) • Testing: 100 load applications at 15 following stress states: 3 (k. Pa) 41 21 141 282 d 413 (k. Pa) 554 695 0 146 1411 287 2812 418 4113 559 5514 6910 6915 d 3 AASHTO T 307 -99 - SHRP Protocol P 46 1: testing sequence number 3 3

Subgrade Deviator Stress P Wheel AC Aggregate Subgrade soil d 3 = low !. .

University of Illinois MR Testing Procedure - Type II Soils • Haversine load waveform (pulse load duration: 0. 1 sec. , 5 Hz) • Conditioning: 200 load applications at 3 = 0, d = 41 k. Pa • Testing: 100 load applications at 8 following stress states: sd = Repeated Deviator Stress Unconfined: s 3 = 0 d = 14, 28, 41, 55, 69, & also 83, 96, 110 k. Pa 2 -in. in f d

University of Illinois – Repeated Load Triaxial Test System

Factors Affecting MR of Type II Soils Fine-grained subgrade soils: silts and clays Primary Factor • Applied stress states, d and 3 Secondary Factors – soil properties • Moisture content, w (or Saturation, SR, %) – Suction = f(depth to groundwater table) • • Plasticity index, PI Clay content, % (smaller than 2 mm) Dry density, gd Freeze-thaw effects

Stress Dependent MR Behavior Nonlinear stress dependent behavior – Stress softening (fine-grained soils) – Stress hardening (coarse-grained, aggregates) cohesive soils MR = f ( ) linear elastic aggregates ep e

Arithmetic or Bilinear Model Cohesive Soils: MR = f( d ), Mainly Shear Stress Typical Fine-Grained Soil Stress Softening Behavior + K ( K - ) when < K d 2 R 1 3 2 d • M = K - K ( - K ) when > K R d 2 1 4 d 2 • M =K R MR 1 where d = 1 - 3 K 2 K 1 1 K 4 d Thompson and Robnett (1979) K 1 = Eri = Breakpoint modulus K 2 = db = Breakpoint deviator stress = (2~6 psi)

Typical MR Characterization for Soils Greensboro, NC Airport Subgrade Soils 28 M R = - 2. 21248 d + 29. 696 2 R = 0. 9497 RESILIENT MODULUS M R (ksi) 24 A-4 soil at OMC+3 20 Bilinear or Arithmetic Model 16 M R= - 0. 6274 d + 1820 2 R = 0. 6617 12 8 4 M R= - 0. 4203 d + 8. 351 M R = 0. 0408 d + 4. 9412 2 R = 0. 8715 2 R = 0. 8796 0 0 2 4 6 8 10 12 14 APPLIED DEVIATOR STRESS d (psi) 16 18

Empirical MR - CBR Correlations MR (psi) = 1500 * CBR (Heukelom and Klomp, 1962) MR (psi) = 2555 * CBR 0. 64 (2002 Design Guide Prepared for AASHTO) Limited application for up to CBR = 10 -12

Empirical MR - CBR Correlations The empirical correlations may not always work !. . Greensboro, NC Airport Subgrade Soils

PERMANENT DEFORMATION BEHAVIOR

Permanent Deformation – Rutting Permanent Deformation PRIMARY PERFORMANCE INDICATOR Base/Subbase Materials and Subgrade Soils Wheel Rutting!. . Load Repetitions Permanent Deformation: dp

Permanent Deformation Testing Ø Much less advanced than resilient behavior Ø No well-established test procedure exists Ø Yet, soil performance is solely judged by its field permanent deformation or rutting potential Ø Cohesive Soils – U of I procedure Ø Stress Levels: 25, 50, 75 & 100% of Qu Ø Subgrade Stress Ratio (SSR) = D/Qu Ø N = 1000 (Conditioning) up to 100, 000 Ø For a given stress level Ø Permanent strain (ep) is monitored Ø ep versus N plots for various stress levels

Typical dp Test Results - Soils Permanent Strain, ep 0. 10 Dupont Clay 0. 08 qu = 28 psi gd = 98 pcf w = 26 % 1. 00 SSR 0. 06 0. 04 0. 75 0. 02 0. 50 0. 00 0. 25 1 10 100 No. of Load Applications 1000

Typical dp Test Results - Soils Perm. Strain after N=1000 0. 07 0. 06 moisture contents 0. 05 26. 0% 0. 04 Dupont Clay 23. 0% 28. 5% 30. 5% 0. 03 0. 02 0. 01 0. 00 0. 25 0. 50 0. 75 Subgrade Stress Ratio 1. 00

Factors Affecting Permanent Deformation dp of Soils Primary Factors • Applied stress states, d, 3, and strength (Qu or max) – Subgrade Stress Ratio, SSR ( = d / Qu) • Number of Load cycles, N Secondary Factors – soil properties • Moisture content, w (or Saturation, SR, %) – Suction = f(depth to groundwater table) • Plasticity index, PI and clay content, % (<2 mm) • Dry density, gd • Freeze-thaw effects

Permanent Deformation - Power Model Permanent Strain, ep 0. 1 moisture contents 23. 00% 26. 00% 28. 50% 30. 50% Dupont Clay 0. 01 0. 001 1 p=ANB 10 100 No. of Load Applications 1000

Permanent Deformation - Power Model 1. E-03 Permanent Strain, ep Sand e p = 1. 4 x 10 -4 N 0. 137 1. E-04 1. E-05 2 R = 0. 96 d = 45 psi 3 = 15 psi 1 10 100 No. of Load Applications 1000

Thank you for the Excellent Pavement !. .