Co-PIs: Erol Tutumluer Marshall R. Thompson

1. Subgrade Soil Support and Stabilization O’HARE Airport Modernization Research Project Research Progress and FY07 Tasks – January 11, 2007 Co-PIs: Erol Tutumluer Marshall R. Thompson RA: Deb Mishra

2. Introduction • The strength and performance of an airport pavement related to the structural design and the subgrade soil characteristics • This project provides testing and analysis to establish subgrade support and stabilization requirements for O’Hare airport pavements

3. Research Objectives • Consider/Establish subgrade support and stabilization requirements with respect to: • Need for subgrade stabilization • Selection of lime and other suitable admixture • stabilization considerations • Stabilization depth • Estimate “subgrade support” for various combinations of subgrade stabilization treatments and prepared subgrade conditions

4. TECHNICAL NOTES Technical Notes have been prepared and submitted to the OMP throughout the project duration to: • Establish the Best Demonstrated Available Technology (BDAT) for subgrade soil evaluation and stabilization\ • Communicate specific findings and recommendations to OMP • engineers • TN5: K-150 Considerations for RW 9-27 • TN6: Subgrade Strength/Stiffness Evaluation • TN7: “Working Platform” Requirements for Pavement Construction • TN8: Subgrade Stability Manual (IDOT) • TN13: Moisture Limitations for Lime Stabilization • TN14: Admixture Stabilization (Lime Treatment of Subgrades) • TN19: Progress Report on Laboratory Soil Test Results (3/2006) • TN 26: Evaluation of Potential Frost Problems in Pavement • Components for O’Hare Runway 9L-27R (9/2006)

5. Progress Made In 2006 • A project research paper was presented at the 2006 ASCE Airfield and Highway Pavement Specialty Conference, Atlanta, GA, April 30 – May 3, 2006 • Published in the Proceedings bookAirfield and Highway Pavements, edited by I.L. Al-Qadi “Characterizing Subgrade Soils and Establishing Treatment Needs for a New Runway at the Chicago’s O’Hare Airport” by H.S. Brar, E. Tutumluer, M.R. Thompson, L. Gosain, and R. Anderson

6. Progress Made In 2006 • On April 5th, 2006, the Co-PIs joined a TEL-CON meeting with the OMP concerning the project findings on subgrade stabilization and additional frost action effects. It was recommended that Dr. Dempsey (a participant in the TEL-CON) conduct a climatic-modelling study of the 9-27 RW • Both North Runway 9L-27R and South Airfield subgrade soil support and stabilization needs were discussed: • effectiveness of lime stabilization on primarily silty soils with low clay contents (less than 20%), • adequate strength gain requirements, • poor workmanship and inadequate construction quality control, • construction cut off dates for lime treatment effectiveness, • frost penetration effects, and • Cement treatment as an option to include in the construction specifications (and use in certain project locations in case lime treatment becomes unsatisfactory for the primarily silty, low clay contents soils to be encountered during subgrade preparation)

7. Progress Made In 2006 • Marshall Thompson traveled to the OMP office on April 11th and participated in a conference at ORD with OMP staff concerning soil stabilization (lime/cement, frost action effects, and use of fly ash as a stabilization admixture) • Erol Tutumluer gave a progress update on July 20th at the OMP office and found out that fly ash was now used for modification of the North Runway soils • Marshall Thompson traveled to the OMP office on July 28 and participated in a conference with OMP staff and 9-27 Design Staff concerning treatment options for “unstable” subgrades. He participated in the subsequent development of recommendations.

8. Progress Made In 2006 • Professor Barry Dempsey, a UIUC expert on climatic effects has completed a study of frost penetration and freeze-thaw cycle activity for the various 9-27 pavement configurations. The study considered ORD climatic data for the period 1996-2006. The report has been published as CEAT TN 26: Evaluation of Potential Frost Problems in Pavement Components for O’Hare Runway 9L-27R Conclusions from this study are as follows: • 1. The exposed lime-soil layer could experience more than 15 freeze-thaw cycles at the top, 5 to 11 cycles at mid depth, and 1 to 4 cycles at the bottom

9. Progress Made In 2006 • 2. The lime soil layer could be subjected to more than 10 freeze-thaw cycles at the top, 2 to 6 cycles at mid depth, and 1 to 3 cycles at the bottom • 3. The lime soil layer may receive 3 to 10 freeze-thaw cycles at the top, 1 to 4 cycles at mid depth, and 0 to 2 cycles at the bottom

10. Progress Made In 2006 • 4. The lime treated soil layer may receive 1 to 4 freeze-thaw cycles at the top, 0 to 3 cycles at mid depth, and 0 to 1 cycles at the bottom • 5. Lime reactivity can be expected to decrease as temperatures approach 40°F. This can be expected to occur about mid-October for an exposed lime soil layer. • 6. Significant frost penetration should be expected by mid- to late-November

11. Progress Made In 2006 • On October 4th, Ross Anderson reported on unstable soils encountered under the taxiway pavement on the South Airfield. The undercuts varied from 5 to 12 feet in depth. Asphalt Concrete (AC) millings were utilized as the compacted backfill material. Subgrade support was mainly questioned. • To accomplish k=150 pci for pavement design and subgrade support considerations (TN5), “capping” the AC millings with 8 to 10 inches of CA6 aggregate material was recommended as acceptable and not adversely impacting the uniformity of support • To place soil on top of granular backfill material to provide a “stabilized soil layer” was not recommended • The quality of the CA6 capping layer is better than the stabilized soil layer and would contribute to an improved “k”

12. Progress Made In 2006 • On November 6th, Ross Anderson forwarded cured (Qu) strength data obtained from South Airfield Shelby Tube samples (ST-8, ST-9, ST-10, and ST-11) taken from soils stabilized with 5% lime after 48 hours curing. It was encouraging to see the soils reacted favorably. Additional strength would be developed with further curing. The 48-hours @120oF is equivalent to about 28 days @70-72oF. • In Section 3.03 of P-158, the “mixture design” process is to establish the “lime reactivity” of the soil and establish proportions (3-5% lime). Although not stated in P-158, the curing conditions should be “sealed specimens” and 48 hours @ 120oF. The compressive strength requirement is 150 psi. The 150 psi requirement is for the IDOT “BASE ” mixture. The IDOT 2002 spec. compressive strength requirement for SUBBASE is 100 psi. The LIME STABILIZED SUBGRADE at OMP is utilized as a SUBBASE.

13. Progress Made In 2006 • Note in the current P-158 that Section 3.11 (Quality Control) requires the contractor to develop a QC Plan to establish: “proof of application, and to obtain depth of mixing and the required compaction” • There is no “field” compressive strength requirement in P-158. P-158 is a “process control” type specification, not an “end-result” spec based on field compressive strength. • Concerns about the “reactivity” and “suitability” of the soil for lime stabilization should be addressed prior to construction. The cured strength of the “field mixture” is of interest, but is not necessarily a desirable QA/QC tool. • The use of cured strength of “Shelby Tube” samples from field-mixed & compacted mixture as a QA/QC approach places unrealistic expectations and burdens on the contractor

14. Progress Made In 2006 • On December 20th, Ross Anderson forwarded soil data from 6 subgrade test pits (TP1 through TP6) taken on 9L-27R • TP1-6 sketches indicated areas of concern were in “fill sections” • With the exception of TP5, the Qu (pocket penetrometer) values are 4.0-4.5 tsf, which are good values • Deflecting/pumping under loaded scrapers considered as a way of “proof rolling” is not a requirement in the P-152 (Excavations and Embankments) spec.Only requirements are: • Soil shall be within +/- 2% of OMC before compaction • 90% compaction of Modified Proctor under pavement areas • UIUC staff recommended a thorough review of QA/QC compaction data for the suspect areas • The < 2-micron clay contents (do not use < 5-micron!!!) for the TP samples ranged from 12% (TP2) to 25% (TP1) • mostly AASHTO A-4 moisture susceptible silts • Group 1 & Group 2 samples utilized in the UIUC lime study (TN 19)

15. Grouping of Soils at ATREL Grouping done primarily according to % clay content!..

16. Group 1 Results Moisture-Density (Std Proctor)

17. FY 07 Year 3 Project Tasks

18. FY 07 Year 3 Project Tasks Task 1: Cooperate with OMP in the reviewing (and modifying if appropriate) Section P-152 (Excavation and Embankment) and Section P-159 (Lime Modified Soils or Fly Ash Modified Soil) specs • Experiences (problems/successes) from the current 9-27 contract should be considered • Potential use of fly ash on the South Airfield will likely require studying effectiveness of fly ash treatment in the laboratory

19. FY 07 Year 3 Project Tasks Task 2: Cooperate with OMP in the reviewing and modifying Section P-158 (Lime Stabilized Subgrade) for inclusion in the upcoming paving contract • Current version cites “latest edition” of IDOT Specs. Should reference the IDOT 2002 version • Modify Spec. (as needed) to include cement as a possible admixture • Incorporate frost action and freeze-thaw potentials from Dempsey’s study (TN 26) as guidelines • Will construction be permitted outside the current April 15 – Sept 15 window? • Additional lime testing for different temperature conditions affecting curing and strength gain?

20. FY 07 Year 3 Project Tasks Task 3: Evaluate the 9L-27R runway/taxiway soil lime stabilization and (fly ash) modification for meeting the subgrade support (k-value) requirements The research team will support the activities of OMP in: • Characterizing soils at finish grade elevation for “stabilization admixture selection” • Evaluating completed modification/stabilization effort • Field Validation of completed pavement structure

21. FY 07 Year 3 Project Tasks Task 4: Evaluate currently available geotechnical/subgrade data for the South Airfield of the O’Hare Airport with particular emphasis on the stockpiled soils • Summarize technology and experiences from North Runway (9-27) and apply to the South Airfield • Advise on the soil sampling needs and if considered essential, develop recommendations for additional soil exploration/sampling activities • Develop/conduct a laboratory testing program for soil treatment and subgrade support for the South Airfield

22. FY 07 Year 3 Project Tasks Task 4: Evaluate currently available geotechnical/subgrade data for the South Airfield of the O’Hare Airport with particular emphasis on the stockpiled soils • Summarize technology and experiences from North Runway (9-27) and apply to the South Airfield • Advise on the soil sampling needs and if considered essential, develop recommendations for additional soil exploration/sampling activities • Develop/conduct a laboratory testing program for soil treatment and subgrade support for the South Airfield

23. Project Schedule & Deliverables • 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 • 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 • Continue to work with OMP on current and future subgrade soil support and stabilization needs for all O’Hare runways/taxiways. This will be in the form of sustained support for working with OMP on subgrade soil support issues

24. Any Questions?

25. Group 1 Results

26. Group 2 Results Moisture-Density (Std Proctor)

27. 60 50 OMC = 16% 40 CBR 30 20 OMC = 14.1% 10 0 10 12 14 16 18 20 22 24 0% Lime 125 5% Lime OMC =14.1% 120 OMC=16% 115 Dry Density (pcf) 110 105 100 95 10 13 16 19 22 25 Moisture Content % Group 2 Results

28. DEMPSEY STUDY FINDINGS

32. TOTAL PVT THICKNESS – 40 INCHES

37. 9-27 PAVEMENT FROST LINE 46 INCHES

38. AVERAGE 39 INS 9-27 PAVEMENT SECTION