Influence of Subgrade/Subbase Non-Uniformity on PCC Pavement Performance

Transcription

1 Influence of Subgrade/Subbase Non-Uniformity on PCC Pavement Performance Tyson Rupnow, Ph.D. Concrete Research Engineer Louisiana Transportation Research Center David White, Ph.D. Halil Ceylan, Ph.D.

2 Outline Non-Uniformity Causes Research Plan Field Data Modeling Data Conclusions Questions Acknowledgements

3 Hwy 30 near Ames From Building Better Roads: Iowa s Contribution to Highway Engineering

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5 UNIFORMITY The Key To GOOD PAVEMENT PERFORMANCE Compliments of ACPA

6 Non-Uniform Subgrades Achieving uniform subgrade support is one of the most difficult problems facing the paving industry today

7 Causes of Non-Uniform Subgrade Expansive soils Differential frost heave and subgrade softening Variable soil type, moisture content and density Mud pumping and erosion at joints Cut/fill transitions Seasonal environmental effects Poor grading practices and QC/QA specifications

8 Research Plan 1. Generate field data (GeoGauge, Clegg, DCP, Nuc.) from 12 to 14 new subgrade construction or pavement reconstruction projects in Iowa 2. Based on the field results, developed simple finite element models (ISLAB 2000) to determine pavement responses of stress and deflection 3. Determine if relationship exists between pavement performance and subgrade nonuniformity

9 Field Data Cohesive Soils Typical Acceptance Zone: - Min. 95% γ d max - +/- 2% Opt. w% Dry Density (kg/m 3 ) % Compaction cannot be achieved for moisture higher than this (+7% of optimum) γ Z AV G S = Moisture Content (Percent Dry Weight)

10 Field Data Cohesive Soils

11 Field Data DCP Profile CBR DEPTH, in DEPTH, mm

12 Field Data Soil Type 0 Pavement Layer Base and Subbase 1 A-4 (SC) Depth from top of pavement surface, m LL PI w o A-7-6 (CH) A-4 (SC) A-7-6 (CH) A-4 (SC) A-2-4 (SM-SC) 7 A-7-6 (CH) A-4 (CL) Moisture Content and Atterberg Limits, % (based on dry weight) Swell Potential

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14 Field Conditions (a) (b) (a) Existing Non-Uniform Subgrade after Pavement Removal (b) Recompacted Uniform Subgrade Prior to Placement of New Pavement

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16 Subgrade Using Recycled Materials

17 Spatial Variability in Field Contour Contour Graph Graph for for Geoguage Clegg Impact Modulus Value Contour Graph for CBR % (DCP) (MPa) (CIV) Contour Contour Site: IA Site: Graph IA Graph for Granular Granular for Hydraulic 218 Base for % fines Dry Base Base Conductivity Construction Density passing Construction (pcf) No. 200 (cm/sec) Site: IA IA Base Site: IA 218 Base Construction Y Y Data Data Y Y Data Data X Data X Data -15 Data Data X X Data Data

18 Why Pavements Crack

19 Project Number of Test Points HWY 330 -Natural Subgrade 33 Eddyville Bypass - HFA 33 Lot S1 Natural Subgrade 18 Lot S1 After Stabilization 18 Knapp St. Natural Subgrade 51 Knapp St. New Aggregate Subbase 51 Average Dry Density (kg/m3) 1919 (2%) 1704 (2%) 1960 (3%) 1801 (3%) 1725 (9%) 1669 (4%) Average Moisture Content (%) Average Subgrade GeoGauge Modulus (MPa) Average Clegg Impact Value Average DCP-CBR (%) 11.5 (11%) 20 (52%) 6 (25%) 6 (20%) 9.5 (7%) 129 (20%) 27 (17%) 36 (17%) 8.1 (13%) 84 (16%) 22 (19%) 12(19%) 8.8 (10%) 140 (21%) 25 (18%) 19 (11%) 15.3 (22%) 14 (71%) 6 (61%) 3 (34%) 10.4 (8%) 83 (16%) 24 (13%) 23 (20%)

20 Input Parameter Values for Finite Element Models (ISLAB2000) Parameter Value Units PCC Pavement Thickness 275 mm Load Transfer Efficiency 90 % Poisson s Ratio (PCC) 0.15 PCC Modulus MPa PCC Unit Weight 2.41 g/cm 3 Tire Contact Area m 2 Number of Wheels 2 Tire Pressure 550 kpa Wheel Spacing 2438 mm Axle Load 8165 kg Winkler Springs 10-15ft In reality, the stress-strain behavior of the soil is nonlinear, irreversible, anisotropic, and inhomogeneous.

21 For the purpose of this study, the load was placed at the corner and center of each slab 18 inches from the pavement edge Load placement for PCC slabs creates a wide range of pavement responses depending upon location, subgrade characteristics and pavement type

22 Project HWY Natural Subgrade Eddyville Bypass - HFA Lot S1 Natural Subgrade Lot S1 After Stabilization Knapp St. Natural Subgrade Knapp St. New Aggregate Subbase Finite Element Modeling Results Number of Test Points Classification Average Maximum Deflection (mm) Average Maximum Principal Stress (kpa) Increase in Number of Repetitions to Failure 40 SM 0.8 (49%) 814 (29%) 40 GP-GM 0.2 (38%) 696 (10%) SC 0.2 (37%) 716 (14%) 18 SM 0.1 (36%) 687 (10%) SC 0.6 (41%) 827 (14%) 16 GW-GM 0.2 (34%) 764 (4%) 60

23 Project HWY 330 -Natural Subgrade Eddyville Bypass - HFA Lot S1 Natural Subgrade Lot S1 After Stabilization Knapp St. Natural Subgrade Knapp St. New Aggregate Subbase Influence of Uniformity Number of Loading Points Non-Uniform Average Maximum Principal Stress (kpa) Uniform Average Maximum Principal Stress (kpa) Increase in Number of Repetitions to Failure

24 Major Findings 1. Field observations and in-situ tests indicate that subgrade materials are non-uniform, which may be contributing to poor long-term pavement performance; 2. After subgrade/subbase reconstruction or stabilization, uniformity can be improved;

25 Major Findings 3. Based on the model parameters, as the modulus of subgrade reaction increases, the maximum deflection and principal stresses decrease and fatigue life increases; and 4. Benefits of uniformity of the subgrade are evidenced by the reduction of the coefficient of variation of the maximum deflection and principal pavement stresses and increases fatigue life (although not as significant as increased stiffness)

26 Acknowledgments Iowa Department of Transportation, Center for Transportation Research and Education, Fly ash Affiliates Research Program, and the Federal Highway Administration for sponsoring this study

27 More Information White, D.J., Rupnow, T.D., and Ceylan, H. Influence of Subgrade / Subbase Non-Uniformity on Pavement Performance. Geotechnical Engineering for Transportation Projects, Proceedings of Geo-Trans 2004, July 27-31, 2004, Los Angeles, California. Rupnow, Tyson. Influence of Subgrade Improvement and Non- Uniformity on Pavement Performance. M.S. Thesis, Iowa State University, Ames, White, David J., Harrington, Dale S., Ceylan, Halil, and Rupnow, Tyson. Fly Ash Stabilization for Non-Uniform Subgrade Soils, Volume II Influence of Subgrade Non-Uniformity on PCC Pavement Performance. Final Report; April, 2005.

28 Questions