Pavement Thickness Evaluation Using Ground Penetrating Radar

1. Pavement Thickness Evaluation Using Ground Penetrating Radar Dwayne Harris P.E. L.P.G Presented for Final Exam

2. OUTLINE • Introduction • Fundamentals of GPR • Interpretation of GPR data • Methodologies for Thickness Evaluation • GPR Data Quality • Validation of Methodologies

3. Introduction • Background on pavement thickness evaluation • Literature review

4. Why Use GPR? • Why is pavement thickness information useful? • What are the current methods for obtaining thickness information? • What are the advantages of using GPR for thickness evaluation?

5. Importance of Thickness Information • Pavement management • Pavement performance and remaining life estimates require knowledge of pavement thickness • Setting maintenance and rehabilitation priorities • Main input in overlay design

6. National Rehabilitation [Hartegen, 2005]

7. INDOT • INDOT Major Moves $138,483,477 budgeted for 2006 resurfacing • Large percentage Mill and Fill rehabilitation where thickness of uppermost surface course important • Pavement thickness is needed for project level FWD structural analysis

8. Technologies Used for Pavement Thickness Evaluation • Core • Costly • Destructive • Provides a good ground truth record. • Falling Weight Deflectometer (FWD) • None Destructive • Ground Penetrating Radar • Non Destructive • Collected at Highway Speed • Dense Coverage • Heavy Post Processing

9. Related Work Thickness Evaluation • [Berge et al, 1986] initial pavement thickness studies • [Livneh and Siddiqui, 1992] mathematical model presented • [Fernando, 2000; Scullion and Saarenketo, 2002] automated interface identification • [Al-Quadi et al, 2005] model expanded to three or more layers

10. Literature Summary • There are multiple models available for pavement thickness evaluation • The model selected for this study is utilized for a large majority of the studies • Current literature suggests using semi-automatic data interpretation methodologies

11. Fundamentals • GPR trace and waveforms and data presentations • Mathematical model

14. GPR Data B-scan

18. Simple GPR Thickness Model

19. EM Wave Propagation Velocity

20. Dielectric Calculation

21. Principles of GPR Interface Interpretation An interface is defined as the anomaly in GPR data occurring when the reflected waveforms from a physical pavement boundary are contiguous for a group of sequential traces • The radar (EM) wave must propagate, to the interface and back. • The radar wave must reflect off the interface with enough energy to be recorded. • The interface must be identified in the GPR record.

23. Two Interface Case A

24. Two Interface Case B

25. Methodologies for Thickness Evaluation • Top layer methodology • Interfaces are identified in the data • Discontinuities are located in the data • Regional dielectric constants are determined • Thickness values are calculated for each mile • Enhanced to calculate thickness using dielectric constants from individual traces • Multiple Layer Methodology

26. Interface Selection

27. Regional Dielectric Constants

28. Thickness Calculation • Every thickness pick is assigned the respective regional dielectric value. • New Thickness Values Calculated. • Average value calculated for each mile.

29. Multiple Layer Methodology • Determine the layers to be modeled • Form data set of possible interfaces • Select interfaces to be modeled • Calculate thickness values • Present the thicknesses in a visually acute format allowing for proper interpretation

32. Quality of GPR Data • Blunders • Improper waveform selection • Omitted pavement layers • Systematic errors • Travel time systematic error • Velocity systematic error • Random errors • Error propagation

33. I65 Study Area

34. 13 Inches HMA Over PCC

35. TERRA Interface Selection

38. Difference in Dielectric Constant and Thickness

39. Blunders • Improper waveform selection • Omitted pavement layers

41. Omitted Pavement Layers

42. Blunder Summary • Improperly selecting waveforms is a significant blunder source • Utilizing automated interface selection algorithm increased the likelihood of this blunder • Blunders are introduced when using the top layer methodology to evaluate thickness of pavement composed of multiple layers

43. Systematic Error: Travel Time

46. Velocity Systematic Error

47. Random Error Propagation

48. Random Error Propagation

49. Systematic and Random Error Summary • Channel 1 data not used due to large systematic error is travel time • Velocity systematic errors propagate into thickness error • Amplitude random error propagates to about 1% relative thickness error

50. Validation of Methodologies • Comparison with 3rd party Software • Comparison of methodologies developed • Thickness variation • GPR thickness evaluation accuracy • Network thickness study