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 • Methodologies for Thickness Evaluation • Acquisition and Interpretation of GPR data • GPR Data Quality • Validation of Methodologies

3. Introduction • Background on Pavement Thickness Determination • 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

16. Simple GPR Thickness Model

17. EM Wave Propagation Velocity

18. Dielectric Calculation

21. Principles of GPR Interface Interpretation • 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