1. Alaska Dept. Transportation and Public Facilities
Unknown Bridge Foundations:
Pile Length Testing and Scour Vulnerability
Alaska Dept. Transportation and Public Facilities
Hiram Henry
August, 2016

2. Scour at Unknown Bridge Foundations
Managing U-Bridges
Scour Vulnerability Evaluations
Pile Length Testing for Embedment Depth

3. Alaskan U-Bridges 1000 Publicly-travelled bridges (roughly)
50 Unknown Foundations (5 %)
Coded “U” per NBI Item #113
Scour Plan of Action required

4. Scour Estimates Joint Funding Project: USGS Alaska DOT&PF Field Survey
HEC-RAS Model
HEC-18 Scour Est.

7. Foundation Puzzle

8. Foundation Puzzle

9. Known vs. Mystery
KNOWN
Basin Hydrology
Channel Hydraulics

10. Known vs. Mystery KNOWN Basin Hydrology Channel Hydraulics
Scour Depth Estimate

11. Known vs. Mystery KNOWN Basin Hydrology Channel Hydraulics
Scour Depth Estimate
Desired Embedment Below Scour
Required Tip Elevation

12. Known vs. Mystery KNOWN MYSTERIES… Basin Hydrology Channel Hydraulics
Scour Depth Estimate
Desired Embedment
Required Tip Elevation
MYSTERIES…

13. Known vs. Mystery KNOWN MYSTERIES Pile Length Basin Hydrology
Channel Hydraulics
Scour Depth Estimate
Desired Embedment
Required Tip Elevation
MYSTERIES
Pile Length

14. Known vs. Mystery KNOWN MYSTERIES Pile Length Embedment Post-Scour
Basin Hydrology
Channel Hydraulics
Scour Depth Estimate
Desired Embedment
Required Tip Elevation
MYSTERIES
Pile Length
Embedment Post-Scour
Scour Vulnerability

15. Pile Length Testing EDAR – Effective Dispersion Analysis of Reflection
Non-Destructive Test of Pile Length
Mobile Equipment
Research by North Carolina State University, Dept. Civil Eng.
Murthy Gudatti, PE, PhD
Vivek Samu, PhD Candidate
Funded by Alaska DOT&PF and FHWA

16. Lab Development Control Pile: Length known Substrate known
EDAR test #1: Length
Seismic Testing: Pile Failure
EDAR test #2: Failure depth

17. EDAR Equipment
Accelerometers
Signal Processor
Tablet PC
Hammer

18. Old Ideal Concept Strike pile with hammer
Longitudinal Wave: Reflects from pile tip
Accelerometer: Measures reflection travel time
Length = ½ Time * Velocity
Pile

19. Reality Chaotic, Noisy Waves Must strike top of pile (inaccessible)
Multiple signals
Echoes
Resonance
Must strike top of pile (inaccessible)
Error beyond usefulness
Pile

20. EDAR Strike side of pile (exposed) Flexural wave is dispersive
Algorithms must filter and identify reflections
Error Decreased
Pile

21. Longitudinal Signal (theoretical)
time
Flexural Signal
Pile

22. EDAR

23. EDAR – Preliminary Results
Preliminary length estimate error at known piles (%):
Goal (%) +/- 10
Laboratory (%) +/- 5
Field Test (%) +/- 10
Accuracy improved with Temoshenko Beam Theory.
(Wilmington, NC Field Test)
Confidence
Level
Upper
Limit (m)
Lower
Actual
Length (m)
Limit Error (%) 95
11.56
9.31
10.85
6.57
-14.16 90
11.37
9.5
4.81
-12.38 80
11.15
9.78
2.83
-10.4

24. EDAR - Development Timeline
Theory and Laboratory
2015 – Present (North Carolina)
Field Tests and Validation – Known Piles
2016 Spring – Fall (Alaska and NC)
Implementation – Unknown Foundations
2017 Spring – Alaskan Unknown Foundations

25. Questions ?

26. Pile Types for Testing
Steel Pipe – Concrete filled (Primary For Testing)
H-Piles – Very Common
Timber – Common but Irregular Properties
Railroad Three-Rail