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

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

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

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

Foundation Puzzle

Foundation Puzzle

Known vs. Mystery KNOWN Basin Hydrology Channel Hydraulics

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

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

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

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

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

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

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

EDAR Equipment Accelerometers Signal Processor Tablet PC Hammer

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

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

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

Longitudinal Signal (theoretical) time Flexural Signal Pile

EDAR

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

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

Questions ?

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