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Slumping WI Bridge Laid to Corrosion

Thursday, May 21, 2015

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GREEN BAY, WI—A "highly unusual environment" of fly ash, clay and bacteria bred the severe corrosion that sank part of the Leo Frigo Memorial Bridge in 2013, officials have concluded.

The four-lane bridge in Green Bay was closed to traffic Sept. 25, 2013, after drivers started calling 911 to report that a segment of the structure was sagging.

A Wisconsin Department of Transportation bridge inspector determined that a 400-foot span across all four lanes was sagging by almost two feet, the agency stated.

About a week later, WisDOT declared corrosion the likely culprit. The final investigation report, released Monday (May 18), details how several factors led to severe corrosion on one of the bridge's supporting piers.

Leo Frigo Bridge
WisDOT / Facebook

A "highly unusual environment" led to the severe corrosion that sank a section of the Leo Frigo Memorial Bridge in Green Bay in September 2013, WisDOT has concluded.

The report presents findings from the investigation and outlines the repairs and continued moniroting of the bridge. It contains two parts: the 181-page Volume I: Text, Tables and Exhibits and the 664-page Volume II: Appendices A through F.

 'Vertical Displacement'

The Leo Frigo Bridge carries Interstate 43 over the Fox River south of its mouth into Lake Michigan. About  40,000 vehicles use the bridge each day.

The structure has 51 piers, each supported by vertical steel pylons extending 100 feet underground. Pier 22  sank 22 inches on one side and 27 inches on the other.

After the bridge was closed to traffic, WisDOT inspected the underside of the bridge and found no visible signs of damage, the report said.

However, subsurface exploration that exposed sections of steel piles "determined that severe corrosion of the steel piles in the foundation that support Pier 22 was the reason for the vertical displacement," the report concluded.

Test pits were excavated at 20 of the piers, and laboratory tests were performed on soil and water samples to determine foundation conditions. Robotic survey instruments were installed to monitor any additional pier displacement.

Rapid Corrosion Factors

Several factors were found to have contributed to a "highly unusual" environment that caused the severe corrosion, the report found.

The first was the presence of a moist, porous fly ash fill with high levels of chlorides and sulfides combined with a low resistivity, investigators said.

Below the fly ash lay a dense layer of clay, leading to differential oxygen concentration and differential chemical concentrations within the fill layers. Bacteria was also found at many of the piers, and it is likely that microbiologically influenced corrosion also played a role, according to the report.

WisDOT bridge inspection
WisDOT Inspection Report

Corrosion on Pier 22 caused it to sink 22 inches on one side and 27 inches on the other.

The likely culprit for the deterioration in the failure zone was an aggressive corrosion mechanism of differential oxygen concentration corrosion in the form of Accelerated Low Water Corrosion, the report found.

These site conditions led to the rapid corrosion of sections of steel piles, and severe deterioration and crushing/buckling was observed on all piles that were exposed.

Tier-Based Repairs

In order to return the bridge to service, temporary shoring towers and new, supplemental permanent foundation elements were installed.

Bridge piers were grouped into three tiers:

  • Tier 1: Locations where immediate repairs were necessary to return the bridge to service;
  • Tier 2: Locations where much lower levels of pile corrosion damage were observed; and
  • Tier 3: Locations with low potention for severe pile corrosion.

Repairs were warranted based on tier level.

Tier 1 pier repairs included installing new concrete drilled shaft foundations. These were connected to the existing piers and provided corrosion protection measures designed to offer 75 years of service life.

Leo Frigo piers
WisDOT Inspection Report

WisDOT triaged pier repairs using a three-level system.

Tier 2 piers had monitoring probes and steel coupons installed in 2014. Data will be collected from the probes during typical bi-annual bridge maintenance inspections, the report said. Probe data will be supplemented by section loss measurements.

Since Tier 3 piers indicated pile conditions typical for the bridge's age in normal soils, no further investigation was required.

75 Years of Service

The bridge reopened Jan. 5, 2014. Cost for the entire project—from investigation to final repairs—was $15 million, according to WisDOT.

WisDOT originally estimated the cost of repairs at $50 million. According to the agency, the new repairs will offer 75 years of service life.

The Leo Frigo bridge was constructed in 1980, with repairs on the superstructure completed in 1988. The bridge was last inspected in October 2012 and was not on the state's list of 60 deficient bridges, according to WisDOT.

In 2012 and 2013, the bridge underwent asphalt, joint and pin replacement.

Formerly called the Tower Drive Bridge, the structure was renamed the Leo Frigo Memorial Bridge in 2002 in recognition of a Green Bay civic and philanthropic leader whose legacy includes one of the largest food pantry programs in the nation.

   

Tagged categories: Bridge Piles; Bridges; Corrosion; Department of Transportation (DOT); Inspection; North America; Program/Project Management

Comment from luiz de miranda, (5/21/2015, 2:27 AM)

did cathodic protection installed on the piers?


Comment from David Zuskin, (5/21/2015, 10:52 AM)

Welcome to the world of splash zone corrosion


Comment from M. Halliwell, (5/22/2015, 10:43 AM)

David, with this being a pile failure, I don't think splash zone quite applies. Fly ash fill is not a fun one to begin with....lots of heavy metals and potential for some ions that aid in corrosion. Add water and steel piles...well, as evidenced, it's not a good mix. Sacrificial cathodic protection may have helped, but with 20/20 hindsight, I'd probably say a different pile type would have been a better idea.


Comment from luiz de miranda, (5/26/2015, 8:12 AM)

I would claim for impressed current and not sacrificial cathodic protection


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