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Green Bay bridge Sag

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oldestguy

oldestguy

Geotechnical
Jun 6, 2006
5,183
Hi: Interesting since I think I was on board, Head getoech engineer at WiDOT, when this was being designed. I seem to recall deep soft highly plastic clay. this link may work.

National experts to help inspect sagging I-43 bridge in Green Bay*

You can get plenty more info by searching for Green Bay Press Gazette. One video there also.
 
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I don't have any knowledge of this bridge's design, but there was similar, less dramatic event on a much smaller bridge in SC several decades ago. In that case it was neither a geotechnical nor a structural problem - it was a construction related (equipment maintenance) issue:

The bridge was on pile supported piers. The contractor used a properly sized, single-acting Vulcan steam hammer to drive the piling. Turns out that a worn timing mechanism on this hammer allowed the steam (compressed air) to enter the cylinder too early - before the ram had impacted the anvil. This cushioned the impact so that no where near rated energy was delivered to the piling. The hammer "looked" to be operating normally to both the contractor and the DOT inspectors. Over time, for no apparent reason, one pier settled several inches then stopped. Why only one pier, I don't know, but that is what happened. The cause of the problem (worn hammer timing mechanism) was determined later.

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In this case the settlement is about two feet. Apparently the pile cap has a break in it also. The spokes person refers to it as a footing. Steel piles went to rock maybe 60 feet down or so, per the video info. I'm curious as to maybe steel piles corroded in an acidic soil? Two feet does not seem right for tips on rock to move. Could be pipe or H piles. With pipe, I suppose questions on concrete fill. Tips on end?
 
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I wonder if it's possible that karst conditions in the bedrock could be involved? I believe there are various limestones and dolomites in Wisconsin as I recall (similar to many parts of Michigan). Perhaps a localized (very deep) sinkhole below the piles there in that section of the bridge?

Interesting info about the other bridge with the pile hammer issue, SRE. Is there any case study paper on that particular site? I'd be interested in hearing more about that.
 
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Karst is very likely. The geology there has the sedimentary beds sloping down to the north, roughly 5 feet per mile and to the east. In the south-west part of Wisconsin, dolomite exposed is significantly weathered, leaving caves, cavities and crevices filled with soft clay. It is unpredictable as to extent. That formation is likely under Green Bay also. I'd expect a test boring is scheduled there. Per some on line bridge info, rock is 100 feet down there. You can see by this map that the light green (Sinnipee Group) is shown there (Green Bay is at the south end of the bay). See this map: Usually the only "support problem" noted on pile driving jobs to bedrock (that I know of) is uneven penetration. Two bridges settled due to artesian water flow up along the sides of timber piles, taking away frictional support.
 
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MRM - The pile hammer problem happened in the early 1950's in South Carolina. Don't know of any type documentation or paper about it. I'm aware of it more as bridge contractor's "folklore" than as an engineering problem. My father (in the bridge construction business) knew about this issue when it happened. Also, I have driven over the bridge - there is a visible dip at the one pier and you can certainly feel it in a car. Since the dip was relatively small and no corrective action was needed, it has remained a quiet example of unexpected risk a bridge contractor can face. Since highway construction projects were built with real-time inspection and acceptance of work from DOT inspectors, there was no liability for the contractor after the fact.

As for the technical details, consider a Vulcan #1 single-acting steam hammer: 5000 lb. ram falling 3', developing 15,000 ft. lb. Now, say that the ram falls 2.5', THEN steam (compressed air) is admitted prematurely and for the last 6" of fall the ram is actually decelerating. Using this simple (hypothetical) assumption the hammer's effective fall is really only 2' and actually delivers only 10,000 ft. lb. to the pile.

Using the common (at the time) Engineering News pile driving formula, you have a hammer that is expected to and appears to be developing 15,000 ft. lb. However it is ACTUALLY developing 10,000 ft. lb. When the equation is solved and the pile has been calculated to have been driven to design bearing value... it is actually at only 2/3 of design bearing value.

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I may be wrong, but doesn't the ENR formula have a safety factor of 5 or 6? Or is that for the drop hammer version?
 
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oldestguy - Yes, an "assumed" safety factor is 6 for the ENR formula for single acting hammers. The example that I offered is hypothetical, just to give a mathematical idea how the premature introduction of steam can effect hammer energy output. Perhaps the numbers for the real case were worse.

Also, recall that only one pier out of many settled... perhaps there was a "perfect storm" of poor soil, inferior hammer performance, and random load application that happened at that one spot to cause that one pier to settle - no way to tell.

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As of 2:30 today (THURSDAY) there will be a news conference. Hopefully the video will be more professional so we can hear better. The Press Gazette site is rather screwed up when it comes to playing videos. Apparently corrosion "caused the piles to buckle". A photo shows a section of an H pile. Since that is an industrial area, perhaps some highly acidic soil is present. Wiss, Janney & Elsner has been hired. While they are good, I've known them to be wrong.
 
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oldestguy - Thanks for the link. I watched and read the TV stations report. Now, have to agree that pile hammer underperformance was not an issue.

...however, I'll stick my neck out again. If the steel pile were overdriven initially then that could have initiated bucking, which has now been turned into failure by years of corrosion. I have encountered deformed piling because of overdriving.

Please note that I completely understand that all my speculation on this subject is "outside the box". Accordingly, I have confined it to BigH's private forum for consideration - not a word in any of the technical forums. As a former bridge contractor, with first-hand experience driving piling, just wanted to offer a little different view of the possible causes.

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SlideRule:

Makes sense, because the stresses in the steel are near ultimate in compression, per formulas, that doesn't mean the hammer obeys those restrictions. I also wonder about how good the cushion blocks are. News item tonite says the same soil is there now as when built, various fill with foundry sand being common. Some of the foundry sand I have run into in the past was rusty colored. Also, where are the downspout scuppers? With salt and chloride used to clear snow, it is likely that is discharged near the piers. Over the years a lot of that road maintenance chemical could have been collecting at the pile caps.

I had a tractor with chloride in the tires for weight and happened to drive over a nail. That stuff sure viciously ate up a bunch of steel I had on the garage floor nearby. Kinda brings up the question of other bridges in this north country.
 
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Looking at this shot, it seems like more corrosion that the section shown. That may be just a typical H section, not from the bridge. I'd guess that the buckle was, lets say the upper west flange went east and now is beside the lower east flange. Assuming the shot is looking south.

 
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