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FHWA Unknown Foundations Summit
Unknown Foundations: International Survey
Jean-Louis Briaud, Dept. of Civil Engineering, Texas A&M University
Study folder if is one
Foundation inference from surrounding bridges with known foundations
Used list of participants from Inter Com Scour foundations conferences
2002 & 2005 31 responses
10 countries Poland, Singapore, Norway, Hungary, UK, Germany, Holland, Canada, USA
What tech can we use and what is accuracy?
Exists in your country?
Foundations inference—estimates based on knowledge of likely bridge construction
Ideas, but no actual practice
GPR—don't think it goes very deep, but they use it well, others should pursue
Problems—decaying of timber piles, lack of info
provided some scour prediction methods, but never worked on UF
There is conference on reusable foundations—can we reuse building foundations; it would be good to discover what they're doing.
More of a countermeasure—cover around pier, if scour happens, rip-rap fills whole
Holland said we have no problem, know what is going on.
Potentially Useful Technology
Offshore tech would be useful
Oil field technology--
Radar tech—Norway uses, go to large depths
Magnetic survey for steel piles
Homeland Security to scan for cargoes
Comments on NDE
1) Make sure to use someone with experience—be careful about misinterpreting images, use experts
2) Ask companies that make predictions not only for estimate but also probability of success—in reports don't need just the depth of pile, but also confidence level of success. Gives a sense of risk you are taking.
Comments on NDE
1) Been number of studies—do have a sense of precision with which we can rely on these techniques
Comments on Risk
Not working at a common risk of failure
Geotech are 10 times more risky than structural components, risk insurance is higher
We can decide at what risk level we want to operate
Two issues related to risk: death and economics
Comments on Risk: Human Death
How many people die per year from bridge scour failures?
Scour death 1 in 500,000 (worst year)—we are doing a good job at protecting public when comparing all other death statistics
Value of 1 human life = $1 million (US insurance average)
About 10 deaths, worst year = $10 million
Comments on Risk: Economic Loss
Risk of losing bridge due to scour in 1 year is 1 in 20,000, or 25 times higher than loss of Human life by scour
At least 22 bridges per collapsing due to scour per year
$4 million per bridge = $88 million
Risk: Economic loss
Have blue book for cars, need blue book for bridges
If I stand to lose $100,000, I don't have problem investing $10,000 for NDE
Texas DOT has started a plan of action for scour critical bridges and UF bridges Will give scour depth between 5 & 10 ft.
At this summit, lots of discussion on how solve this problem, discover foundation. Need to stop adding bridges to this list. We need to stop the bleeding.
Existing files—some bridges classified to U because DOTs too busy to do analysis
No need for more NDE analysis—it's a mature technology, but we need to think of other things
Aggressive research program worth $10 million per year
Convince Congress of importance—need civil engineers in Congress
Limit number of people who works on idea. I suggest many brains work on this.
Q: Surprised at survey response, US methodologies developed in France. No discussion of sonic echo.
JLB: You're right, but no scour problem in France.
Q: How do international governmental agencies give support, mandates, etc.?
JLB: I don't have a sense for this. Only organization is BRE in the U.K. Countries with big scour problems, UK, New Zealand, Japan. We could talk to them more.
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