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Unknown Foundations

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FHWA Unknown Foundations Summit

Unknown Foundations: International Survey
Jean-Louis Briaud, Dept. of Civil Engineering, Texas A&M University

Existing Techniques
Study folder if is one
Foundation inference from surrounding bridges with known foundations
Recalculations
Risk approach
Wave propagation
Coring
Monitoring
Countermeasures

Survey list
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

2002
What tech can we use and what is accuracy?

2005
Exists in your country?
Problem?

2002 UK
Foundations inference—estimates based on knowledge of likely bridge construction
Inclined coring—

2002 Singapore
Ideas, but no actual practice

2002 Norway
GPR—don't think it goes very deep, but they use it well, others should pursue

2005 Poland
Problems—decaying of timber piles, lack of info
Solutions—

2005 UK
provided some scour prediction methods, but never worked on UF

2005 Holland

2005 UK
There is conference on reusable foundations—can we reuse building foundations; it would be good to discover what they're doing.

2005 Canada

2005 UK

2005 Germany
More of a countermeasure—cover around pier, if scour happens, rip-rap fills whole

Overall Disappointing
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
Reusable foundations
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

Future Plan
Texas DOT has started a plan of action for scour critical bridges and UF bridges Will give scour depth between 5 & 10 ft.

Future Plan
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

Future Plan
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.

Questions

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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More Information

Contacts

Silas Nichols
Office of Bridges and Structures
202-366-1554
E-mail Silas

Joe Krolak
Office of Bridges and Structures
202-366-4611
E-mail Joe

 
 
Updated: 04/07/2011
 

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