Sheetpile Failure 2

[Stymied]

I fess up that I am not an engineer. I own a channel lot. 70' of channel frontage. Steel sheetpile wall, clay soil, 24" by 12" sheetpile deadmen every 10 feet 18' back from wall. Two 3/4" tie rods from sheetpile wall welded to each deadman, unfortunately not threaded and bolted. Metallurgical report shows welds weakened tierods and/or deadmen, causing low cycle fatigue and failure. Sheetpile wall was noticed bowing out in early January, 2004.

February 20, 2004 a water line at the dock broke and spewed 18,000 gallons of water over an 18 to 24 hour period of time. Question 1) How does one calculate the amount of pressure or force that this amount of water would have put on the already failing wall? Question 2) Would a properly constructed seawall have been able to withstand the pressure of 18,000 gallons of water spewing behind it?

Thanks for your help.

 

[Focht3]

Yuck!

The deadmen are 1' by 2'? With two tie rods connected to each one - effectively giving the bulkhead 0.2 square feet of deadman per foot of wall?! I'd call that a Mickey Mouse setup, but I have too much respect for Mickey.

You have lots of problems; but you need the services of a competent local geotechnical engineer most of all...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[Stymied]

Sorry, misinformation provided. Deadmen are 2'wide by about 8' high. Also, your point about seeking competent engineering locally is well taken. Unfortunately, the largest and most used engineering firm in this small town is the engineer who designed the seawall.

 

[cvg]

large, and most used engineer - may translate to "cheapest"... You need an independant evaluation by a different engineer.

Seawalls should be designed to handle hydrostatic pressure from either side. After all, you are on the sea - and should expect large waves from time to time to top the wall. The wall should have also been designed with proper drainage along the back side to drain the water. The fact that a water line is installed behind the seawall is another reason that the wall should be designed for the potential leakage from the line.

 

[Stymied]

Thank you for your point. We are on a channel off of a bay in the Great Lakes...so large waves are not an issue. However, 20 years ago water levels were so high that flooding over the top of the seawall was a possibility and may again be an issue in years to come.

Stone has been backfilled behind the now pulled back wall for improved drainage. However, we are still not comfortable with tie rods welded to the deadmen, even with reinforcement on the back of the deadmen.

 

[VAD]

Can you cast concrete to encapsulte the tierods and deadman.

 

[DRC1]

First although the watermain may have put pressure on the side of the sheeting (it would depend on the size of the pipe, the water pressure and the geometry of the wall) The break probably caused severe erosion which lead to the collapse of the wall. The fact that wall began to bow noticably indicates the wall had moved ecwessively. Water mains generally do not tolerate movement well.What probably happened is the wall began to move out, causing the water main to move and probably leak. At some point the leak became a break and erroded out the soil at the toe of the wall resulting in the failure. So tanswer question no. 2 it is not hte pressure against thewall, but the erosion of the soil that was probably the culprit.
Tie rods are generally designed to pass through the deadmen and are usually bolted to a pair of channels or a beam to spread the load. This elimintes a lot of problems that can be caused by welding.

http://www.pilebuck.com

is a good website for sheeting and you can see a lot of typical details there.
Good Luck

 

[Stymied]

Thank you very much for your reply and the website reference.