Support a leaning Steel Sheet Pile

[srw2104]

Hello all,

I am currently working on a project which entails the following:

There is a steel fence which is welded to steel sheet pile which is slowly beginning to collapse; much similar to that of the "Leaning Tower of Pisa". The sheet pile is driven 12 feet into the ground and the fence is roughly 8 feet tall. The problem is that the steel sheet pile which runs along side a lake is beginning to bow outwards towards the lake. The sheet pile is not buckling but it is simply leaning. I need a temporary solution to this problem. Temporary being around a year and a half until a permanant solution takes place. I am wondering if there is anything someone can do to help me out with this issue. Any advice is greatly appreciated, whether it be formulas I should use for load calculations, stress, strain, etc...or better yet, even an idea as to how I could stablize the fence back to its original straight up position.

Thank you so much in advance!

 

[DickL]

This is more of a civil engineering problem, but there isn't a CE section here.

It sounds to me as though there is Earth movement, toward the lake, that is moving the sheet piling. If the lake is deeper than 12 feet somewhat close to the piling, I suspect there isn't a lot you will be able to do to hold that piling in place. You may be able to tie it back to more solid ground with cables and Earth anchors, or replace the piling with ones that are driven deeper.

Do you have geotech information on the site. That may give you some ideas, or allow you to consult with the geotechs.

This is getting way beyond my ME and assorted other background.

 

[Studiot]

Hello srw2104 and welcome to Physics Forums.

This is getting way beyond my ME and assorted other background

Maybe, but is was still a pretty good summing up IHMO.

Just to clarify.

Is the top of the pile leaning over downhill into the lake?

If so that would suggest the pile itself is bending, but remains firmly anchored at depth.

In this case tying the top back to another anchor at least twice the depth of the pile behind the pile would work.

If it is leaning upslope - away from the lake then the ground at depth is moving towards the lake, taking the toe (bottom) of the pile with it.
In this case there is nothing you can do except drive the pile in further (or another one) and hope.

go well

 

[srw2104]

Thank you both very much for the quick reply...I will attempt to address all of your questions.

DickL:

I feel as if you are right about the Earth movement which is causing the problem. It seems as if the soil is just too weak near the lake and the weight of all the material is causing it to lean. I do not have any geotech information at this time...but I do in fact plan to bring in someone to obtain that information.

Studiot:

Essentially, the fence is at about a 10 degree angle pointing out towards the lake. You may be correct in that the sheet pile is bending at a point lower than I can see..but I am almost certain this is not the case.

I want to anchor the sheet pile with Earth anchors and steel rope...but I am questioning if this will work for such a long period of time.

 

[Studiot]

Tying back the top may hold it for your year. Since it is tilting at the top it has either rotated or bent. So the bottom has not (yet) moved forward. Perhaps the ground in front of the pile has slumped towards the lake?

It rather depends upon how long the existing movement has taken.

If the pile has suddenly tilted probably not, if the movement has taken considerable time probably so.

When you reconstruct, with perhaps gabions, remember to found at a sufficiently low level. Those who do not found retaining structires alongside water low enough invariably find their structure ending up in the water.

go well

 

[srw2104]

Do you possibly know of any formulas or calculations I can perform in order to see how much force really is pulling this fence down?

 

[Studiot]

Not without a great deal more information.

How about a dimensioned cross section?

 

[srw2104]

I will absolutely provide that at a later time. I have to go down there and make measurements. I will post a sketch of it next week sometime as I will be going out of town. In addition...I really do appreciate all the help. Thank you very much

 

[Studiot]

Something to indicate the shape of the lake side will be needed ie how steep is the bank?

 

[Studiot]

Some ideas about what might be useful contributory information.

 

[srw2104]

studiot, you are excellent help. I couldn't thank you enough. Currently I am trying to upload a sketch I made which will allow you to visualize what I am talking about but for some odd reason It will not work for me although I have never had trouble doing it in the past.

 

[Studiot]

Further question.

What is known about the groundwater in the area?

Are there any sewers, road drains, land drains (including slit trenches) or other pipes than may be blocked or damaged?

Are there any springs on the slope above the level of the pile?

 

[srw2104]

Here is a photo taken of the fence I have described. A sketch of the area will be attached as well

 

[srw2104]

Here is the supplemental sketch...thanks again!

 

[Studiot]

Thanks for the pictures, the situation is fairly clear.

In the picture you can see where the ground has slumped to a trench or furrow behind the displaced piles. This shows as a brown gash in the green turf.

Almost certainly, the water has undercut these piles so pulling the tops back will be counterproductive in that the whole zone may give way.

Are you sure there is no pipe entering the water beneath these piles?

You say they are only baby piles (12ft long). Your best bet would be to get a JCB and push them in further with the bucket, welding extensions on the top if necessary. This would be a quick and cheap operation and not leave any dangerous anchor cables at the surface.

Are the white rails bike stands?

 

[srw2104]

thanks studiot...do you think another option may be to use a backhoe to dig out the area of soil directly in front of the sheet pile in order to relieve some stress on the pile. Thank using eye hooks and concrete footings, implement a chain and "come a long" to pull the sheet pile back. I think it may be too diffiicult to set it back into a straight position...but this may hold it for the 18 months until a permanant solution. What do you think? Also...any calculations I should perform to model this? Thanks again

 

[Studiot]

do you think another option may be to use a backhoe to dig out the area of soil directly in front of the sheet pile in order to relieve some stress on the pile.

If, by 'in front' you mean lakeside.
Emphatically no it will make matters worse. This material is what is holding things up.

I still think there has been a failure at or below the toe of the piles.

I would dig a trial pit behind (shoreside) of the piles to see.

 

[srw2104]

i had actually meant landside...digging up in front of it may give me the room necessary to pull it back inward. do you agree?

 

[Studiot]

Since they are only 12 ft long you would be more likely to pull them out.
They are only baby piles.
Added to which you will get a pit filled with water which will attack the banks and cause further slumping.
It could be that the whole row is just too short and these are the first to start to go.

Why are you so reluctant to look for a source of the problem?

 

[srw2104]

when you say 12 feet long...you mean 12 feet deep, correct? ...and I am only looking for a temporary solution until I get the money needed for a permanant solution. I understand a permanant solution is best right away...but I jus cannot do that at the moment. I need a year and a half or so.

 

[Studiot]

I am against a significant amount of digging for the following reason.

Once you have dug a hole, any backfill you eventually fill it with plays no part in the subsequent soil support. Your founding level becomes the bottom of the hole and the backfill exerts what we call active pressure.

If you dig out semifluid (= failed) material this is no problem because it is alredy exerting active pressure.
But if you dig out competent material you are wasting resources and making the solution bigger, as competent material is at least partially self supporting.

 

[Studiot]

You said they were 12 foot piles.

I take that to mean that 12 foot lengths were driven in and now stick up say 3 feet, landside and 6 feet or so waterside.

 

[srw2104]

That is very useful information...I did not know. In addition, I apologize for the misunderstanding. When I say 12 feet...i mean they are 12 feet deep into the ground, with about 4 feet showing abover ground. So...giving a total 16 feet top to bottom.

 

[Studiot]

OK but even 16 feet is not really very long for permanent waterside piling.

I really think a small investgation into the very visible subsidence in your picture is called for.

I have to sign off now. Look forward to the enxt installment.

 

[srw2104]

Thanks studiot...youve been excellent help

Furthermore...Does anyone know of any formulas I could use that will apply to this situation which will allow me to further understand what is going on here. Any calculations at all would help...formulas for stress, load, strain, etc. Thank you in advance