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Bridge pier footing with sheet piling 8

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Panars

Panars

Geotechnical
Apr 18, 2005
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For the second time in my career, I have run across an existing bridge pier foundation that consists of a concrete footing with sheet piling around the perimeter. It looks like a normal pile supported pier footing, except there are no piles (like H-piles or pipe piles) under the footing, just the sheet piles around the perimeter. The sheet piles are driven in a rectangle and then the concrete footing is poured inside the sheet piles. The footing is a normal thickness (like 3 to 5 ft, 1 to 1.5 m) and is at the top of the sheet pile.

Does anyone have an idea how they designed these foundations? Are they designed as spread footings with an effective depth 2/3 the depth of the sheet piling (similar to a pile group)?
I don't think the sheet piling could be taking any significant load because the connection between the sheet piling and the concrete footing is relatively small. The connection is probably enough to provide lateral restraint to the top of the sheet piling, but that is it.


 
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I’m unsure of the connections but I am sure that I’ve seen examples of using SSP as part of the foundation. IIRC, Geotechnical capacity is derived similar to a steel pile. I’ll do a little digging around later and see if I can find any examples of the connections.
 
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If for sure no piles under the footing, perhaps they just left the sheets there to protect against erosion some day undermining the footing. I suppose no plans or other info.
 
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I don't have the loads, but I have attached the existing plans from 1953. One pier has the sheet piling. The other three piers are supported on HP14x73 piles. It appears Pier 1 was originally on H-piles as well, but then was changed to the sheet piling at the end of the design process. The bottom of footing is about 15 ft below the ground surface. PEInc, I thought of the idea that the sheet piling may have been there for support of excavation, but I didn't see how they would have removed the part above the footing. That would mean that the entire height of sheet piling would be abandoned.

I am aware of the recent research on using sheet piling for axial loads at bridge abutments. I was hoping someone here had some knowledge about how they would design something like this in the 1950's. I don't remember ever running across anything from that era that discussed axial loads on sheet piling. Which is what leads me to think they were designing the foundation as a spread footing. But I am just guessing.

Oldestguy, the soils at this site are mostly alluvial sand, silts and gravel, with quite a few cobbles thrown in for good measure. We have designed and constructed other bridges on the Great Miami River in Dayton using 16" diameter pipe piles with conical driving points with an ultimate capacity of 650 kips.

I mentioned that this was the second time I had run across something like this. The first time was the old Main Street Bridge in Columbus, Ohio, over the Scioto River. The difference there was the sheet piles were driven to shale (probably) and the connection at the top of the sheet piling had the SSP embedded into the concrete footing a little ways.
 
 https://files.engineering.com/getfile.aspx?folder=5747cd97-5d84-45a4-b5a3-f811d9055880&file=MOT-Patterson_Existing_piers1953.pdf
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Panars, you said, "I thought of the idea that the sheet piling may have been there for support of excavation, but I didn't see how they would have removed the part above the footing. That would mean that the entire height of sheet piling would be abandoned."

That's why I asked you about the depths from OG to top and bottom of foundation. It is not unusual for specs and plans to require that sheeting be left-in-place (L-I-P) so that voids are not created and the foundation undermined when removing the sheeting, especially SSP. It is also not unusual for the specs and plans to require cutting off L-I-P sheeting at the top of the foundation. In that situation, a problem can arise when the top of foundation is more than about 5' below grade. In that case, you would need more sheeting in order to safely cut off the original sheeting. And then, the new sheeting too would need to be cut off; and the the problem repeats to infinity. Some consulting engineers just don't know anything about sheeting, but that doesn't stop them from writing stupid specs.

 
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Also, the SSP shown on the old bridge plans looks like scour protection for the pier. Is the pier with the SSP in or against the creek or river whereas the pile supported pier is founded at a higher elevation, maybe on poorer soil and requiring piles, well away from the water where scour would not be a problem? The old plan shows the SSP anchored to the concrete foundation but that would not be sufficient to support the bridge load. It looks to me like the anchors laterally support the top of the SSP in order to resist lateral earth pressure and the lateral surcharge pressure from the foundations vertical bearing pressure when scour occurs.

 
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I lived in the Dayton area for several years; anything to do with bridges, dams, etc. was designed with consideration of the 1913 Great Dayton Flood. I'd bet the sheeting is for scow protection.

Everything I learned about SSP use was from a 1930's thru 1970's bridge contractor (my father). In the 1950's SSP for the described project would not have been intended for axial loading. As for construction, a 1950's, a bridge contractor would not have hesitated to construct a temporary SSP cofferdam outside and concentric with the permanently installed SSP.

[idea]
 
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Just got out of a meeting with the FHWA and they were also discussing the use of permanent sheet piles for scour protection. I'd think that likely too!

f-d

ípapß gordo ainÆt no madre flaca!
 
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That original plan detail for the "connection of the sheet pile to a footing" shows it was only for erosion protection. My view of that is there could be a failure of the pier support if significant erosion takes place outside of the sheet piles. They could easily deflect when that outside lateral support is gone. My "evaluation" of that is they have been lucky so far. Back about those days I met an engineer who came from Ohio DOT as a soil engineer to Wisconsin to get a PHD. From him it appeared the DOT then was ultra conservative. Not so here. Maybe due to the "waterproof wall" that sits between design and construction in many DOTs.
 
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Thanks everyone for confirming my suspicions that the SSP was just for scour protection. And to answer PEinc, all the pier footings are at approximately the same elevation. The footing with the SSP is on the "dry" side of the river bank. I put "dry" in quotes because it would still be under water at the elevation it was at, but the ground surface above it would generally be above water.

So if the SSP is only for erosion protection, would they just have designed the footing as a spread footing, ignoring the SSP for design purposes?

oldestguy, who was the engineer from Ohio DOT, if you remember their name? I ask because my boss is retired from ODOT and knew a lot of the bridge engineers.
 
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Panars said:
...would they just have designed the footing as a spread footing, ignoring the SSP for design purposes?
Click to expand...

SSP would not have been ignored for lateral confinement of soil under the footing.

Axial loading of the SSP would be ignored, for several reasons including the following:

1) The connection between the the SSP and the footing is poor for axial loading.

2) The sheet pile specified, SP-4 (later designated PSA 23), is "flat". It's low structural properties (moment of inertia & section modulus) make it a terrible choice for axial loading.

3) The SSP is "short" (25') compared to the expected length of the HP 14x73 used on the other piers. For any pier settlement under load, the SSP would have been expected to move with the pier. (Note: HP 14x73 tip elevations are not given. Instead the HP were driven to "required bearing of 60 tons per pile".) The piles are most likely "long", not point bearing, and pile tip elevation "is what it is" for each pile. For bridge work at that time the Modified Engineering News Record formula would have been used to determine pile bearing value... all of this is common practice for 1950's bridge construction.

[idea]
 
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