Combined Footing for Confined Retaining Walls

• Oct 26, 2023

• #2

WesternJeb

Structural

Sep 14, 2023

270

To me, these forces just get internalized into a classic bending moment in the footing and tension force.

I can't envision how designing it as full wouldn't produce a design result greater/more conservative than what you have shown.

 

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• Oct 26, 2023

• Thread starter
• #3

StrEng007

Structural

Aug 22, 2014

507

Yes, to me it's also very conservative to apply Va and Ma to both sides of the footing at the same time.

Is there a way to lessen these into shared forces?

 

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• Oct 26, 2023

• #4

WesternJeb

Structural

Sep 14, 2023

270

The likelihood of that area getting filled to the brim, even if it isn't supposed to, in its lifetime has enough of a chance I would design for it. I would find it hard to justify in court why one wouldn't have designed for it to be full to the brim with that small of dimensions.

If it were say 50' wide, then I would agree with you. However, if they are close enough to sit on a combined footing, I think they are close enough that it could accidentally fill up.

 

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• Oct 26, 2023

• #5

Celt83

Structural

Sep 4, 2007

2,003

this is a condition where you would want to look at the base as a beam on elastic soil

 

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• Oct 26, 2023

• Thread starter
• #6

StrEng007

Structural

Aug 22, 2014

507

Western, I'm assuming it will be filled to the brim. I guess my question has more to do with what Ma and Va you'd apply to the top of the combined footing on each side. While this is an actual design I'm handling right now, it feels like a silly theoretical problem a group of engineers would debate on.

Celt, good idea.

 

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• Oct 26, 2023

• #7

Celt83

Structural

Sep 4, 2007

2,003

if your software has the capability model the whole 2D system with the base beam supported on compression only springs

 

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• Oct 26, 2023

• #8

KootK

Structural

Oct 16, 2001

18,105

this is a condition where you would want to look at the base as a beam on elastic soil

Click to expand...

To what end? Like WesternJeb, this feels like a pretty rudimentary statics thing to me. And not worth the effort of a more sophisticated, beam on elastic foundation design.

 

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• Oct 26, 2023

• #9

KootK

Structural

Oct 16, 2001

18,105

In the interest of design efficiency, I'd be inclined to just pretend that one wall isn't there and design everything like a classic retaining wall. If you want to avail yourself of the reduced soil pressure associated with the limited backfill extent, go nuts. Then just make the thing symmetrical.

 

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• Oct 26, 2023

• #10

Celt83

Structural

Sep 4, 2007

2,003

The question was how the foundation shares the load, if you follow the typical rigid foundation approach the moments would cancel and you’d get uniform bearing. If the foundation isn’t rigid then I’d think the moments would tend to lead to higher bearing out towards the toes. (The classic retaining wall approach for each side might be reasonable, I’d have to run the numbers the different ways to satisfy myself)

 

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• Oct 26, 2023

• #11

KootK

Structural

Oct 16, 2001

18,105

Celt83 said:

If the foundation isn’t rigid then I’d think the moments would tend to lead to higher bearing out towards the toes.

Click to expand...

Certainly. So much so that I suspect that most of the footing would be in a state of uplifting from the soil which, in my mind, would pretty much neuter the validity of beam on elastic unless it's a pretty sophisticated version of that. For the sake of looking at soil stresses and toe forces, I'd think this to be nearly as meaningful. If the dead load prevents footing separation of the soil interface, so much the better.

 

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