Under pinning of existing brick/stone walls 2

[n3jc]

Some old buildings have very wide stone or brick walls with no foundation or better said: the foundation = wall in the soil.
In many cases they are not deep enough.

I have some questions:

1. I usually see that only the half of the wall width is under pinned - is this OK? It doesnt look to stable in my opinion?! Wouldnt be better to do it under the whole width of the wall? Id like to hear some opinions/expriences (see attached file)
2. do you do under pinning from inner our outer side of the wall and WHY?
3. how to choose/calculate dowels for connecting old and new foundation?
4. is it possible to do under pinning on only one side of the building or not under every wall?

tnx for replies.

 

[PEinc]

1. I usually see that only the half of the wall width is under pinned - is this OK? I do not recommend underpinning half the width of a foundation. You need to check the required bearing area for the underpinning. If you underpin down to soil with the same bearing capacity, you need the same bearing area.
2. do you do under pinning from inner our outer side of the wall and WHY? Underpinning is usually done from outside the building. This makes it easier to remove the excavation spoils and deliver concrete.
3. how to choose/calculate dowels for connecting old and new foundation? Dowels are not usually needed. I would not underpin as shown in your attachment.
4. is it possible to do under pinning on only one side of the building or not under every wall? Underpinning is usually done only on the wall that abuts the excavation.

Check my web site for a presentation on the causes of recent building collapses in Philadelphia. The presentations describes typical underpinning.

http://www.PeirceEngineering.com

 

[PEinc]

More reading attached.

www.PeirceEngineering.com

 

[JedClampett]

PEinc, very good input. You guys (and gals) in NYC must have some big ones, if you know what I mean. I don't think I'd sleep (or go to the bathroom) until the underpinning was unnecessary and removed.

 

[oldestguy]

I've seen some very poorly constructed old walls, with one the exterior wall of a prison. I suspect the guys that built it figured on some day removing stones and escaping. You could shove a folding ruler all the way through that wall. What I am getting at is, it may take injecting grout in the old wall before any underpinning is done to "glue" together.

 

[PEinc]

OG, here's a photo of a rubble stone foundation wall with loose stones. Had to place some mortar before starting to underpin.
Jed, conventional concrete pier underpinning does not get removed.

www.PeirceEngineering.com

 

[Ingenuity]

Excellent SEAoNY presentation, PEinc. Thanks for posting this.

...and great photo too, PEinc.

Appropriate that a CHAINSAW is used by the 'carpenters' on an underpinning project.

 

[PEinc]

The SEAoNY presentation is very good but I do not agree with everything in it.

http://www.PeirceEngineering.com

 

[Ingenuity]

but I do not agree with everything in it

From a technical perspective, or the roles/duties of those involved, other?

Interested in your comments.

 

[bridgebuster]

Ditto

 

[PEinc]

Technical - w/r/t steel wedges and jacking.

http://www.PeirceEngineering.com

 

[bridgebuster]

thanks PEInc

 

[Ingenuity]

Technical - w/r/t steel wedges and jacking.

So you don't recommend steel wedges, but do recommend hydraulic jacking, or do/don't recommend either?

 

[PEinc]

I have designed and built many, many underpinning projects. Wedging and jacking are rarely needed - as long as the underpinning piers are DRYPACKED properly.

http://www.PeirceEngineering.com

 

[Ingenuity]

Thank you, PEinc.