Underpinning wall hinge 1

[jandlo]

This is sort of a general question about underpinning. I see companies advertising underpinning like the detail shown below. How do they connect the underpin to the existing foundation to resist the moment? In general I'm curious how engineers detail similar scenarios so the new wall retains the soil.

 

[PEinc]

Usually, no connection is made. Check to see if the existing foundation wall is stable above the underpinning. Check if the foundation wall slide off or overturn from on top of the underpinning. Then check if the underpinning piers will slide or overturn with the dead load of the above building. Ignore live load in sliding and overturning calculations because live load will provide resistance to sliding and overturning. Consider live load when checking bearing under the underpinning piers.

If the existing foundation is concrete, it is possible to drill and grout in some dowels to connect the foundation wall and the underpinning.

Also consider the total height of the retained soil behind the existing foundation wall and the underpinning. Experience shows that if the retained height is about 10 feet or more, some lateral bracing will be needed. It may be more or less than 10 feet depending on the weight of the building and the size of the underpinning piers. Even if you can dowel the foundation wall to the underpinning, you still need to check the need for temporary and/or permanent lateral support.

http://www.PeirceEngineering.com

 

[DaveAtkins]

I agree with you, that is a hinge.

I generally show dowels drilled into the underside of the footing.

DaveAtkins

 

[jandlo]

Thanks for the suggestions. I suspected doweling into the existing footing would be required in some cases. I wonder how often it's done without dowels.

 

[PEinc]

I have designed and built many, many underpinning jobs of all sizes and depths. Newer use dowels because there are problems with rebar development length, grouting, and dry packing (which you do not show).
It would have been nice if your sketch had some elevations for the OG, new slab and bottom of existing wall footing.

http://www.PeirceEngineering.com

 

[jandlo]

This isn't my detail. It's from a website of a company who specializes in adding basements to homes.

How do you handle the hinge in the wall when underpinning if you don't use dowels?

 

[PEinc]

Please reread my first response.

http://www.PeirceEngineering.com