Underpinning

Nac

I have done some underpinning we usally dig 4' and skip 4' we use pnematic clay diggers a easier that pick and shovel to brake up the material. then pour footing and them 1 sided forms poured to the top and if neccsarry we use ns grout on top to pack in the voids.

LNG24

Guess whats underway? Yep, I finally started the underpinning. After a year of on and off discussions with an engineer, surviving a winter with hay bales protecting the exposed footing and constantly pumping water out, I jumped in and did it based mostly on what you guys told me anyway.

What we ended up doing was to dig back (by hand ) approximately 1/2 the width of the footing (to the inside of the wall its supporting) so that left a portion of the footing on existing soil. See drawing.

Here are the pics. Will keep you posted.

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rbsremodeling

Did you grout between the foundation wall and the new footing?

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LNG24

Nope: Engineer did not feel its necessary in this case since we poured about the bottom of the footing and not just to the bottom of it.

rbsremodeling

understood

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Redneckpete

What is going to stop the frost from penetrating THROUGH the base of the foundation wall and old footing, and freezing the clay that is still under the back side of the footing? The frost can still grab the soil and heave the footing.

That's why I always excavate the entire width of the footing, and usually form against the dirt at the back with a couple inches of SM.

Pete

Nac

Here is a job that still on going 1 building has been underpinned the other is in the works.

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Nac

Here are a few more.

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neolitic

Where are you getting this?
If the bottom of the footing is
below frost, that's the end of
the story.

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(Sorry....it seems there really are dumb questions)

LNG24

The bottom of the footing is now down 42". Frost would have to penetrate over 18" of solid concrete to even get to the back of the footing. A 4" slab is all that stands between heated space and the earth below. If we have a freeze that deep here, Hell is Freezing Over and I have bigger problems.

Typically, underpinning is done to carry extra weight of lets say additional stories added to the top of the building. Or you might have to do it if you are excavating a building next door deeper than the existing building.

In my case, none of this was present, we simply needed a Frost Wall, in fact the engineer said just building a concrete wall out of cinder block directly in front of the footing would be sufficient. I liked this version better.

I created this problem by calling it underpinning to begin with. It would be no different than building a frost wall around a poured slab.

ruskent

So lets say I buy alot in a city and want to build a building with a big basement. The building next door 5 feet away just has a crawl space. If the other owner doesn't want me to underpin his building and I out of luck?


I am just curious how the works. I am not really buying anything.

Nac

If the building is 5' away and you will still undermine it in building your new basement and they do not want you to underpin. Then you would install soilder piles and lagging on the property line. If you can not install tiebacks into there property then usally you install steel H piles with a 1-1.5 toe as long as the soil can hold it.

LNG24

My walk out is finally done. Well, except for putting the bluestone on the steps and top of wall.

Here ya go:

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LNG24

and done...

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woodmagman

I too am confused, this is a walk out. The footing is only 18 inches deep. If you do not get frost there then I see no problem, but in a lot of places across the country frost goes to 4 feet… and that footing is not protected. If it was put in a heaving condition there are no piers or piles to keep it from moving.

tgeb

Looks good from here, It will look much better with the stone caps and treads.
Really helps out the basement area.

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Tom

www.gebcon.com

LNG24

Where did I confuse you? Footing/Frost Wall is now down 42" not 18"

Blockade

I am looking at this and see that the footing is only 18" below grade. When you remove soil and expose any area of the existing footing to the elements then that exposed area becomes grade and the level in which frost can penetrate. The only way frost is not going to be entering the equation is if you put a cover on the stairwell and heat the space. Or am I missing something?
Bill

rbsremodeling

Ok here is a simple, layman answer the new underpinning makes up for the dirt removed

So if you remove 2' of dirt the underpinning is 2' further down under the dirt.

So the footing is not exposed it is now back to the same depth as it was be cause of the underpinning.

Not really 100% accurate just making it laymen like

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rbsremodeling

You can get waivers in most areas if the neighbors don't comply. Having them sign off just makes the process easier and faster to get the city approvals

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