Foundation underpinning with overpour - concrete not flowing far enough under the footing

[Anton Polyakov]

Good day experts

I am doing a foundation underpinning at my house with overpour method. The issue I am facing is that overpoured concrete only goes half way under the 16 inches wide footing leaving a 1.5-2 inch gap at the rear part between new slab and the footing.

I use proper vibrator and vibrated hell out of it. Concrete was pretty fluid. One suspicion I am thinking of is - maybe the pouring gap was not big enough and it didn't create enough hydro pressure for concrete to go all the way under the slab? It had like 2 inch opening between the bottom of the footing and vertical form where the inclined lip was (you can see on the photo).

Any other hints what I might be doing wrong? It's hard to find any guides/videos showing the process itself.



Thank you for your help!

 

[miningman]

superplastizer is your friend under these conditions

 

[Anton Polyakov]

Any good suggestions for superplastizer? I've been trying this one

https://fritzpak.com/products/water...zers/supercizer-7-superplasticizer-admixture/

however honestly didn't notice too much difference in terms of fluidity in the field

Do I need to force pack the concrete under the footing with 2x4 or smth? I assume there's still a limit of how fat it can flow on its own
Does this depend on the hole size at all?

 

[EireChch]

From what I have learned from PEinc over the time on this forum, dry pack is your friend.

(Disclaimer - I will await PEinc's comments/confirmation )

All joking aside, you could pour concrete up to 4 inches below the footing base then dry pack the last 4 inches.

 

[Anton Polyakov]

hey EireChch, so the overpour simply doesn't work or am I doing it wrong? I thought it's the latter hence trying to figure out what I am doing wrong

Some people say it might be the air trapped

 

[jayrod12]

It does need somewhere to vent the air. So that certainly is possible.

 

[PEinc]

As EireChch said, drypack is your friend. Don't count on overpouring to provide full bearing under the existing footing. Pour the underpinning concrete to within 2.5 to 3 inches below the lowest bottom of the existing footing within the pier width being excavated. Then, install the drypack as a stiff, damp mixture of 2 parts sand to 1 part Portland cement. Ram the drypack hard into the gap a little at a time until the entire space between the footing and the underpinning pier is filled. Non-shrink and non-metallic drypack are not usually needed. Drypack the gap the day after the pier concrete has been poured.

http://www.PeirceEngineering.com