new building next to existing

[greznik91]

Hello,

I have been wondering what is the better option for the new foundation when building a new structure right next to existing.
New building will couse additional horizontal pressures on the existing basement walls.
How to minimize impact of new building on existing - to make the foundation slab or strip footings?
Contact pressures under the new foudnations are smaller under foundation slab, but is that all there is to it?

Thank you for replies.

 

[GeorgeTheCivilEngineer]

If at all possible I'd be matching foundation depth and reducing depth as you move away from the the existing building.

Surcharge loading wise, the raft should have slightly less surcharge as some of the wall load will be spread back into the raft. The worst case would be a strip footing and a suspended floor.

 

[XR250]

Maybe consider Helical Piers. Besides the lateral pressure, you are most likely bearing on backfill.

 

[HTURKAK]

I would excavate the previous disturbed soil near the existing wall up to ftg level and fill with blinding conc. then consider continuous ftgs vertical to the existing bldg..

My opinion...

 

[le99]

I think XR250's approach is the most promising, as it eliminates the additional lateral pressure due to the gravity load of the 2nd building. However, ties should be provided between the two buildings at the grade level to transfer the lateral load.

 

[dik]

Watch for the surcharge on the neighbouring foundation wall from your footing pressure. That's the reason to found at the existing footing depth.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JLNJ]

Does the existing building have the same Owner as the new building?

If I owned the existing building, I wouldn't want your new building affecting my existing building in any way - including additional horizontal pressure from your footing.

 

[XR250]

I would excavate the previous disturbed soil near the existing wall up to ftg level and fill with blinding conc. then consider continuous ftgs vertical to the existing bldg..

I would be worried that the concrete might blow out the basement wall (at least until it hardens) as the lateral pressure likely exceeds the existing backfill pressure.

 

[TigerGuy]

You would likely need to place that concrete in limited depths over several days. The basement wall was not likely designed for an equivalent fluid pressure of 150 psf. I like the helical approach.

 

[BAretired]

Neither the mat foundation nor the strip footing is suitable in this situation. You must protect the neighbor's property by carrying your foundation down to the same depth as his.

Do not rely on the neighbor's foundation to provide lateral support to your structure, because it may not always be there.

BA

 

[driftLimiter]

I agree with most here, you have to protect the adjacent property for the final condition and the temporary condition (@TigerGuy). Also I important to consider the adjacent load for both your soil bearing, and the soil bearing of the adjacent structure. The soil right underneath the interface is essentially supporting both footings.

 

[kipfoot]

something like this, in my opinion:

 

[HTURKAK]

You are right for your concern but i am sure one can simply calculate the max. pouring rate to avoid blow out of the basement wall.. ACI 347 suggests the following formula for lateral pressure of concrete ( p= 100+ 6000R/T ).. Depending on my past experience, (if the basement ht is 10 ft, the conc. fill ht would be 6 ft ) pouring the first 3 ft then waiting 2 hrs then pouring the remaining ht. would be OK..

I would suggest to look ACI SP 4 for more details and the following doc.