Thrust Resistance of footings of deep basement walls

[Berniedog]

I am designing a basement that is 14' deep. It will have 4000# of thrust at the base of the wall. I have the following questions:
1. Does anyone know how to quantify how much load a basement slab will take to resist this thrust?
2. I know I have read other threads about this but I cannot find them. Has anyone ever used helical pier tiebacks to resist this thrust?

Thanks for your input.

 

[msquared48]

Is this a full or partial basement?

Personally, at only 80 psi for a 4" slab, I wouldn't even worry about it. Just make sure the slab is in place and cured before the backfill is placed.

You also have the dead weight of the slab available to resist the force in sliding, plus the lateral bearing pressure of the wall footing against the soil to lower the 4000# per foot thrust. And there is the dead weight of the wall plus any vertical load it carries to further resist the lateral thrust through friction.

Shouldn't be a problem.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Berniedog]

Mike:

How can I quantify this?

 

[JAE]

In terms of concrete bearing pressure (4000 lbs/12" /4" = 80 psi) there's not a problem.

The only other limit state I can think of would be if there was some settling of the footings, or upward bowing of the interior slab such that the 4" slab-column would have a compressive force that would create PDelta effects, further trying to bow the slab upward.

So you could look at a 12" wide x 4" deep strip of slab as a horizontal column resisting the lateral force.

But the 4" slab weighs 50 psf which would counteract the upward bowing.

 

[csd72]

One interesting trick I have seen to ensure it is not a problem. Taper the bottom of the slab from thin at the ends to slightly deeper in the middle. That way the eccentricity has a tendency to push the slab downward.

We used to design vertical tilt up panels for some pretty substantial loads up to length/50 thickness and they would take loads much in excess of what you are applying.