Is it possible to "foot" a floating slab building?

[jimgerken]

Can a building that was originally built with the floating slab, be later footed? I can imagine digging all around it and pouring a footing down 4-5 feet, then setting block up to nearly under the slab (thickened) edge, then shimming it to finish, etc, something like that. BUT I can't figure out how the excavated area can be back filled properly again. I can't excavate the exact volume that the footing and block need, I am sure that sand and dirt will tumble out from several feet under the slab edge, and it then becomes somewhat unsupported.
The goal is to minimize or eliminate the freezing cold Minnesota winter from getting under the slab and freezing the ground under the building wall, thus lifting it upward. If this condition is eliminated, I could then add my new house onto the existing garage properly. If the garage can't be footed somehow, the house will have to be built near but not attaching to the garage.
A few ideas have come up in our discussions. One is interesting me a bit. Imagine installing a 2 inch extruded foam board, outside the slab edge, vertically into the ground four feet (no footing in this scheme). The cold cannot penetrate thru the edge of the slab or thru the dirt under it for several feet down. The cold will not penetrate the dirt thru the floor inside the building anyway, because it will be closed up and heated to about 40 degrees air temp all winter.
Another idea we had was to build the footing and block wall, insluation board applied to the inside or outside of the bloock, then mud jack into the excavated unsupported space inside the wall thru core-drilled holes in the floor, a couple feet inside the wall.
Another idea was pumping the space full of isonene foam or similar.
A few other ideas got REALLY crazy.
Anyone with experience in this direction? What is commonly done? Thanks.

 

[Duffster]

I would excavate out about 4' wide and a foot or so deep and lay 2" foam horizontally and then vertically along the edge of the slab to the top then back fill.

As far as the footing if you poured a concrete wall you could pour up against the dirt bank. If you want to use block you could pump flowable fill behind the block wall.

 

[blueriver]

I would pour a concrete footing/wall from the desired depth all the way up to the concrete floor ... this would eliminate backfilling under the slab behind the footing wall.

It could be formed with 4x8 sheets to the top of your exsisiting slab ... stay out about 3 to 4 inches to run the concrete in the form and then after you pull the forms put your styrofoam insulation against the wall and back fill.

Clear as mud??

 

[Egon]

what is the purpose of the footer?

 

[Duffster]

what is the purpose of the footer?

Hold up the wall.

 

[wedge40]

I'm asking not telling.
Couldn't he dig the footer a few feet outside the slab perimetere, and then pour in the difference after the block is put up? Seem like he could splice some rebar into the slap to hold the new floor to the old floor.

Wedge

 

[ustmd]

Here in Texas and other areas of the Blackland Prarrie, we use a similar process to deal with post construction foundation issues due to the high level of soil movement we have. Instead of pouring a footer all around the edge of the slab, we either use a (50K ton) hydraulic jack to force (until point of refusal) solid concrete blocks into the soil under the grade beams at key points. On all of the blocks are in, the structure is shimed to level using steel shims. Alternatively, holes are dug and concrete piers are poured (my neighbor has piers going down 30ft) and then the structure is leveled. In either case, the entire structure is sitting on the concrete piers and is isolated from ground movement.

 

[gwjd]

why not build house and a breeze way with an exspansion joint like you might see in a comical building..... like a over pass to road joint then if the garage does move it does not really matter on the out side you could just use trim as the cover ......

also good fire break ....

 

[slowzuki]

Is the building heat? A footing or frost wall does nothing to stop heaving or slab movement if you don't have a heat source in the building.

Several states produce frost protected slab design guidelines, heres one, not the one I was looking for but its a start.

DESIGN GUIDE FOR FROST-PROTECTED SHALLOW FOUNDATIONS

 

[jimgerken]

Wow, already some good input! Thanks.

Yes, the building is heated, although to a fairly low temp, like 40 degrees F.

The expansion joint idea is kind of the default plan if nothing else seems workable. for the joint, I was thinking building the house with atttached breezeway pretty close to the garage, like a foot away, and around the doorway there would be an extension that could screw to the footed breezeway side, like a large extension jamb, and a layer of foam on the side where the garage door would be.

Glad I don't live in Texas, with soil conditions like that.

It still seems that the only method of filling under the slab, inside the thickened edge, is to pump it in there, pouring it will not make it flow uphill underneith.