Garage Floor Slab

WNYcarpenter

I have a question I hope someone can answer.....

I just busted out the front 1/3rd of a 25 yo slab because it heaved and cracked. I'm in snow country so ice is a pretty big factor here. Ground water is a problem at this location so the cause of the failure isn't suprising.

We're adding drainage under the slab, a sump pump, and trench drain in the apron.

After the demo we found that the garage foundation block was "dry" layed beneath the opening and has also heaved and bowed. The soil in this area is undisturbed for 25 years and has settled around the existing foundation. Initially, I thought the best plan would be to excavate and re-lay the block with mortar, backfill then pour.

The more I thought about it... The soil is undisturbed, we don't footer drive-ways or patios, why not just backfill where needed, tamp, level with stone and pour without re-laying the block. I've gotten mixed answers so I thought I'd ask the same question here.

I'm confident we're solving the ice/water issue, so what about the slab settling?

Sorry for the long post!

neolitic

If you don't want it to heave,
you need to be solid all the way
to the footer, and a clean break
with the apron.

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Chris Johnson

Run the wall to the footing to avoid frost heave. You can pour it monolithic if you want.

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sawyerEd

Frost heaving is caused by 3 factors, poor drainage, frost penetration into the ground, and expansive soils. Your on the right track by fixing up your drainage problems with tile and granular fill but how confident are you that the slab will be dry at all times of the year? You should install install Type IV Polystyrene board around the perimeter, vertical and horizontal over the drainage layer. And if the garage is unheated under the slab as well. pay particular attention to the area where the door is. Frost penetration will be 2 or 3 times deeper where the snow is typically removed around the building.