Floating Garage Slab....What happens at the door

[bigmig]

We are the EOR for a house in an area with clay soils.
The soils engineer has identified the heave potential and has made appropriate recommendations in his report.
We have designed a floating slab in the garage.

The contractor asked a good question, that for some reason has never come up in my experience.
What happens at the man door (3 ft wide door)? The slab pours over the wall, so we don't have an unsightly slab-wall joint.
If the slab heaves....do they just plan on maintaining the door?

We certainly don't want to pin the wall down....do they just set the door with more of a gasket space?

Interested to hear others take on this.

 

[jayrod12]

We usually dowel at the doors. And to combat the heave potential at the doors, we also add some bottom steel to the slab and put in void form for roughly 24" away from the door. This acts as sort of a hinged slab that is intended on mititgating the heave at the door locations.

At overhead doors, we usually don't do anything special.

 

[XR250]

Sounds like you need a joint there. Should not look too bad as long as there is an 8" x 36" chunk of concrete over the CMU under the door.
Can you not dig thru the plastic soil and fill with stone?

 

[bigmig]

@jayrod12 the soils reports in clay soil jobs specifically says don't tie slabs to structure.
It will pick it right up. Imagine 600 psf uplift ability any surface area.

 

[Brad805]

You have two choices. Let it float, and the owner gets exceedingly annoyed when their door will not open. The second option is to have some dowels and live with some cracks if the slab does try to heave. If they want perfect, they need a pile supported slab or footings sufficiently deep to reduce the potential for heave. Home owners rarely want to pay for those options, but you need to have some notes to protect yourself.

What is the cause of the heave? High plastic clays or something else? If high plastic clays you need to pay attention to your perimeter drainage. The key with that type of soil is to try to keep it near its natural moisture content as much of the time as possible.

 

[DoubleStud]

I don't put dowels on mine. I do call out 4" of gravel and whatever recommended by the soil engineer. Typically they would say 2 ft of imported soil at the garage slab. What is more suspectable to heaving is the slab directly next to it on the exterior. Because right there you will have expansion material joint where water can easily go down into the subgrade. I don't typically call out imported fill on the driveway because soil report does not say so. I feel like between the garage being indoor, 2 ft + of imported fill, and the fact that it is protected by foundation walls that goes frost depth with perforated pipe, it gives me enough protection from the slab moving too much inside the garage.

 

[jayrod12]

@jayrod12 the soils reports in clay soil jobs specifically says don't tie slabs to structure.
It will pick it right up. Imagine 600 psf uplift ability any surface area.

We work on expansive clays pretty much exclusively here. I'm well aware of this. That's why we put voidform for the area adjacent the door, and only dowel at the door itself. The soil isn't able to push directly against the slab in proximity to the door, and if the slab further away heaves, the voidform and dowels allow the slab to hinge and the door operation isn't affected by the heaving. It has been used successfully too many times for us to change our ways.

 

[StrEng007]

What type of foundation do you have around the perimeter of your structure?

 

[canwesteng]

Don't pour the slab over the wall and live with a joint is the most common I've seen by far. Door opens out so it won't hit the slab. Not even sure how you can notice a joint, since the slab already has a bunch presumably, and in either case pouring over the slab creates some corners where you'll get cracking that is even more unsightly than the joint.