Structural foundation explanation

[rodwilsonsr]

This "foundation" has been sitting at grade. It's been like this for 20 years. I did not build this.
This is in northern Vermont, so the weather is fairly extreme.
There is about 3-4 inches of gravel under the concrete "footing", then anywhere from 2 feet to 6 inches of soil before hitting bedrock.
There is also a concrete wall right in the middle going the entire width of the house.
There is no concrete floor in the crawlspace, just this wall and footing around the perimeter of the house.

I discovered this lack of foundation because we started digging to put an addition on this side of the house.

We have taken the steps to pump concrete into this void since we are forming up walls for an addition. We went down to bedrock, drilled and pinned with rebar and filled right up to the existing concrete.

Can anyone suggest any reason why this structure has not heaved from freezing or sunk terribly from settling?
There is some settling in the house, but nothing that I would consider terrible. I would think it should be so much worse off.
The excavator guy is baffled the house is still standing.
Thanks
RW

 

[XR250]

Potentially, there was enough heat in your crawlspace to keep the surrounding soil above freezing.

 

[Once20036]

I had a couple initial thoughts:
1) If there's only 6" of soil down there, its possible that the ice is forming in this volume, but there's so little space that the volumetric expansion of the ice is insignificant
2) Its a sandy soil, such that there's room for ice crystals in between the grains without heaving.
3) There's enough heat escaping through the dirt floored crawl space that the ice isn't forming

 

[rodwilsonsr]

I should also mention, that for 15 of the 20 years, this place had no heat, water, septic, it was just used as a hunting cabin. I have improved it over the past 5 years to be a 3 bedroom house. So heat from the crawlspace preventing freezing was not a thing.

 

[lexpatrie]

Maybe it's "frost tolerant", or the ground freezes so quickly it doesn't heave. Or it's dry and it doesn't heave, or it's not frost heave susceptible soil.

Pretty clear it's never seen the "full" occupancy live load, considering the origin.

 

[XR250]

I should also mention, that for 15 of the 20 years, this place had no heat, water, septic, it was just used as a hunting cabin. I have improved it over the past 5 years to be a 3 bedroom house. So heat from the crawlspace preventing freezing was not a thing.

How do you know it never heaved during the un-heated era?

 

[canwesteng]

The kind of unstoppable frost heave that would lift a house off the ground is not a guaranteed occurrence and needs ice lenses in fine grained soils. So the reason it didn't heave is basically just luck. Think what would happen if frost heave was guaranteed to happen - no one could have a driveway that lasts over a year.