Allowing ground to freeze below foundatins during construction

[Gopher13]

I have this exact phrase in both my general structural notes and specification (both in the concrete and earthwork sections), "Do not place concrete on frozen ground nor allow ground beneath foundations to freeze." It is also written in bold and underlined. The attached photo is 10 days or so after they poured. The strip footing on the near side of the photo was just covered with poly with not additional sheltering or heating. As a result, the ground around it and under it froze. What is my move? Maybe one option would be to measure the elevation of the footing with frozen ground in relation to the footing with the unfrozen to see if it has moved at all. Then have them thaw the ground below and around the frozen footing and have them take similar elevation measurements and compare the two?

 

[cvg]

Then have them thaw the ground below ... the frozen footing

how do you know it froze? it would take days, maybe weeks at below freezing temperatures to freeze the ground to a depth of 1 to 2 feet.
if it is frozen, than how do you propose to thaw it?
also, it seems that the un-cured concrete was not protected from freezing which might be a larger concern

 

[oldestguy]

One possible out might be having proof that the soil below footings is non-frost susceptible. That generally means the P-200 fraction cannot be above 5%. Taking precautions now and applying heat in an enclosed zone may thaw any frozen soil. Time to stop and proceed properly.

 

[kipfoot]

This is not a technical answer, but my response might be something like, "The contractor failed to protect the foundations and underlying soil from freezing, therefore the contractor must get a geotechnical engineer to tell me that what these footings are sitting on is sufficient."

It looks like they intended to enclose it, but ran out of plastic.

 

[Gopher13]

I am not too concerned about the concrete. The temperatures were between 30 and 40 degrees F for about 5 days after they poured. Just to make sure, I am going to have them conduct some rebound hammer tests. Also, the concrete looks ok. It is not crumbly and it does not appear spider-webby.

After 5 days of curing, the temperatures dropped with lows in the single digits and highs in the low 20's (degree F). I have been on-site and the ground around the footing has snow on it and it feels frozen. Also, the contractor has dug elsewhere on-site and they told me the upper 6 inches of ground is frozen.

They have ground thaw units where they run a fluid through hoses to thaw the ground. It works pretty well.

Soil below the footing is less than 20% passing No. 200. I am not a soils guy but I think that is only slightly frost susceptible.

I guess in this case, with ok soils and only 6 inches of frost in the ground, I am not too concerned, but I would like to know what to do in the future if circumstances are worse.

 

[gte447f]

How deep is the footing? Does it not bear below frost depth?

 

[Gopher13]

Bottom of footing is 5'-8" below finished grade elevation. They poured the footings 2.5 weeks ago and are currently laying the foundation wall (masonry). Thus earth is excavated around footings.

 

[oldestguy]

From your 20% P-200 size that places this about mid way in the US Corps of Engineers classes F-0 to F4 of frost susceptibility. Not the worst but definitely not good. Time to lay down the law. Once things go bad it is not just the contractor, but also the engineer that must face the music.0

Edit: It is not the freezing that is the problem. Any water that contacts that frozen stuff, from below, sides, or above will then feed frost lenses that grow. It is this feeding of frost lenses that is the problem. Prevent any water, whether free or capillary from below will do its thing. The pressures created will lift any foundation not carrying monstrous pressures. When the frost lenses melt maybe things stay up, but usually at least some settlement occurs.