# Digging foundation



## healthyhomes (Mar 14, 2008)

Hey, hopefully some of the excavation gurus can shed some light on this.

We have dug out for a foundation about a month ago in good temperature. Now do to circumstances beyond my control, we cannot proceed with putting the foundation in until next spring. This means the hole will remain open through the winter. Where Im from (Manitoba, Canada) -30 degrees celsius is very commom throughout the winter. Can anyone comment on this. Is there anything to worry about? I am a GC, and we have never had to leave an open hole like this before!


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## Tinstaafl (Jan 6, 2008)

Well, the sides will cave in, you may wind up with a natural swimming pool that'll need to be pumped out, and unless you have the site well protected, animals and children may fall in and drown or starve to death.

Aside from that, I imagine you'll be just fine.


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## healthyhomes (Mar 14, 2008)

That was really helpful.... Are you an excavator, or a remodeller? Anyhow, This is out in the country, fencing is not a problem, I am aware of the pumping that will be needed. I am unsure about cave ins, and any impacts with changing the frost line, and soil conditions for the future footings


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## concretemasonry (Dec 1, 2006)

The cave-ins will depend on the soil type and the amount of moisture in it.

Since you have opened the hole and will leave it open until spring/summer, the frost will go into the soil just as much as the normal surface level. - It will thaw out at the same rate when it warms up. Pray for a lot of snow to insulate the ground and do not disturb or compact the snow, since that reduces the insulating effects.

Once the frost is out build to the usual requirements and backfill to prevent frost the next winter.

Basement in cold climates are not difficult, but you have to be quick (4 days from excavation to completing) and organized to meet the time schedule.


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## Tinstaafl (Jan 6, 2008)

I'm a remodeler who has dealt with excavations left sitting for too long, though I admit not over a whole winter.

I should have tossed in a smiley or two; I know it sucks to be stuck with that sort of a situation.

The sides _will_ cave in, guaranteed. Just how badly depends on the type of soil and overall weather conditions. The frost line won't change once all is said and done--once you build the foundation and backfill, your footer will still be at the proper depth and insulated by the soil above it.

With water laying in the trench (?) over an extended period of time, you most likely would need to deepen it when ready, just to get past the muddy layer created from all that moisture. It might pay to look into pouring your footer now and covering it for the winter with hay or some other sort of insulation to get around that.

Regardless though, I'd lose sleep over the liability potential of an open hole like that unless you have it very well secured. And even then, you never know what sort of idiots might decide to call it their playground.


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## griz (Nov 26, 2009)

How deep is the hole?


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## greg24k (May 19, 2007)

Don't worry about it...close it off so no one gets hurt and after the winter you put your footings and foundation. If sides cave in, you will have to clean it up...thats all :thumbsup:


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## skyhook (Mar 17, 2007)

_At least put a ladder in there.
:thumbup:_​


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## tgeb (Feb 9, 2006)

You've gotten some good advice already, and here is what I would do:

Partially backfill the excavation you have, toss in a couple feet or so of soil. It will protect the subgrade so you won't have to under cut in the spring to remove mud/frost.

I would also throw some soil around the perimeter so there would be no vertical sides that will "cave in"

Dig a trench so that the area will drain, if you keep it from becoming a pond there will be no need to bother with pumping.

It will cost a little, but in the long run I think you will be ahead in the fact that:
You will have a safe site, 
You will not be concerned about having to dig out a bunch of muck and replace it with concrete/stone.
If the circumstances change, you can dig out the frost in the early spring and get a jump on construction. 

Just my nickel...


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## concretemasonry (Dec 1, 2006)

Just make sure the frost is out of all the soil down to code or recommended frost depth it out. Driving a rod deeply will tell you reasonably well.

Nothing worse than building on a frozen soil that has layers that were not frozen before the excavation. You can easily have problems if the frost goes out after the footings and walls in in.


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## jdorpaudi (Nov 11, 2010)

tgeb said:


> You've gotten some good advice already, and here is what I would do:
> 
> Partially backfill the excavation you have, toss in a couple feet or so of soil. It will protect the subgrade so you won't have to under cut in the spring to remove mud/frost.


i am also in winnipeg, i would do what he says. as you know during spring thaw everything is a big mess, personally i would rather get rid of that top couple feet a muck, then redig it out to virgin ground for spring.
why does it have to wait till spring, we pour all winter...


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## S.R.E. (Apr 8, 2010)

tgeb said:


> You've gotten some good advice already, and here is what I would do:
> 
> Partially backfill the excavation you have, toss in a couple feet or so of soil. It will protect the subgrade so you won't have to under cut in the spring to remove mud/frost.
> 
> ...


This sounds like the best way to deal with your problem.:thumbsup:


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## DesignPlanBuild (Nov 6, 2010)

Cons: 
-your sides might cave in and plan on some clean up in the spring. 
- liability issues because of an open excavated site for a long duration of time. 

Pros:
Compaction. The soil at the bottom should be well compacted for footings and for your slab. Nothing compacts soil better than water. Better compaction = less chances of severe settling. 

Good luck !!


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## S.R.E. (Apr 8, 2010)

DesignPlanBuild said:


> Pros:
> Compaction. The soil at the bottom should be well compacted for footings and for your slab. Nothing compacts soil better than water. Better compaction = less chances of severe settling.
> 
> Good luck !!


I disagree.
It depends on the type of soil. A clay or silty soil will either need to be cleaned out in the spring (which will result in undercutting the sub grade which will require placement of structural fill which will probably need compaction testing by a soil engineer) or let to dry out till late summer before you can build on it.

Freeze and thaw cycles can and will loosen the soil.


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## jmacd (Jul 14, 2009)

Does the building have a foundation drain that leads out to daylight planned? I would dig that now so any water accumulating over winter can drain. 

You can also compact the area now or "cap" it so it will absorb less moisture over the winter. This works well with soils that will compact well like sand stone mix. The work area can still be considered virgin soil.


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## jmacd (Jul 14, 2009)

I posted before I read S.R.E but I would agree that if the soil is clay or silt you will have a mess until you get some dry weather. 

Depends on the code or inspector, in some cases you can't pour footings with any moisture in the trench and I have seen footings poured in water.


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## Vinny (Jul 21, 2007)

Tinstaafl said:


> you may wind up with a natural swimming pool


And at no extra charge:clap:


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## healthyhomes (Mar 14, 2008)

Thanks for all the great advice! We ended up being able to do it, just started now, which kind of sucks with the weather we are having!


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## tgeb (Feb 9, 2006)

So what are you saying, you are moving forward with the project and will not have to leave it open all Winter, or you're starting the dig and it will be open all Winter?


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## concretemasonry (Dec 1, 2006)

Brace the walls for support, since you cannot backfill with frozen soil.

Insulation batts on/along the footings.

Cap as soon as possible. This will allow temporary heat for work in the basement (electrical, heating/cooling and plumbing rough ins).

If you can get it framed within a few selected warmer days, you can set trusses and get some roof protection. Then you can work the interior with little weather effects.

Some extra heat cost, you will more availability of good sub trades and probably better prices.


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