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Old 12-07-2011, 12:08 AM   #1
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Need help with a foundation


Good Morning,
I'm doing an extension to my house .

The foundation is already dug , When we were digging the walkout the extra 4 feet from the frost line ,
The side walls caved in as the bobcat was taking out the remaining dirt he went too deep ... So now the dirt is not solid . It was mixed with the bobcat ...
To add more complications to the mix it has been raining for a couple of days
If i put a pump in the hole to removed the water It's still gonna be a lot of mud
Can i just frame and pour concrete on the mud If i remove the mud then my footing will be 2 feet at least thick ...
What is the best idea for me ?
It's just getting colder , i just want this done so what could i do?
Plz help !!!


Last edited by Mr J; 12-07-2011 at 12:17 AM. Reason: editing
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Old 12-07-2011, 04:55 AM   #2
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Ayuh,.... Replace the failing mud with compacted stone...

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Old 12-07-2011, 05:48 AM   #3
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It helps to know your location....but as you have already figured out....now is not a good time to do foundation.

When I was doing my foundation this summer for my addition...we went a little too deep....the architect said it was better to just use more concrete than put in uncompacted soil...

I'm going to assume the compacted stone is about your only option...

But I would wait until you have dry spell before pouring concrete....
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Old 12-07-2011, 07:32 AM   #4
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The base of the concrete foundation needs to be strong. This generally means undisturbed soil, or compacted structural fill. You state you have mud, which is clearly unacceptable as the base for a concrete foundation. Best is to wait until the soil dries out, if that is not possible, you can pump out the water, excavate the mud and other unacceptable soil, and backfill to appropriate elevation with crushed stone or structural fill. Either way, you need to compact the placed material.

Placing concrete on wet mud is likely to lead to long term, serious problems such as settlement of the foundation. By the way, placing concrete in cold weather, even freezing weather, is not particularly difficult, it simply requires a knowledgeable professional concrete contractor, and it will cost more than placing concrete under normal conditions. Placing concrete in a rain storm is trouble, I would never do it unless someone put a gun to my head, it is difficult to get the concrete to cure correctly, and finishing is a real pain.
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Old 12-07-2011, 03:15 PM   #5
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I live in Toronto Ontario Canada by the way ..
Would hammering pieces of rebar into the ground and putting rabar lying down with ties in the footing help it structurally from cracking due to the cold temperature?

How could i insulate the footing? would i have to?
So it doesn't fail with this cold temperature .
Its still in the very low positives here all week it's gonna be positive 5 - min 3
should i be ok with pouring?
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Old 12-07-2011, 04:17 PM   #6
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Hi! Saw your problem with the footings. Trying to understand whether your excavation is for a slab or strip footing, as it is not clear. This will make a huge difference. Here as some basic facts about concrete you need to consider
  • The base must be undisturbed compacted clay or load bearing material. Mud is no good and must be removed when dry.
  • Concrete devolpes heat in the curing process, so bulk concrete is ok to pour in the cold, but not too cold. Lowest recommended temperature is about 10Deg centigrade or 50Deg F.
  • Reinforcement in these conditions is essential. Run the idea past a structural Engineer.
  • If much moisture is present, lower the water content of the concrete, making for a stiffer mix so if extra water is absorbed, it will not weaken the concrete (the greater the water content, the weaker the concrete)
  • Remember some clays are very expansive, especially near the top of the trench and can vary 4'' in height from summer heat to winter wet. That's why trenches are dug to 18'' to 24'' or more to avoid this top layer.
Some photos of the excavated site would help enormously.

Cheers from Oz.
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Old 12-07-2011, 06:12 PM   #7
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Quote:
Originally Posted by Daniel Holzman View Post
The base of the concrete foundation needs to be strong. This generally means undisturbed soil, or compacted structural fill. You state you have mud, which is clearly unacceptable as the base for a concrete foundation. Best is to wait until the soil dries out, if that is not possible, you can pump out the water, excavate the mud and other unacceptable soil, and backfill to appropriate elevation with crushed stone or structural fill. Either way, you need to compact the placed material.

Placing concrete on wet mud is likely to lead to long term, serious problems such as settlement of the foundation. By the way, placing concrete in cold weather, even freezing weather, is not particularly difficult, it simply requires a knowledgeable professional concrete contractor, and it will cost more than placing concrete under normal conditions. Placing concrete in a rain storm is trouble, I would never do it unless someone put a gun to my head, it is difficult to get the concrete to cure correctly, and finishing is a real pain.
Outstanding post by Daniel, I couldn't agree more on all of his points.

We're currently in the middle of a fairly large (32'x70') garage/crawlspace addition, and our weather is struggling to make it above freezing this week. Fri. is supposed to be a high of 24 degrees, so we won't even bother as it's supposed to be warmer next week.

Main points: Get the disturbed soil out PERIOD. Either pour much thicker concrete, compact stone as Dan stated, look into "flowable fill/lean concrete" to make up the distance, or just lay an additional course or two of block (if it's a block wall). Nothing short of removing the soft soil will likely be adequate.

Also you need to cover the footings for at least a day or two so they don't freeze before gaining marginal strength. You also need to keep the frost from going below the footings and any post pads, for the rest of the winter. Baled hay or straw is extremely cheap here and does the job. Pain to clean-up, but I wouldn't advise purchasing insulating blankets for a one-time use.

You can also have additives put in the concrete to lower it's freezing point, as well as accelerate, but concrete generally doesn't cure very well under 40 degrees or so, so it's best to cover it after pouring to take advantage of the heat it's generating.
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Old 12-07-2011, 08:30 PM   #8
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I cant get a picture as of of now but these are the measurements...

The excavator went to deep on the footing and now due to the mud i will have to remove the mud ...

That now will leave me with a 2 foot more or less footing is that ok ?

My idea is to frame the footing now with cut strips of plywood instead of 1 x 8's due to the new height .

Would this be an issue ? I Want to get to where the clay is undisturbed and not muddy witch explains the extra depth ...

While the excavator was there digging the 4 x 8 and 4 feet depth , i guess due to the rain in the previous days the sides caved, now it rained again since and the 4x8 x 4 feet deep walk out is buried i have to dig it out again ...
what I'm worried about is now that i have to get rid of the mud will it be an issue having such a thick footing?
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Old 12-07-2011, 11:49 PM   #9
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Thick footings are not a problem, only an expense. It will likely be cheaper to compact gravel, as suggested above, but as far as I know, concrete can be 15' thick if you want. You should very likely have compacted gravel under your footings/slab anyway; a capillary break being one reason. I know you are against the cold wall, but do this right, or you will possibly regret it.
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Old 12-08-2011, 02:46 PM   #10
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I'm assuming from your description, the site slab surface horizontal dimensions are 4'0''x8'0''. What I'm puzzled by is you say it's excavated to 4'0'' deep? . Or do you mean by deep as in width by depth? Surely you haven't excavated a vertical depth of 4'0''. You wouldn't even do this for a small substation transformer.

If the slab is the base for an extension to the house, that is walls and roof will be built on it, you have to take the precautions raised in previous posts.

If the slab is simply an exterior walkout/deck and independent from the main house, you can be less particular.

Are you allowing a step down of one step, or is the slab meant to be at the same surface level as the rest of the house?

We are all trying to guess what is going on, so offering correct advice is next to impossible. However, guessing you need to make up 2'0'' of height, you can:

For instance, go with a waffle pad construction might be ideal for this site. This is where a polystyrene waffle form is used and a normal slab is poured on top. It has two advantages, you can remove 4'' of mud all over and as long as the sides of the mud are restrained and can't ooze out, you place 4'' of packing sand all over, compact and lay the polystyrene sub formwork. Then you reinforce the slab and pour high strength concrete.

This will give you a finished floor level of about 2'0'' above the sand.

This system also has the advantage of insulating the slab against frost, and uses minimal concrete. It is also one of the strongest slabs possible, and can easily "float" on the mud. It may settle a little (up to an 1''), but once it finds it's level, it won't move any more. Talk it over with your structural engineer. If the base is sound, it won't settle at all. Put a construction break between house and slab.

Photos please.

Cheers from Oz.
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Old 12-08-2011, 05:34 PM   #11
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Need help with a foundation


Quote:
If the slab is simply an exterior walkout/deck and independent from the main house, you can be less particular.
JoJo,... I read the Op as a Basement Foundation, with a walk-out...

Not a slab....

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