Pouring footings in wet clay.

5 Jun 2011
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United Kingdom
Two weeks into a double garage build. Under 30m2 so no Building Control.

Perimeter footings 36" x 18", then an 8" reinforced raft.

We're on clay. Varies across the site from very hard even when wet, to slightly squishy when wet.
So far the trenches for the footings are down 2ft, another foot to go, but they have standing water in the bottom which isn't draining away.
Our builder was intending to start pouring the footings when we get to depth, 'the water will float to the top' said he.
Now, he's no incentive to bodge things as he's on dayworks, and I think he's a pretty conscientious chap but perhaps just not that experienced on wet ground.

Pouring on wet clay doesn't seem a great idea to me - shrinkage, settlement.

There seem to be various options such as compacting 4" of stone into the bottom, or treading concrete into the bottom and leaving it to set, or using something like Cordek EPS although that isn't intended for footings and anyway requires a good base.

We can pump out the standing water, but this will still leave the soggy bottom, and forecast is for more rain.

And, at the front corners there are 4ft deep pits for two RSJs, which of course are also full of water. If we were building a pond our clay would be perfect.

The raft can be left until later as we are building the dwarf walls off the footings, we could even leave the raft until the roof is on, but if we have to leave it to dry out to pour the footings we could be waiting for weeks.

What methods have you successfully used to build on wet ground?
Within reason, getting things moving is more important than cost.

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On the morning of the pour, pump out the trenches, scrape some of the muddy stuff off the bottom and get it in.

Having modest amount of water present will not effect the concrete.

Pouring on wet clay doesn't seem a great idea to me - shrinkage, settlement.
Irrespective of what the weather is doing presently, you have clay sub soil and all the problems attributed to it, whether that be excessively dry or excessively wet weather.
Down to 3ft now, and on one side where we were in made ground, down to 4ft. Bottom is drying out. Looks more hopeful.
Structural engineer came to look today, said so long as we bail out any standing water it will be OK.
Here's hoping for a few dry days, hurrr.

The day before the readymix & concrete pump were coming, I hired a puddlesucker and pumped out most of the water.
On the day, weather was dry, luckily. We bailed out the rest of the water and skimmed the gloop off the bottom.
Between 1400h & 1700h, 10cum of concrete went in the ground.
Next drought we have, I'll find out whether we should have waited a week or two.

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Next drought we have, I'll find out whether we should have waited a week or two.
Unfortunately you have clay subsoil.
Irrespective of whether you waited or not will make no difference on future weather influences.
Your clay will continue to shrink or swell according to water content.

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