Concrete and Water Table

[Jack1991]

Good Evening,

I’ve currently dug my footings out for my extension and my BCO asked that half be stepped down due to the ground, however the stepped side has now hit bed rock which means i cannot go any lower and means i’ve hit the water table so the lower side fills around 10-12 inch of water but doesn’t get higher unless it rains.

My question is how do i go about concreting into this?

I’ve pumped the water out but still leaves an inch or two laying on the bottom of the trench but starts building back up slowly due to water entering through the water table at various points.

Could i pump it out half hour prior to the concrete arriving and line the water table side with visqueen and concrete onto this, or can i just lay the concrete into the remaining bits of water?

Thanks in advance.

 

[Scarlet Pimpernel]

The bed rock, if the BCO is aware of it, it should be no problem.

You could dig a small sump pit at on end to pump all the water out.
If it's clay at the bottom, try not to walk on it too much, it'll turn the clay into a slurry which will hold the water even longer.
If this happens, scrape the slurry off the bottom.

I've sprinkled some dry cement over the trench bottom before now, after pumping out the water, to dry the bottom out.
I doubt if the BCO will be there when the concrete is poured.
As long as it's not too bad, it'll be OK to lay the concrete into a wet trench.

Also bear in mind, water in the trench might cause a collapse of the sides.

 

[Jack1991]

Yeah the sides have already collapsed so will need removing before laying the concrete.

Some of it has changed to slurry yeah it’s like 2 inch thick on top of the bed rock.

I will pump water out before hand and sprinkle some cement down where the water table enters to try slow it down a bit.

Thanks