Foundations for extension keep filling with Groundwater ####HELP

[SKMCR]

We have currently dug out the foundations for a double story house extension. The land is clay and the trench ready to be filled with a concrete pad for the brick build up.

However the trench keeps filling up with ground water. We believe its a natural water table as we have this under the void under our house too.

How /when do we get to fill this with concrete?Will the concrete set in time before it fills up again?

Is this something that builders face?what's the solution here.

Please help.

Concrete will set under water as it’s a chemical reaction. I’m sure you builders will a have it all sorted

I’d agree that if you’ve got nice sticky clay that isn’t collapsing in, I don’t think you’ve much problem just by having water in there.

Thanks it was just the amount that it was filling up. It fills up the trench in 7 or 8 hours which seems fast although we are the lowest of the properties on the row.

Thanks and welcome anymore advice from anyone.

Builders will need to pump the water out and scrap off the bottom layer of clay. Clay that is exposed to water will soften so you need to remove it before casting the concrete.

Likely, the day the pour is due, they will pump it out, scrape the mud off the bottom, and tamp down a layer of dry lean mix which will absorb some water and give a clean base.

It will be quicker and safer to have a concrete-pumping company squirt the mix in, rather than trying to barrow it or drive a truck over soft ground. examples

Do you think recent rain has made it worse?

sometimes they need to dig a trench uphill of the site to intercept the water, and pump that out.

Get the BCO to agree to what they do.

Thanks all. Yeah I don't think recent rainfall has helped. The extension builds into the lawn where the drainage used to be crap in the lawn until we sorted the drainage out.there may be some run off from that.

If the ground is clay it's unlikely to be filling up from seeping in through the soil - clay is not very permeable. It's more likely to be coming in from surface run off.

Yes concrete will set underwater, no problem if the water comes in after the mix is poured. You would need a special mix and special placing if you wanted to concrete a trench already full of water though, so pumping out and scraping off any wet clay would be the order of the day.

Good stuff. Already have the pump which has done its job so far. I'm more reassured. Thanks