Water filled foundation trench

[Geo57]

Hi all

I’m currently stuck with a fully dug foundation trench that I can’t fill with concrete as am awaiting a live gas pipe to be re-routed out of the trench

Despite being covered over, the trench keeps filling with water from surface run off

When it finally comes to being able to pour concrete, is it just a matter of bailing all the water out, or will I also neee to dig down deeper until I’m past all the damp clay from the standing water?

Thanks all
Geo

 

[23vc]

you can hire pumps for this which kick in when needed

 

[stevie888]

Damp won't matter at all. Scrape off any clay that has softened..

BC will doubtless have a view though.

 

[Geo57]

Thanks both - am down 1 metre deep already so scraping off the mud at the bottom seems preferable to having to go deeper!!

 

[johnny2007]

Dirty water pumps can be hired or purchased for a reasonable price.
The weight of the wet concrete will compact the little soft clay at the bottom of the trench.
When pouring the first bit, ask the concrete guy to make it less wet so any remaining water will be soaked by the first bit of concrete.
Happens to all building sites

 

[Ivor Windybottom]

I've been surprised before that concrete, despite being water based, doesn't really mix with water at all when it's poured. The water will float on top of the concrete and get pushed out as grey slop. But if you do this then you will end up with a weak flaky crust on top, where the top layer got diluted.

I've got a cheap dirty water pump but wouldn't recommend it. There's a tiny valve inside it, I think it's to let the air out so it can self-prime. One grain of sand in this will disable it, I've ended up stripping it all down a couple of times.

Your best bet is to hire a pump.

If you're going to jump in then get someone else there watching, just in case there's a collapse.

 

[stevie888]

We often pour concrete underwater. The thing to avoid is concrete falling through water or flowing water over the surface. We usually either drop the concrete through a "tremi" pipe or direct from a concrete pump and keep the end of the pipe under the concrete surface.

There is negligable mixing of water and concrete

 

[Wayners]

I hired a pump for the 4 days before inspection.
Sun came out and dried it mostly before concrete.
Not a problem but was stressful when it was hammering it down.
I got the wrong type of pump as well and couldn't get it to prime in the shallow water so had to swap it.

 

[^woody^]

There is a risk of collapse of the sides, depending on how well bound the soil is. You'll need to judge it.

You will also have to remove any softened ground at the bottom of the trench, down to a suitable hard level - otherwise you risk uneven settlement of the foundations later.