Digging out - Drainage problems

[mattw]

Hi
I have removed a small (600mm) retaining garden wall and have been digging around a new conservatory with the intention of paving. Having dug to top of foundation the soil has turned to clay and a large amount of water is appearing everywhere. Is this normal? I am unsure if the water is coming up through the ground or from the garden where the wall was, although I actually removed the wall a couple of weeks ago and have had no problems until I started digging out. My builder says that the water is coming up through the clay and if I continue to keep moving it away the amount of water will eventually subside and it is not a major problem. With the amount of water that is there it appears to me that it is a problem and I am concerned that 1) is he correct and the amount of water will indeed subside? and 2) will the ground be suitable for paving afterwards i.e. will the water return? I intended to pave the area and use linear drainage but would you suggest that a land drain may be more suitable given the conditions? I also intend replacing the retaining wall with a flag retainer (any advice on weep holes?). Any help would be greatly appreciated.

[lutonlagerlout]

i would say the water is coming from where the retaining wall was,
the chances of water coming UP through clay are unlikely to say the least,PLUS it has rained a lot lately
if you get your drains in right should not be a problem
regards LLL

[mattw]

Thanks mate.

Would you say a linear drain would be ok or would you suggest a land drain would be better.

[Tony McC]

Clay is usually impermeable. It doesn't allow water to soak away through it, so that means it won't allow water to bubble up through it either. It's far more likely the water is coming in from the surrounding ground draining down into the sump you've created by all this excavation work.

Linear drains are intended to take away the surface water: land drains collect sub-surface water. There's a good chance that, once you get the paving installed, there'll be no need for sub-surface drainage, but without seeing the site, it's impossible to say. If you think the ground is particularly prone to waterlogging, then a perimeter land drain can't hurt.

However, at some point, you will have to consider what to do with the surface water on the eventual pavement that you're in the process of building, so a linear channel may be the answer.