Water table level

[RogerS]

I've had excavated a 4m x 3m area in the garden down to clay subsoil. The concrete raft (reinforced) and about 6" thick sits on top of some rubble...built to Building Reg spec.

When I removed the shuttering and pegs, the holws soon filled up with water and the level stopped about 4" below the bottom of the concrete slab.

So will my slab stop the wtare draining away or, because the water table level is 4" below the slab bottom, then I can assume that water will still drain away? Or will 6 tons of concrete compress the soil and stop drainage?

I am thinking that I might dig a deeper trench around the slab and stick a land drain in to help take the water away to help drainage in the garden. But if I do THAT do I then change the dynamics of the slab and run the risk of subsidence or the slab tilting?

Any thoughts very welcome.

 

[trevtheturner]

Hi Roger,

I would be surprised if your concrete, properly laid on top of hardcore, would have any adverse effect on the subsoil. As I recall, your land is fairly 'high up' so, even with a clay soil, I would expect any surface, or just under, water to find its own drainage channels in due course, even from a disturbed area.

Was the water in evidence at all before the excavated area was filled in, indicating that water is draining from higher ground and being held at your place? I would have expected any water to continue draining to the ground below you.

You could try digging a couple of holes a few yards either side of the site to see if they fill to the same level, indicating that the area generally is holding some water (at this time of year?). I have about an acre of land at the rear of the house which slopes gentle upwards towards its top end. The soil is fairly heavy clay so holds water and remains pretty wet after the winter until late spring/early summer, even with many trees taking a lot of moisture from the ground. However, this has never caused a problem to our buildings. We know that the natural water table, with drainage down from the hills behind us, is 40 feet below the house - I know this 'cos that's the depth into the well from which we pump our water! I would expect that your natural water table is at the bottom of your 'driveway' :wink: .

I wouldn't expect your new concrete to be going anywhere (I am assuming that the ground was, previously, largely undisturbed) and, for the time being, I would just keep an eye on it and give the disturbed area a while to settle before deciding on any additional drainage. FWIW.

Are you building a new 'rat 'shop, then? :shock:

Cheers,

Trev.

 

[tx2man]

One acre of land eh.... Squire Trev?

TX
dothing cap, tugging his forelocks :shock:

 

[trevtheturner]

Nah, I'm not a Squire, TX, just an ordinary bloke :wink: . Just moved out of the south-east ten years ago, the land came cheap with a big, old house - and I've been 'doing it up' ever since :? Not finished yet :roll: But we wouldn't change it for anything

Oh, and BTW, it wasn't a gloat - not my style as it 'appens. Just trying to help Roger with my own experience of water in the ground.

Forelock tug returned with compliments :wink: .

Cheers,

TYrev.

 

[tim]

Nah, I'm not a Squire, TX, just an ordinary bloke

Thats not what your gamekeeper says. :lol:

T

 

[DaveL]

Thats not what your gamekeeper says. :lol:

Well everyone needs someone to put the Monopoly away neat and tidy. :roll:

 

[trevtheturner]

Aw, c'mon, Tim. Okay, okay, give my secrets away then.
:lol: :lol: :lol:

DaveL - :lol: :lol: :lol:

BTW - sorry, Roger. Anybody else got any suggestions to help Roger with his water?

Cheers,

Trev.

 

[RogerS]

Thanks, Trev, for the suggestions. I'd sort of come round to the same way of thinking but it's good to get a second opinion.

Monopoly?

 

[Anonymous]

Hi Roger,
My experience of a clay garden with a high water table would recommend leaving it and seeing if anything untoward happens before jumping in with additional drainage. My experience of adding new foundations for a base (in my case crusher run - might be called something different in your area) actually aids drainage - the water drains through it easier than the clay. Some of my neighbours have gone the whole hog and laid pipes and stuff. This, in my opinion anyway, has ruined their gardens - draining away what is, in effect, the main advantage of clay soil - water and nutrients! The plants grow better and my lawn is still green in the summer. If you find there is a problem, try the easy stuff first. My garden, when acquired, had not been changed for about 50 years, so the the soil was very compacted anyway as it had not been worked. Adding soil conditioner works wonders for drainage in clay soil. Whenever you do any digging, put some in. Plant moisture loving plants (have you seen a 6ft Gunnera - spectacular - Try growing that in dry soil!). If you have grass and spike it, use the hollow tine aerators (the ones that remove a plug) rather than using a fork, as you are compacting the sides of the holes.
Regards,
Col.