Very high water table

[chuckey]

I am just starting blocking up a 42" wide doorway (to turn it into a window) in a rock and rubble pig sty. Having lifted the flag in the doorway, and dug out about 9" of moderately hard soil, I have reached a layer of large stones, when I lift these, their holes fill with water. The water level is about 12" below the finished floor level. The bottom of the water is about the same level as the transition between the top soil and the clay subsoil.
Next summer I was intending to build a land drain around the building, but now is not the time to excavate deep holes in a field! The attraction of doing the rebuilding job is that the inner skin can be built in the dry.
The options I can see are:-
#1 build a sump to collect the water, hence dry the trench out.
#2 Leave the big stones (not really that big, say, grapefruit size), and fill gaps with pea shingle, rammed down, then build wall on top of this.
#3 Try to level bottom of trench and hammer in bricks on end into mud/clay so as to bring the bottom mortar course above the water level.
#4 Put the flag back and wait until next August.
Any other ideas?
Frank

 

[Andrew Bodenham]

I'd be guided by the depth of the foundations in the rest of the building. Presumably you can see how far the walls on either side of the doorway go down?

If you find that you need to go deeper then you'll have to try digging a sump adjacent to your trench and pumping the water out of that. This should have the effect of locally lowering the groundwater level, though complex factors like the porosity of the soils come into play here.

I'd be cautious about excavating too deeply adjacent to existing walls, especially if the ground is saturated, as you may induce movemet in the structure.

 

[Penners]

Are you an enthusiastic swimmer? Only I've got an idea.... :wink:

 

[Lime]

Attempting to drain the hole so near to your house foundations is not the way to go.
It is a modern method, so that work can take place in any conditions, and may result in ground movement.
Unless you are sure of your ground (sorry ) I wouldn't do it.
The watertable is a natural phenomenon and, unless other things have been done to make it rise, is best lived with.

 

[Penners]

Unless you are sure of your ground (sorry ) I wouldn't do it.
The watertable is a natural phenomenon and, unless other things have been done to make it rise, is best lived with.

I agree with Lime. Suddenly changing the characteristics of your groundwater can have unpredictable effects on the building.

 

[Cloudscape]

I would have thought that the water table is likely to be high at the moment, after two very wet years? (Don't know what the weather's been like in Wensleydale). I was discussing this with my neighbours, wondering if we currently have 'heave' (swelling of the clay) - and whether we'll all sink a bit, if we have a drier year or two.

 

[Andrew Bodenham]

Attempting to drain the hole so near to your house foundations is not the way to go.
It is a modern method, so that work can take place in any conditions, and may result in ground movement.
Unless you are sure of your ground (sorry ) I wouldn't do it.
The watertable is a natural phenomenon and, unless other things have been done to make it rise, is best lived with.

Valid point, though the dewatering method I suggested is a temporary solution. I doubt that any any serious movement would occur in the day or two needed to excavate and put in a footing for a short length of wall. Once the wall's up above ground level pumping can stop and the watertable can resume its previous level.

It goes without saying that anyone undertaking structural work should consider carefully if their experience and understanding is sufficient for the job in hand, and seek specialist advice if necessary.

 

[Penners]

It goes without saying that anyone undertaking structural work should consider carefully if their experience and understanding is sufficient for the job in hand, and seek specialist advice if necessary.

Unfortunately, in this litigious age, it doesn't go without saying. Hence the necessity for you to add that well constructed disclaimer.

 

[chuckey]

During Tuesday and Wednesday I used my wet and dry vacuum cleaner to remove about 25 Gallons of water. Interestingly at first, water ran into the pudding bowl sized depression at a very high rate, 1/2" gall/min?, a little squirt, looked very nice. At close of play on Wendesday, water level had reduced by about 1/2" in the pudding bowl. This morning just a muddy residue in bottom, so water table now > 18" below floor level. Points I have learnt, somewhere there is some sort of sump (remaining foundations?) of at least 25 gallons capacity. I guess this has been filled by the terrible amount of rain we have had over the last three weeks. The ground basically drains well. So tommorrow I'll get out there and try and clean the mud off the existing foundation stones and do a pour (of concrete - sorry!).
Frank

 

[Lime]

somewhere there is some sort of sump

It's called the local water table.

Nothing wrong with what you have done as a very short term measure but concrete!?!
God help us.