Groundwater Level

cleveman

we've had a bit of moisture here lately.

I have formed up a slab-on-grade building and poured the footings, waiting for to pour the slab. There is an attached garage on this building and I put a mechanic's pit in there about 5' deep, maybe 4' wide by 16' long. It is concrete block with a concrete floor. It was a bit moist down there when I dug it, so I put in a sump pump pit.

Now for the question. The water level in the pit is 2 1/2 blocks (20") below the ground surface. In other words, if it were a bit longer and not full of dead animals, I could quite handily be swimming laps in it. What does this say about the surrounding area. Since this hole is at grade and the water is 20" below the ground surface, what hope should I hold for digging basements in this area? Obviously, this water can be pumped out, but what basement wall can withstand the hydraulic force of being submerged in water? I'm afraid it will either cave in or pop up like a poseidon missile.

rino1494

Is it only ground water and no rain water ?? With a proper footing drain system a little extra stone around the walls, I would have no problems with backfilling a foundation like this.

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cleveman

Some rainfall has contributed to the water level in the pit. And ultimately it is all caused by rainfall. But the rainfall is not being funneled into the pit. The area is slightly higher than the surrounding area, in fact. Other than a series of canals to help circulate the water, I'm afraid that a basement in this area would be like standing in a bucket. Unless you let the bucket fill up with water, it will eventually be crushed or pop up out of the water when you get out of it.

genecarp

do this if you are concerned http://en.wikipedia.org/wiki/French_drain

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funk5stacks

as long as there is some sort of drainage located around the pit/foundation you should be fine. you stated theres a sump pit, which should be adequate. the only time i've even heard of the situation you're describing is when i use to build custom gunite swimming pools, ground water was only a problem if their is no relief whatsoever. before a pool was poured the bottom drain would be extended with a stand pipe to ensure the possibility that the pool never "floated", immediately or during a pour. it has happened. you posted that you've installed a sump pit, which leads me to believe there's some sort of perimeter drain under the pit/foundation which is more than enough relief for the kind of pressure it would take to lift that pit and concrete slab off the ground.