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Old 10-31-2010, 09:40 PM   #1
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Lally column footing and high water table

I'm putting in a couple additional lally columns in my basement. I'm going to pour 2'x2'x12" footings for them to rest on, so I cut 2'x2' openings in the slab. My intention was to square out the hole and let the surrounding soil be the form.

My issue is that I'm running into a high water table and there is about 7 or 8 inches of water in the holes. I can pump them out, but they fill back up pretty quickly.

What are my options for pouring? Dewater as much as I can and pour?

Also, should I excavate further and add crushed stone underneath? Digging in the water has made it difficult to acheive a nice level surface.

Thanks for any ideas/advice.


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Old 10-31-2010, 10:03 PM   #2
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For purposes of this discussion, I am going to assume you have adeqaute basis for the size of the footings, the number of columns, and the location of the columns. So let's discuss concrete placement alternatives.

Option 1: You dewater the hole using a sump pump, or well point near the hole. This allows you to prepare the footing base properly, and place concrete normally. Of course, you need to keep the pump running during the preparation of the hole, although not necessarily during placement of the concrete (see option 2).

Option 2: You place the concrete underwater, using tremie technique. Since the hole will be full of water when you place the concrete, it will be difficult to properly prepare the hole, but there will be no problem placing the concrete if you get the proper mix.

Option 3: You place a waterproof form in the hole, and dewater by pumping out the form. The form could be a steel or other metal box, or even plastic. As long as you get a good seal on the bottom, pumping out the hole should be easy, and it should stay dry long enough to place the concrete. This will allow you to adequately prepare the base of the footing.

There are more exotic techniques for doing the job, such as preplaced aggregate, but they should not be necessary for such a small project. As noted, all of this assumes that the size and depth of the footing is adequate to support the column you intend to place.


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Old 10-31-2010, 10:52 PM   #3
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Thanks for such a quick reply. I appreciate it.

If I went with option 1, after I quit pumping, do I need to be concerned about the groundwater surrounding the footing and the concrete absorbing any of it? Or would it just simply increase the curing time?

Thanks again.
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Old 11-01-2010, 12:01 AM   #4
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The longer it takes to 'cure', the stronger the concrete is.
Slabs are often kept wet to improve them. Your pour should be in good shape.
Short of cutting off a body part, the worst that can happen in woodworking is manufacturing really nice looking kindling. --- Quoted from lenaitch
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