What do you do to ensure the integrity of a small concrete pour when your pad excavation bottom is a foot or two beneath the water table?
I’m thinking a small overdig, to enable the end of the inlet of a construction pump, then pump it, place form and stake it, pour, keep pump running for 45 to 60 minutes, and we’re all right after that.
What has been your experience?
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Replies
overdig a foot, drop a load of 57 stone to grade and pour concrete on top of that, real dry mix 4000 psi
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Haga su trabajo de fricken
Gene,
I had something similar to that. Dug a trench for footing, before I could get in the rebar and concrete it filled right up with water. I won't go into the painful details but my No. 1 problem was the sides of the trench collapsing on my work when the water soaked the walls. Kept having to dig it out. The only way to prevent that is to get a pump going immediately and keep it going the whole time. Use a pump big enough that a good rain doesn't overwhelm it. That's what was killing me. Trench was about 3/3.5 feet deep, bottom half into clay. yuk. The water make the clay into soft muck which I didn't like the idea of pouring concrete into. I had an engr out for advice he said what brownbagg suggested, rock at the bottom. My god, that s#%ked.
Good luck.
- r
When you say PAD, do you mean a small slab or an individual footer under a supporting column?
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Not a slab. A pier pad under a column.
In heavy industrial work, we did these routinely (albeit at a much larger scale) by pumping out and keeping pumps active while placing a stiff mix.
A four-foot diameter caisson with a belled bottom, even with ten feet of water in the bottom, is just poured. But the crete volume in work like that is such that the relative amount of water cannot really waste enough of the total mix by dilution to amount to anything. Get the mix in fast, and what water there is comes out on top.
In small scale work, however, what do you do?
Same thing. As long as the base is firm, I pour and let the water float off. But the kicker is knowing if the base is firm. More often that not is isn't so it becomes a judgement thing. The safer ride is to overdig, tamp in some stone and then pour, wet or ahead of pumps
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Why not set a precast pier?
I'm thinking a small overdig, to enable the end of the inlet of a construction pump, then pump it, place form and stake it, pour, keep pump running for 45 to 60 minutes, and we're all right after that.
Yes, exactly that. Overdig is slightly deeper than pier so pier bottom stays dry.
carpenter in transition
Edited 9/18/2007 6:44 pm ET by timkline
another thing we have done, when you have a pump truck. stick the hose in the mud and start pumping, once the concrete breaks the surface, pull out the hose..Haga su trabajo de fricken