pad footing excavation under house keeps filling up with water..what can I do?

[Engineerataltitude]

I have a 87 inch square x 12 inch deep pad footing, at only 12" embedment, being retrofit under the framed floor in the middle of an existing house (to support a couple of new post loads at 29K and 15K...its a high snow load area) that fills up with water before the concrete can be poured. Soil was slightly damp when I originally inspected under the house, but clearly the water table is very shallow, so the councrete can't be poured as is.

Any ideas as to how to
1. either de-water this interior area effectively
OR
2. devise an alternate foundation support for these concentrated loads under the existing framed flooring?

 

[MiketheEngineer]

You could attempt to de-water by cutting a trench or pump. Unless you are really close to a lake or ocean - I find it hard to believe water table is this high - but it is possible. Did you hit a spring?? You can also use a proper concrete mix that will set under water.

But if the water table is that high - I wonder how good your soils are - esp with the loads you are calling out.

 

[Engineerataltitude]

Good point about the bearing allowable I used to size the footing. With all that water, it is suspect.

There is a seasonal creek that runs nearby that wasn't running when I did my initial site visit.

I think it may be time to have the owner call the geotech for this one.

 

[Ron]

If you place a load on the soil when saturated and then the soil desaturates (drains), you will likely get some small amount of settlement.

Good idea to get a local geotech involved. Might need to do some diversion.

If the water condition was static (there all the time), then you could excavate a post hole right outside your footing and pump from it. Don't pump from the footing excavation as you will disturb the bearing soils. Another way is to overexcavate the footing and backfill with gravel or a lean concrete mix. Let it set up, then place your footing concrete.