Water Table Issues - HELP !!

[maarass]

My basement was dug yesturday. The foundation will be formed out so this is the bottom of footing depth. Lot is sloped about 5-6 feet between
house stakes. The excavator went down and noticed some water. He
needed to go down another 10-20 inches for the 9' walls. Today he
notice more water comming up. Probabluy water table may be high because of all the rain. Alot of rain for about a week !! . Right now it's about 4 - 6" above bottom of footing depth in the low spots. If
it goes no higher will this be ok ? Foundation is 10" thick and drain
tile might be above this area. Oh, this is only at the one side of the
basement where it's deepest. The other side is a walkout. Can the
water table be lowered ? Excavator recommends throwing down about 10" for 3/4 clean over the entire pit. This would raise the house up some. G.C. is having a geotech chech it out. Can the footings be place on top of this stone? Will it give a stable base like undisturbed earth ? Does it need to be compacted ? Oh, the soil is very clayey, what about frost heave ? Sorry for all the questions, but I want to do this right. thanks

[Rich]

If you have high content of clay I would not put in a footing and instead use caissons, void form, and gradebeams. With clay there is typically an expansion factor associated with it. In some areas I've seen it recorded up to 18" of expansion.. trust me you don't want that anywhere near your foundation. I would first request the geotech does some soil samples to see just how much expansiveness the soil has. He may even have to drill some test holes.

[maarass]

Thanks for the reply. Well see what the geotech says. This sounds scarry and expensive !! I've heard that it's possible to build right on the water table if proper water management solutions are used. I personally see this as taking a chance and not a fix. Too many unknowns as of now. thanks

[RobBase]

Do what the excavator says......put down 10" of 3/4" crushed stone, not washed gravel. Crushed stone will be more structurally stable and it does not need to be compacted. Raise the elevation of the house up above the water table and raise the finish backfill grade around the house and you'll never notice.

The crushed stone is capable of supporting the footing and house loads easily. We use it all the time for the Corps of Engineers and they're real mother f'ers when it comes to specs. Make sure the drain pipe is put around the inside and outside of the footings at the BOTTOM of footing elevation and drains to daylight.

You don't need to worry about frost heave since your basement will be backfilled. At the walkout basement wall, you'll have to step the footings down so they rest on soil that is below the frost line. If you hit water there, again overdig below the bottom of footing elevation and put in 10-12" of crushed stone and pour the footing on top of it.

[maarass]

Thanks for the reply. We will be using interior drains as well. Out of curiousity why is 3/4" crushed stone better the the clean stuff ? Is it because it's has all those angles that make it fit together and not need to be compacted ? Geotech is going to get back to me. Anyone know about how much they charge for their evaluation ? Probably don't need one but it might pay off if county questions or methods. Thanks

[Rich]

A full geotech report is about $1000.. which includes some borings to check soil, a few more bores for soil percolation rates. The report will then give recommendations on foundation design - i.e. footing sizes for soil bearing capacities, caisson size and depth. They will also give the soil/rock encountered the full depth of each bore..etc..etc.
For a simple soil sample, which is all you should need, will run about 150.

[maarass]

Thanks for the reply. I will ask about a soils sample evaluation.

[RobBase]

Crushed stone locks together better due to the "angles" as you said. Washed gravel is sort of like walking in a box of marbles.

[maarass]

thanks for the reply, that's what I kind of thought. The geotech called back and said he won't do it. They are commercial and a report would cost 3-10K !! WOW !! Another basment contractor that been doing basements in my area for 20+ years says when they hit ground water the lay down some geofabric and throw down some crushed stone on top. Yet another one who suggests that. G.C. seems to want someone (qualified) to take responsibilty and sign off on it. I don't think is will happen anytime soon. I'm afraid if I say "just go ahead and let's do it" I myself would incur any liability resulting from this situation. There are too many other factors in the house that could be blamed on this. Any comments ??

[Rich]

:shock:
Where are you located at?

[maarass]

Thanks for the reply Rich. I located in Newark Delaware. Were about 300 feet above sea level. A neighbor 150 yards down hit a spring when he built his still standing house 20 some years ago. LOL.

[Rich]

Expensive out there.. I would keep looking for a geotech engineer that's a little more reasonable. If the GC wants someone to sign off on anything then it probably we be a bit more expensive as they'll be wanting to help pay for their insurance policy :)

[maarass]

Building costs are high here. Lots of Pharmacuitical companys, MBNA etc.. It's getting to be like silicon valley. Well it seems to be that popular concencus in this forum and another (alt.building.construction) as well as two experienced excavators, research I've read on the NET and two neighbors next to the lot with the same site conditions, is the layer of crushed stone. I got enough geofabric left over from the driveway to blanket the entire bed. Here's the funny part. My G.C. just heard from the soils guy (he just does site evals.) that the county is going to make suspectable site have a water table test done prior to getting a permit. WHEW !! Dont want the county involved. Thanks for all the replys.