Starting a 28X32 with loft. Need advice with water challenges.

[Nick D]

Hello all,

I have a project underway and before I can spend the time creating a proper thread in the garage gallery I am hoping to get some advice about water around the excavation site. We dug 4' down for the footings and started getting water accumulating about 1/2 through the dig. When finished it was about 4" deep. Let it sit over night, came back in the morning to a hole with 20" of water.

I currently have two 1/3hp sump pumps rated at about 40GPM each relieving the hole of water.

I can see the level going down, but here is my problem. There is clearly water flowing into the hole. Enough that if I turn one of the two pumps off, the level slowly rises again.
3 days ago (day of excavation) we did get 1/2" of rain, but nothing really since. I have heard stories of people coming across underground springs in this town, so it doesn't surprise me that I have this type of water issue.

So lets say I manage to dry it out enough to get the foundation poured, (Footing + Frost Wall) what kind of issues can I expect to have in the future with high volume of water (likely underground spring) flowing next to or perhaps below my footings?

Thanks in advance!

Nick D

 

[blkhonda1991]

it seems like your water table is really high if that is what you are getting 3 days after a rain. is a floating slab an option allowed by code where you are?

 

[kbs2244]

I belive in saving money and DIY as much as the next guy.
Buy sometimes you have to buy the knowledge and experience of the pros.

At the least I would talk to your building department.
Your tax dollars pay for them.
And they should know about the area around you as well as your lot.

Then have a concrete guy with a good reputation do the work.

A good foundation is an absolute requirment.
You need to do it right even if it puts a dent in the budget and a delay is needed.

 

[Nick D]

Floating slab is acceptable as long as it has Engineer sign off. Thanks for the tip to contact the Building Department.

I initially contacted a local Engineering Consultant who was more interested in convincing me not to do a floating slab than taking my money. The economy can't be THAT good, can it?! I may have to revisit that option if I can't control the water in the hole, or if the building department has no good information to offer me.

I am fairly sure I can dry the hole out and continue on. I am hoping to get the opinions from GJ members who are confident with foundations. Should extra work (precautions) be done to compensate for what appears to be flowing water and a high water table??


Thanks,
Nick D

 

[theoldwizard1]

If you put drain tile in, is there any low spot for the water to naturally flow ?

 

[78Bird]

Any way to dig a drain trench to let it run off and get a good look at where it's coming from?

If you did hit a spring it might be possible to dig down more then plug it with something impermeable or divert the flow.

If it's general water table.... I dunno.

 

[wssix99]

You may want to look at a drain tile equipped with a sump pump in the finished building.

 

[70redbee]

You need to dig it down about another 2 feet and fill this with large gravel. Cover the gravel with a geotech fabric.Pour your footings like normal with 2 pcs of rebar. Once the stem wall is built lay draintile around the perimetor of the structure and run to daylight. I have built many houses like this and never had a problem. You just need to get the water away from the building. If not able to daylight just put in a pit with a sump pump. Good luck.

 

[Nick D]

Thanks to all who have replied.

A small update.
I have managed to get the water level down to less than 2". After speaking with a local builder, I have decided that the issue is a high water table, and that I picked a bad month to dig a hole here.

Here is what I am thinking:
-Dig deep hole in corner (out of the way of footing forms) for sump pump.
-Bring the level up in the base of the hole, about 4-6". This should get me up out of the water.
Yes, this will raise the building up, but I am planning to bring grade up anyway, so another 6" isn't going to spoil things.

I don't think I need to dig deeper and bring more fill in. The base seems very solid. The material is a sand gravel mix with larger stones about the size of a fist.
I am also not sure draintile will improve the situation, especially because I cannot daylight it. If the issue is a high water table, the tile could potentially be submersed from end to end when the rain falls in large amounts and in my mind, that means no flow.

For a little more background, we have never had standing water on the property, no matter how much rain we got.

My question now is can I fill the hole back in with the material I removed, or would a fresh crushed stone of some sort be a much better base? Do both of these materials need a compactor run on them? I am told the vibration may bring the walls of the excavated hole in? Am I way off in thinking that I shouldn't concern myself with draintile?

Thanks again for the advice.

 

[NickD]

This is just a follow up post in case anyone in the future happens to be in a similar situation and is looking for options.

I contacted a Engineer who provided a new footing design to compensate for the active and high water table.
The details are:
- Increase width of footing from 20" to 24"
- Increase rebar runs from 2-1/2" to 3-5/8" runs
- Prepare the base with no more than 6" deep of 3/4" Clear stone. Stone must be tampered, also must have geotextile fabric (landscaping material) beneath the stone.

Some pics of the progress.

Thanks Again for the input.

 

[Rosco]

looking good. Very smart to come on here and post for suggestions in the middle of the project.......that takes patience!