# Retaining water and soil in excavation beneath water table



## BMRBrad (Jan 16, 2013)

Lets first clarify that I did not design this house and I agree that having the basement setup like this is placing a lot of faith in the back up power failure systems. The neighborhood it's going in the tall basement is a standard practice, we are just stuck with a really bad soil and water combination on a tight lot. If I had my way I would go 7' excavation, have main floor 2' above grade and sacrifice ceiling heights on first and second floor to stay under our maximum height build. But some people want what they want despite logical reason.


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## BMRBrad (Jan 16, 2013)

jmacd said:


> What state is this in? They will let you put storm water into sanitary system.
> 
> A wet basement sucks.


This is in Ontario near Toronto Canada. The city will allow an overflow in case of pump failure but it is not intended for full time use. In our case it wouldn't help because the floor slab is lower than sewer line so an overflow would run I to floor drains leading to an ejector pump. So the house in completely reliant on pumps. Not ideal, but we aren't the only ones in the area with this issue.


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## rino1494 (Jan 31, 2006)

BMRBrad said:


> Houses in the area have engineered weeping systems. Some places have 2 or more pumps. They have floor drains placed beside the sump pits with an overflow tube connecting the pit to the drain. If the pump does not run the water is drained off into the sewer system. I visited several homes being constructed in a mile radius. Water is an issue everywhere but the basements are dry with the weeping systems.
> 
> This house will need sump pumps and sewage ejector with battery back ups and high level warnings. Did I mention the sewer line comes in higher than our floor slab? Hence the sewage ejector... One day I will look back on this and shake my head.


I hope you are installing a backup generator.

If you really want to get expensive, you could do sheet piling. Or pile driving with H-beams and using wooden cribbing.


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## greg24k (May 19, 2007)

My apologies, I misread this post... somehow I thought this was about installing a footing for a retaining wall.

You shouldn't never have basement floor elevation bellow seasonal high water table. You will always have a moisture problem and mold issues. Your floor elevation should be minimum 1' above the water table.


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## BMRBrad (Jan 16, 2013)

The house will have a back up generator and battery back ups on the pumps as well as high level alarms. 

I'm meeting with the geotechnical engineer this morning. Ill keep this blog updated with what he suggests.


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## dayexco (Mar 4, 2006)

i'm fully aware, that soil conditions vary from where i live...to where you are, and codes/requirements are different. for the life of me, i cannot believe a lender, let alone a new homeowner....would want to finance/build a home, 3' into the water table? that this would not be a perpetual problem? why doesn't your local code jurisdiction say like it is here..."hey, you want to dig a hole....you dig a test hole first at the elevation you want , it stands for 48 hrs., no water,....no wait.....finish your hole...otherwise, you put the lowest elevation of that structure a min. of 1' above where the water stands....builders forget that fill is VERY cheap.


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## BMRBrad (Jan 16, 2013)

If the installation of vertical shoring proves to be too expensive for my clients taste, then reducing the foundation depth will be the only alternative.


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## Cuda (Mar 16, 2009)

Also consider water powered back up sump pumps. If the first pumps go and the batteries drain on the secondary pumps then the water powered pumps take over. They do not have the greatest GPM but could be just the right amount of help to get past a extended power outage.


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## BMRBrad (Jan 16, 2013)

Following up on this thread I started a couple months ago. We redesigned the house to sit higher than the water table. Despite it causing a three month delay in the build, it was the best over option logically and financially. The house will be built on helical piers with a grade beam footing heavily reinforced. This week we just started by putting in a trench around the excavation to control the bit of water that would be in the for work for the footings.


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## Redneckpete (Feb 22, 2008)

Brad:

We are very local and deal with this problem all the time. It really isn't a problem, dispite what everyone here is telling you.

I know the area, I know what you are dealing with.

Regarding the collapse of the excavation, we place geotextile fabric, then clear stone against the bank and your problem is solved. Groundwater can be pumped. Filter cloth around the base of the foudation solves sand infiltration.

alphaex.ca

Pete


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