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RE:basement uplift follies

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"Jeff Smith" <smthengr(--nospam--at)> wrote:
>A while back I posted some questions on a ski chalet basement. The
>retaining walls are over 21 feet tall on the high sides and the potential
>water table creates at least 14' of head. The project will only get to the
>ground floor before they cover it up for the winter. I have a net
>hydrostatic uplift of about 300 psf. so I need to fill up the basement with
>some counter balance.  I do not want to add piers because it will
>penetrate the membrane. So I am left with filing up the basement with
>about 5 feet of water. I am concerned that when the water freezes it
>will damage the walls. There probably will not be power to heat the
>water or to provide pumps. Alternatives include borrowing some chair
>lift counter balance blocks, caltrans lane dividers, or install water tanks.
Anyone have any ideas?

>I explained to the geotech that the basement was for a squash court.
>The geotech told me that he has played squash and that the game is not
>*that* great.

Do you have any plans for a drainage system underneath the slab or
behind the walls?  A properly designed and installed drainage system
can effectively eliminate the uplift forces.  Another option is to drill
shallow wells (30 to 40 feet) and install pumps in the ground outside of
the building.  I have seen this done for hydropower plants in Nebraska
that effectively reduce the phreatic level below the foundation of the
plant.  Of course, you will need to get power to the site to do this and
have someone regularly check the pumps and the phreatic level in the
wells.  Either way, this would eliminate the need to counter act the uplift
force.  The slab could heave if the water below the slab is not drained
away and it freezes, no matter how heavy the counterweight is.

I hope this helps.  Good luck.

Michael S. Davis, P.E.