I have a residential grade sump pump in my crawl space that has recently begun to run almost continuously due to the spring thaw. The house backs up against a hill that has expansive clay shale. We believe that the native water was traveling down the hill in the shale planes, and that the house excavation essentially severed the water path, so now the water ends up in our crawl space instead of traveling to regions unknown.

I pulled the sump pit cover and investigated the water source. It appears that all the water is coming through the bottom of the pit (i.e. high water table). Not a drip from the foundation drain pipes.

I am trying to head off a problem before it starts (i.e pump failure). So far I have looked at installing a larger pump and pit, but I feel like my pump is basically in a lake and all a big pump will do is pump more water. I will be investigating just turning the darn thing off and seeing if the hydrostatic head will balance, but then I get into another dilema with a moat sitting around my house after my house drain backs up.

The house is constructed on a grade beam/helical pier foundation system. I have been monitoring it via water level and the foundation is dead stable, but based on experience, having a lake around your house isn't exactly good.
Two options I can think of are 1) a deep french train or 2) a deep cutoff wall.

Either way, you'd need to dig a trench on the upstream side of the house.  I'd dig it at least two feet below the grade beam.  Offset it outside of the zone of influence from the house foundation (ten to 20 feet maybe?).

For the drain, put a perforated pipe w/sock in the bottom and fill the rest with gravel.  Either daylight the pipe on the other side of the lot, or connect it to some solid-wall pipe and then daylight it.

For the cutoff wall, dig a similar trench but fill it with slurry. The object is to 'turn' the water before it gets there.

You're going to have to make sure it extends far enough around the sides to keep water from 'end-running' the trench.Split case pumps

2011-05-30

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