Deep french drain + sump

[drmario]

So client's house was built at the very end of a large V-shaped granite ledge that (guess what) slopes towards the house. They tried to mitigate basement water issues over the years with all kinds of things (outside + inside) but still not satisfactory. Here's sketch of the overall topography:

We did some excavation and it looks like rocky strata is about 8'-10' down from the top of their lawn between the two ledges. So we're thinking at the moment of installing a very deep french drain with a sump pit to basically prevent water going towards the house. Anyone done something like this? Or any other suggestions?

 

[MTNClimber]

You now have to direct the water collected in the underdrain to discharge somewhere else, hopefully downgradient of the house. It can connect to a storm sewer or daylight where erosion/scour can be limited or avoided. This could be a lot of water, so make sure to take that into account. It would be wise to involve a local engineer with experience in these systems.

 

[dik]

Is this a warm climate (ie. no freezing)? Do you have to worry about the pump freezing? What is the amount of groundwater? Is there a chance for huge rainfalls, like the recent huricaine?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[drmario]

The project is located in Massachusetts -- so north-east USA. Typical frost-heave depth around here is 3.5 - 4 feet. And there's definitely area on the other side of the ledge where the pump can discharge away from the house.

 

[dik]

You need to determine the amount of water you will be 'draining', and enclose your clean granular material with a filter fabric.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik