pooling water at foundation; replace slope with dry stack retain wall

[PineBushStoneMason]

I am in need of some advise as I am getting conflicting answers from contractors. My home is 2 years old and was built on former wetland in Pine Bush New York (Orange/Ulster County lines). There is a slope (rise =3' to 4' foot high; run = 8' to 12') that ends (wrapping around 2 sides of a cement patio) directly onto the rear cement patio that has a deck built above it. Water runs directly at the left side of the house, at the patio, and then pools directly behind the house where the steps from the deck lead down and then all the way to the right side of the house. The slope is parallel to the house along the entire back side of the house, but is closest to the cement patio. The ground where the water pools is clay, but the earth that is behind the slope seems to be very porous so that when water falls on the flat surface on top of the slope, it seeps into the soil but then hits clay and then what is not absorbed, runs horizontally to the base of the slope where is continues to pool up, thus I am dealing with pooling water from rain and also from ground seepage.

My fix was to have the slope cut out to a decent size back from the house so that the soil can be graded away from the house towards the base of a dry-stack stone wall that is to be placed in a concave shape (2'widex3'high'50' long) to retain the cut out slope/bank. French drains were to be placed in front of the wall approx. 18" from the wall base. (However, I did just read oon this web site that placing French drains in front of the wall is a bad idea?)

The French drain/retaining wall idea came from consultation with a landscape architect and were to run the entire parallel length of the back of the house wrapping around both house sides to daylight another 50 feet towards the front following the natural grade of the property.

I am scheduled to have this work done in two days so that the driveway can be put down on Monday 9/15/03. I would greatly appreciate all advice as I am looking for a permanent solution to this water problem. Thank you all so much. Jordan

 

[cvg]

hydrostatic pressure behind the wall needs to be relieved. Does your wall have weep holes?

What about the water sheet flowing down the slope? Is it being diverted, or will it flow down and over the wall? The french drain might handle it, but it may be better to divert it around the house.

 

[PineBushStoneMason]

Hi CVG, Thank you very much for your reply! As far as weep holes in the wall are concerned it is my understanding that dry stacked stone walls do not require weep holes as there is no mortar to prevent water from draining. The cut bank where the wall will be built is concave and will be lined with landscape fabric and then the wall will batter back one inch per foot and is backfilled with stone. Since no footings are required with dry stack stone walls there will be a base of stone two inches thick and the base will be cut 2 to 4 inches below the final grade in front of the wall, ( making the first run to stone somewhat below final grade) so should the drain also be placed in front of the wall at the base or placed out from the wall say a foot or so? The landscape architect who recommended this design mentioned that the wall should not fail due to the added strength of it being concave, as well it will have a two foot thick base tapering up to 1.5 foot. overall dimensions are 2' thich/wide, 3'tall, 50'long.

As far as water sheeting over the wall, the earth behind the wall is fairly porous down to the level where the base of the wall will sit, that ground then becomes clay so water flows down until it hits clay at depth of 3.5 feet; then it travels forward towards the bank/stone wall base and also flows towards the base of the slope as it is now.

I can email a photo of the site if that would be more useful, however you think, you have been a great help, so thank you again thus far
Jordan

 

[cvg]

make sure your "landscape fabric" is designed for drainage. It needs to be able to pass water, while retaining the soil behind the stone wall. Otherwise, you will still build up hydrostatic pressure on the wall.

Depending on the watershed area and soil type, this may work, however, the quantity of water and peak flow rates can't be calculated with the info you have provided. French drains can't handle large volumes of water or high peak flows. A swale or ditch with sufficient capacity to carry the water around the house would be the best method.