French Drain 2

[wsu1coug]

I have daylight ranch style home, and the front yard slopes down approximately 10-15 feet for 30-40 feet before it reaches the front of my foundation at the front bedroom wing and front porch. During heavy rains (frequent in the NW) water pools near the front of my foundation and front porch. I have begun to research french drains, but have received conflicting advise. At this point, I am planning on digging a trench filled with a 2" gravel base, 4" perforated drain pipe, and covered with additional gravel, landscape fabric, and topsoil. The drain will slope to the side of the house, and then down the hill parrallel with the home and daylight below.

My main questions include
(1)How deep and wide to dig the trench,
(2)How far from my front foundation to locate the trench/drainpipe?
(3)Wether to install additional drainage improvements at the base of the hill higher up on the lot and furtehr from the house?

Some Points worth noting:
(A)The home was built in 1979
(B)The foundation at the front of the house is shallow (1.5 ft deep, but there is a deep concrete retaining wall further back on the house.
(c)The soils appear to have a heavy content of clay
of my home is located below street grade and the lot hillside

Any advise would be really appreciated!

 

[BigDog23]

At first glance, unless I misread the statement, is that the real problem you are having is caused by the heavy clay soil. The french drain wrapped in mirafi will be only has good as the percolation rate of the soil surrounding it. So pulling out the clay soil and backfilling around the drain with your suggested grave then sand would be ideal. This is all to make the drain functional.

Another alternative would be to regrade the landscape, providing a landscape swale around the perimeter and discharging down the hill parrallel with the home. Alot of time when grading lots with drainage from back to front the landscape swale is provided, but over time and homeowners they slowly get filled in, then creating puddles. So it may nearly be that the landscape needs to be reworked to emulate the orginal intent of the lot. Not alot of fun though because I imagine your landscape is set and you probably don't want to dig it all up, but then again it is the best way to remove the standing water and assure yourself there wont be any additional flooding.

HTH

BD23

 

[gibfrog]

Bigdog is correct on two major points, the french drian is not a ideal solution and it is usually cheapest to regrade to a new diversionary swale and move the water away from your house and downhill.

The french drain could work if it is installed at lowest area and you leave the rock/gravel exposed. However, it will be a continual maintenance nightmare and as silt/clay wash into the gravel, the percolation rate will be reduced. Eventually the gravel will need replacement, once it plugs up.

Another alternative is a series of small plastic catch basins suitable for pedestrian and lawn tractor traffic with 8" corrugated polyethylene plastic pipe such as ADS, NDS locatede at low points. Try to maintain 12" of properly compacted cover over the pipe and a minimum slope of 1% (less is you can accurately lay the pipe, but more is better until your outlet velocity is excessive and causes erosion.) End the pipe at a 4" concrete mitered end wall to a swale to daylight or a spreader swale. You could end the pipe at a bubbler (a catch basin that flows "backwards, but this will be a maintenance hassle.)

You could always high an engineer to properly design your system or waste $5,000 like my neighbor did. He had his buddy, a "grading contractor", improperly install a system that needs lots of maintenance and functions poorly. Clifford H Laubstein
FL Registered PE 58662

 

[gibfrog]

Bigdog is correct on two major points, the french drian is not a ideal solution and it is usually cheapest to regrade to a new diversionary swale and move the water away from your house and downhill.

The french drain could work if it is installed at lowest area and you leave the rock/gravel exposed. However, it will be a continual maintenance nightmare and as silt/clay wash into the gravel, the percolation rate will be reduced. Eventually the gravel will need replacement, once it plugs up.

Another alternative is a series of small plastic catch basins suitable for pedestrian and lawn tractor traffic with 8" corrugated polyethylene plastic pipe such as ADS, NDS locatede at low points. Try to maintain 12" of properly compacted cover over the pipe and a minimum slope of 1% (less is you can accurately lay the pipe, but more is better until your outlet velocity is excessive and causes erosion.) End the pipe at a 4" concrete mitered end wall to a swale to daylight or a spreader swale. You could end the pipe at a bubbler (a catch basin that flows "backwards, but this will be a maintenance hassle.)

You could always hire an engineer to properly design your system or waste $5,000 like my neighbor did. He had his buddy, a "grading contractor", improperly install a system that needs lots of maintenance and functions poorly. Clifford H Laubstein
FL Registered PE 58662

 

[boo1]

Of course these guys are right, but I can offer you a theory (Double) that I have found works. Just keep the basic principles clear and double what others recommend: It's a trench to catch and divert water. Ideally, it could be a wide open trench, but that's usually not practical, so you want to fill it with material that will still let the water move through it and that will keep crud from plugging it up.

We dig the trench at least 36 inches wide and 16 inches deep. The slope of the pipe is crucial to the success of your French drain. So the grade is very important. The trench should slope at least 1/8 to 1/4 inch-per-foot towards its outlet. Lay geotextile, a permeable non-degrading fabric leaving enough to overlap 12 to 18 inches at the top. Spread two inches of gravel or rock (3/4 or 1.5 inch) on the bottom. Locate and install two or three collection boxes as appropriate. Then lay two or three 6” perforated drainage pipe (function of runoff flow) wrapped with SOCKS in the bottom. If the pipe is perforated on one side install with the holes in the lower side. . Tie the collection boxes into only one of the pipes. Then fill with crushed stone to about 6 inches from the top. I put about 2 inches of pea stone next (small crushed stone). Over lap the geotextile fabric and back fill with coarse mason sand.

Additionally consider guttering the run off from the house to the drains.

 

[Chris73]

Since I have seen quite a few drainage systems I can recommend boo1's solution and measurements. Only I see no reason to put 2-3 drain pipes into the trench. Estimate the amount of water to choose a pipe size but a gut feeling tells me that 6" should be big enough in most cases - considering that the surrounding gravel can drain a lot through its pores. Either you lay the perforated pipes hole-down or you might consider scraping a groove as big as the pipe and as deep as the non-perforated pipe section into the clay bottom of the trench and lay the pipe hole-up. That enables a faster discharge of the water due to better hydraulics. Don't forget to overlap the longitudinal joints of the geotextil as well.

 

[boo1]

The reason I like to use more than one pipe is to separate the collection boxes from the collection line. This adds redundance, and the pipe is cheap. So for those who don't do the hydraulic calcs and design, overkill works. This "theory" was taught too me from an experanced (>40 yr) concrete foundation mason. As a builder and ME I found it works.

Cheers

 

[dec4trax]

I agreee with boo1, as I installed 3 pipes in my french drain. It works great if you are a do-it-yourselfer, but no engineering firm would recommend it in a formal design. The benefits are that the multiple pipes are much cheaper than the gravel, it significantly reduced the quantity of gravel you will need to shovel into the trench, and it creates lots of annular space in the trench to facilitate drainage. Only the bottom pipe will actually transmit flow. My f-drain has been working well for the last 8 years.
Its one of those things that theory cant support, but works well in real-life situations.