# French Drain in CLAY



## LNG24

OK CLAY Experts. I never had this happen to me before, luckily this was on my property. Put in a French Drain. Wrapped the entire trench with Filter Fabric. It failed. Fabric clogged up and stopped taking water. Had to tear open the top of the fabric to allow the water to get into it. 

A friend of mine had the same problem only it was on a huge job. They called in an engineer and the engineer told them NOT to sue filter fabric in clay. Instead use Rip Rap topped with 3/4 and bring it right to the surface.

Now if I read this post I would argue that the clay will clog up that trench, but I witnessed first hand the problem with the filter fabric. 

So let me hear your opinions.


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## cleveman

how's your friends application holding up?


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## threaderman

That actually sounds about right.Due to the loose/fine soil in Florida and Vegas,I always used the "socks".In Chicago and Oklahoma where there is more compact type soils/clays,the gravel method works very well.


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## rino1494

Definitely, filter cloth gets clogged up quick and doesn't allow the water to flow through. With french drains, we never wrap the entire trench is fabric. Just the install the rock and cover the top with fabric then backfill.


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## denick

I wish I could find the article I read once about the use of coarse sand as a filter when in silty or clay soil. The engineer made a good case.


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## Alan Mesmer

Lots of clay in my area of NE Ohio and I almost never use fabric. Usually just use #57 to surface on top of perf pipe. The only exception is when I am going through tree roots, I always use fabric to keep the roots from filling the pipe solid as they look for water.
Alan


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## cexcavation

I deal with a fair amount of clay in my area, and based on my own logic (which isn't always a good thing:blink I run 1 1/2 open all the way up until about the last 12". I throw down the old school "builders paper" on the top and then back fill. By the time the clay settles and glues itself back together, the paper is already started to decompose and eventually won't be part of the equation. Due to the sides of the trench already being compact, there is no need to try and deal with them. The clay doesn't really move except for the sediments from moisture seepage. (this is where the plugging of fabric gets you in trouble) I run the 1 1/2 partly due to ease of installation and grading, pipe protection, and again my logic seems to think there is less chance of major erosion causing soil to fall into the larger voids of the "rip rap" or 6-8" open or whatever. I also say the more rock the better, since french drains are not fool proof and you really need to look at them in terms of an underground moats where sediment is inevitable and storage capacity is on a steady decline as time goes on. I usually try to put cleanouts in the actual pipe so that the customer can flush the system before going into the drier seasons. Again this is all just on the fly logic, so take it for what it's worth. If I were an engineer then I would have way more money in my pocket, but be bored out of my mindarty:


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## pottsgroverc

If there is a lot of clay in an area, typically french drains are not required because the ground really doesn't seep a considerable amount of water anyway. Then, you are only trying to pick up surface water. In which case you can just use area drains. I have found the french draining, or underdraining, usually only works well when you have a soil that percs well.


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## denick

Here we are with the regional definition of some type of construction.

French Drain, The definition I found a long time ago is "a trench filled with rock" thae is the technical description. No pipe, no cover. the surface is sloped to the drain. These were field drains for surface water and intercepting any ground water to the depth of the drain. Basically to dry fields for crops and to control water flow.

Now???


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## cexcavation

I agree with Denick

I rarely install "French Drains" since people are modifying their original purpose and asking them to be a permanent fix for situations that don't really apply. I put in french drains as a last resort-usually if the previous excavation contractor or homeowner didn't slope things properly. Alot of the saturation issues are a result of "pooling" surface water rather than groundwater from an alternate source, i.e. springs, etc. Most people think that a french drain has some sort of magical water magnetism property that sucks any water out of the ground within a 1/4mile radius:laughing:


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## Blas

I have done quiet a few projects with french drains last one was a high school parking lot about 10 acres with a 900 long drain down the middle. The engineers up here are using contech rigid PVC draintile wrapped in 4 feet of pea gravel wrapped in filter fabric covered with 1 foot of 3/4 inch clear rock and 2 feet of sand. Above the sand is the class 5 base for the parking lot.:thumbsup:


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## LNG24

THANKS for all the great replies. Well I can tell you for sure that my method FAILED and they had to redo theirs and its working as far as we know, no call backs yet on his second attempt. 

I think only two of you mentioned it: So my final question is this: Pipe or No Pipe? Here's my problem with No Pipe. I have to pipe it (well maybe not) to a storm drain. I can get 6" of cover over it if I run it with no pipe, but I think I'd have more maintenance keeping the gravel exposed. 

I am thinking I should pipe the last 20' of Open Trench and then another 10' where I am covering it to kind of choke it and force it into the pipe. 

As far as the use or purpose of this. No all homes are built to allow for proper drainage. In my case the foundation has good pitch away from it, I am trying to protect the yard, Stairwell and deck from BOTH Surface runoff (And boy does it run fast over that clay) as well as below surface "veins" since the yard is on a good slope, I get some veins of water popping out of the hillside. I already have an OPEN trench (no gravel at all) along the entire back of the property to catch run off from the farm behind me, but I get a tremendous amount of water that is coming right out of the hillside do to these underground veins. 

So our new idea is to pull up the existing French Drain, Dig it deeper and extend it up the hill further and create a dry creek bed look, though it will be fully functional.


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## cexcavation

LNG,
If you can identify the source then a single drain/creekbed system should work by redirecting the flow around the area you are trying to protect. But like Denick mentioned, if the whole area is saturated with no real source, then grids of drains like in a field would be necessary....at least I would think. As far as perf pipe, I always use it since I can set it to grade, I know that it will always be there, and it contains the water once it enters my "trap". If you have a dump point, i.e. storm drain, ditch system etc. then you can run the perf clear out, otherwise you can stop it short and let the remainder of the ditch (that is outside of the affected area) act as a dry well of sorts. All my opinions with absolutely no scientific data to support!!arty:


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## Duff

I always use pipe whether french or curtain. Trench, 3" base of 3/4", 4" PVC perf pipe, topped off with 6" of 3/4" then fabric. Checked last years jobs this spring after wet weather and seeing good flow.


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