Putting a drain pipe through a retaining wall

[Rockbadchild]

I built one small wall using fabric. Then I saw a video by a landscape contractor vehemently criticizing the use of fabric. It got be to rethinking the use on my second larger walls. I think landscape fabric is designed to lay on top of the dirt and let water through. If it is under the dirt I think it might clog up and act as a barrier and not pass any water.

And that is the problem with the internet. You can find someone to justify whatever you decide to do.

On my second wall, no landscape fabric, back filled with 2 feet of gravel, sock covered pipe at the bottom, several levels of geo grid. After a rain I evidence of water weeping out of all levels of the wall. I think that is a good thing, to me it means the water is not trapped behind the wall.

Doug in SW IA

Its opinionated driven... for disclosure I have a civil engineering background but it doesn't mean I am 100% right and it's not because he is a contractor that he is ether. If you notice in my illustration above the top is seal with clay to minimize water coming from the surface. The concern is ground water and water fallowing the wall and going under, I would argue that if the soil clog the fabric it will clog the pure stone and the pipe as well so the longer I can keep that clear the better it is... I didn't show it but the fabric should go down along the undisturbed soil (left looking at the picture) and the pure stone and up the wall to separate the stone from any fines. some pipe comes with a filtration sock on it but I usually still put fabric to separate fines and pure stone. Water eventually make it through any soil the one it has the hardest time going through is clay.

You can get away without fabric, not saying it's a must but to say its a bad idea I disagree... If doing it without fabric I would used screen sand (coarse beach sand) to make the separation around the pure stone. or simply pipe with filtration sock and sand around it. But I like using pure stone it had a lot of void and flow capacity if the pipe get clog and less chance for it to clog.

 

[D&D]

You want the water to run away from the wall and a place for the water to flow too, the illustration is how I would personally do it, now I am not sure if you want pure stone below the .

View attachment 832496

two slightly different things for me. I run the filter fabric vertically against the native soil, add gravel and pipe then pull fabric over to wall. On the drains, I install 2-45 with a short section instead of 90’s. This makes life way easier if you ever have to snake it out.

 

[Rockbadchild]

two slightly different things for me. I run the filter fabric vertically against the native soil, add gravel and pipe then pull fabric over to wall. On the drains, I install 2-45 with a short section instead of 90’s. This makes life way easier if you ever have to snake it out.

definitely a good way of doing it for the fabric and also the way I would do it... I forgot to show it in the drawing

 

[plowhog]

Q- is there any way to bend the rigid white perforated 4" drain pipe? Maybe heat it up a little?

I know there is corrugated black perforated drain pipe that is flexible. But I have heard it is subject to collapse and the corrugations cause sediment retention and buildup.

 

[D&D]

Q- is there any way to bend the rigid white perforated 4" drain pipe? Maybe heat it up a little?

I know there is corrugated black perforated drain pipe that is flexible. But I have heard it is subject to collapse and the corrugations cause sediment retention and buildup.

yes , you can. filling the pipe with sand and then heating is preferred to keep the pipe from kinking. Swimming pool and pond guys use a flexible pvc. You might consider going to a 3” drain depending on wall height.

Flexible PVC Pipe - Crush Resistant, Light Weight, Plastic Tubing made for S-40 Fittings

This Flexible PVC Pond and Spa Hose is a PVC Ultra-Flex Hose which is made for S-40 Fittings. Connecting is a breeze with any PVC Glue. Can be used for above or below ground installations. The Flex PVC Pond Hose has a Flexible PVC wall & cover.

www.flexiblepvc.net

 

[plowhog]

Swimming pool and pond guys use a flexible pvc.

That looks very flexible but does not appear perforated. Yes I am thinking of scaling back to 3" as my wall is only 100' long and while I expect run off, hopefully nothing that would exceed 3".

I am going to run a solid 4" pipe from the lowest point of the wall, perpendicular, under the wall, to daylight.

Where that "daylight" drain pipe emerges behind the retaining wall, I need to turn 90 degrees so it follows the wall, then add drain piping behind the rear of the wall. I have two separate thoughts:

1. Put an initial single section of somewhat rigid 4" perforated drain pipe behind the wall, connecting to the drain pipe that goes to daylight. This section would be at the lowest part of the wall, presumably handling the most water.

2. "Upstream" from that, "neck down" to use flexible perforated 3" drain pipe. Connect them together by simply shoving some number of feet of the 3" flex line into the 4" rigid perforated pipe.

This method of connection might sound funky but my excavator says he does it a lot. Having looked again at the open trench, there is not a lot of extra room from side to side, so I think 3" is a better fit for the majority of the run.

I am considering this for the 3" drain pipe:

Advanced Drainage Systems 3 in. x 100 ft. Singlewall Perforated Drain Pipe 03010100 - The Home Depot

Advanced Drainage Systems, Inc. (ADS) 3 in. x 100 ft. Singlewall Perforated Drain Pipe provides superior strength while its high density polyethylene (HDPE) construction allows the corrugated pipe to be a flexible, light weight solution for your outdoor drainage project. The pipe can be...

www.homedepot.com

 

[dstig1]

two slightly different things for me. I run the filter fabric vertically against the native soil, add gravel and pipe then pull fabric over to wall. On the drains, I install 2-45 with a short section instead of 90’s. This makes life way easier if you ever have to snake it out.

That is what I consider best practice for this too.

For bending PVC, a heat gun or a propane torch works. Keep it moving all around and when it starts to get soft stop quickly or you will have a pile of goo.

 

[Streetcar]

That is what I consider best practice for this too.

For bending PVC, a heat gun or a propane torch works. Keep it moving all around and when it starts to get soft stop quickly or you will have a pile of goo.

electriCal contractors have heat box for softening conduit to bend it

 

[dstig1]

Yes there are tools made for this job, and you MIGHT be able to rent one but otherwise they are hella expensive, especially for a one-time use. I have seen versions that are heat blankets, too. But for a one-time deal, heat gun or torch and some care will do the job, just not as easily.

 

[rScotty]

For 90 degree bends on large diameter PVC I don't mess with trying to make them. I buy preformed Sweep Ls or Combination Ts at Home Depot. I prefer the T shape - also sometimes called cleanout hubs - you can use them as a 90 by plugging one end. If you plug the end with a threaded PVC connection in similar large diameter, that gives you a way to root or flush out the drain pipe if you ever need to do so.
Instead of the slotted corrugated drain I use rigid PVC drain pipe with the drilled holes. Put down geotextile into the ditch, then some clean gravel, and then the PVC. Fold the geotextile over the PVC and backfill..... that way makes a better drain.

rScotty