# Drainage ? for an 8' tall Retaining Wall



## White Elk (Jul 27, 2008)

We've got an 8' tall retaining wall which is holding back a large hill. We live in a wet climate and alot of water comes off that hill, which then gets behind the wall. But there are weeps all along the base so that the water evacuates freely. (_pics below_)

However, I am going to build a planting bed along the wall. By putting dirt in front of those weeps, I would be impeding the water flow. I am concerned that impeding the water will allow it to back up behind the wall, which will eventually bring it down. 

My plan is dig a trench along the base of the wall and install drain pipe, bedded in gravel, which is covered with drain cloth. Then above this gravel trench I would mound the gravel up to cover the weep holes. And cover it with drain cloth. Then I'd build a 2' planting bed wall a few feet off the retaining wall, and back fill it with planting soil.

*Do you think this would work?*












*What grade of gravel would be best? *

*And do you have any advice as to which type of drain pipe and cloth I should use?*













Water constantly drains out these weeps.


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## 47_47 (Sep 11, 2007)

That's a tall retaining wall to dig near the base. I'd be concerned of an avalanche and consult with an engineer.


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## concretemasonry (Oct 10, 2006)

Since that is an older style tall rigid reaining wall instaed of a modern segmental retaining wall you will have a spread footing since things will not be what you show on the sketch.

You can measure the height of the wall face, but it is also holding back a large portion of the sloped soil behind and above the wall.

If it was a typical DIY wall, you have a small footing and the likelyhood of problems is greater than if it was engineered.

Dig a little in a couple of spots to determine what you have to support the wall.

Dick


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## White Elk (Jul 27, 2008)

I've been wondering that same thing! My thought was to work in 6' sections and backfill 4' of it immediatly. And also to use some 2x6's for support (braced against the wall and nailed to posts driven in the ground). We are tight on money but the 2x6's are leftover from another project and will later be used for a chicken coop. But perhaps I can rent some better braces cheaply? Has anyone ever done anything like this before?

I'd prefer to dig the full length of the trench, then lay the pipe etc. But risking wall damage or my early burial makes me think of playing it safer. Once its done I think the compacted gravel will be more stable than the dirt. But then my expereiance is all in labor and not structural considerations like this. So I need advice on this part of it as well.


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## White Elk (Jul 27, 2008)

concretemasonry said:


> Dig a little in a couple of spots to determine what you have to support the wall.
> 
> Dick


Will Do! And then post the pics.

I think the wall is at least 50 yrs old. I know it was built by my neighbor when he was young (he built this house and raised his family in it till his divorce, his ex wife got the house.. he parceled his land and built a home nextdoor). He was a commercial builder but not very experianced in his youth. So I guess it could be considered a DIY wall. It's been so long that he doesn't remember some of the details of things.


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## Bud Cline (Mar 12, 2006)

I wouldn't dig out anything for fear of compromising the stability of the footing that is there now - whatever it is. Leave all of that in its virgin state.

You can still do as planned and drawn. I think that is a sound concept.

Build the new wall, and port the bottom joints basically the same as what was done with the taller wall. Install crushed stone size:3-4 up to the weeps in the old wall. Lay in a perforated drain pipe lateral same as used in leech fields. Allow the drain pipe to penetrate the ends of the new walls on either end. What you do with that run-off is up to you. (Should there be any.) Then add some additional crushed stone size: 3-4 about four inches above the drain.

At that point the crushed stone can be covered with two layers of the Phillips landscape drain cloth then filled with soil above that.

During wet conditions there is a tremendous amout of pressure on that wall. I wouldn't do anything that would have an effect on the existing footings or foundation.


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## Gary_602z (Nov 15, 2008)

Since the water and pressure is coming from the up hill side is there any way to put a drain such as you are thinking of on the high side? I would have it run to the right side of the picture that you showed. Then just up hill of that I would berm it to run off some more of the surface water in the same direction. Is the wall leaning some already or is it just the picture?

Gary


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## concretemasonry (Oct 10, 2006)

I suggested to dig in a few local spots to find out what you have. If it 50 years old and still appears sound, it probably has a footing. You should find out how deep the footing is and far the spread portion sticks out into your yard.

Do not dig below an imaginary line estending out from the bottom of the footing at a 45 degree aniamal since you could be reducing the strength of the footing bearing and the resistance to siding.

The idea of a drain with cloth and rock is a classic method if you do not upset the original stable construction. A failure can be rapid and dramatic if the soil is saturated. The tree growth and the vegetation make sure the water is absorbed in the soil and does not just run downhill and over the top of the wall.

Dick


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## joed (Mar 13, 2005)

I don't think I would dig at all. Just clean up the bottom of the wall to a level surface and lay your pipe and gravel as in the diagram.
I don't see any advantage to digging down in front of the wall.


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## Wildie (Jul 23, 2008)

I would suggest that you would build the new bed. lay the drainage tile in the bottom, near the old wall and then cover it with gravel.
Filling it up, the rest of the way with top soil.

It appears that your neighbor did a good job of the wall, as it has retained the hill for this long!
Excavating probably wouldn't cause a problem, but why tempt fate, if its unnecessary!


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## White Elk (Jul 27, 2008)

concretemasonry said:


> I suggested to dig in a few local spots to find out what you have. If it 50 years old and still appears sound, it probably has a footing. You should find out how deep the footing is and far the spread portion sticks out into your yard.


There is a 4" slab (_at the thinnest point I found_) of what I'm certain is poured concrete. The top of this footing runs level with the ground. There is no spread beyond the face. I also trenched an inch deep for 13' and saw no seams. Under the footing there is an inch or so of dirt and then a sandy clay. It is saturated (_but all our ground is_). Which actually might be a good thing since theres so much sand in the soil?




















Above is a better shot showing the elevation and hill slope. Beyond that crest is a gentler slope and then a greater slope for near 60 yards to the tree line. Alot of water comes down that. The Cedar tree and the decidious are gonna need to come down. I found cedar roots growing through some weeps. There is a bunch of Ivy still on that hill (_it used to cover the wall_). And I'm still fighting the blackberry there, but I've nearly won that battle. I will wait to remove the ivy until spring so as not to make the slope barren. LoL I have plenty other blackberry patches and nettle root systems to battle this winter anyway.


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## White Elk (Jul 27, 2008)

Bud Cline said:


> I wouldn't dig out anything for fear of compromising the stability of the footing that is there now - whatever it is. Leave all of that in its virgin state.
> 
> You can still do as planned and drawn. I think that is a sound concept.
> 
> ...


Thank you for the detailed info and the specific material suggestions!

What do you mean by "_port the bottom joints_"? Below is a pic of a small retaining wall I built adjacent to that big retaining wall. I'll be using the same material. I set the bottom row 2" below ground level at its lowest point and leveled as I went. At the highest point, the bottom row is just below the surface. Under the wall is a 4-6" deep gravel bed (_with no drain pipe_) which rests on clay. It is sloped away from the big retaining wall to encourage excess water to flow out of the backyard (mighta been unecessary?).


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## White Elk (Jul 27, 2008)

Gary_602z said:


> Since the water and pressure is coming from the up hill side is there any way to put a drain such as you are thinking of on the high side? I would have it run to the right side of the picture that you showed. Then just up hill of that I would berm it to run off some more of the surface water in the same direction. Is the wall leaning some already or is it just the picture?
> 
> Gary


This is on my project list for late summer 09. I think it will help, but will not allow me to forgoe the base drain. I want to build a gravel path there so I can move a heavy wheel barrow across as needed. This gravel path will also reduce some of the landscape maintenance along the top of the wall. My plan is to drain it to the left side (to the right is a garage and above it is a rising slope). Then tie that drain into the base drain and run it all down the side yard and down into a little bog below the front of the house. LoL I have wondered about having it flow into the waterfall that I have planned for that left hand corner. Then construct the pond to overflow into the drain as needed. But I think it may be better to run the drains seperate, and then tie in below the pond.

That wall is leaning top side. Good eyes. 
In 4*'* there is up to an inch off level.


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## White Elk (Jul 27, 2008)

joed said:


> I don't think I would dig at all. Just clean up the bottom of the wall to a level surface and lay your pipe and gravel as in the diagram.
> I don't see any advantage to digging down in front of the wall.





Wildie said:


> I would suggest that you would build the new bed. lay the drainage tile in the bottom, near the old wall and then cover it with gravel.
> Filling it up, the rest of the way with top soil.
> 
> It appears that your neighbor did a good job of the wall, as it has retained the hill for this long!
> Excavating probably wouldn't cause a problem, but why tempt fate, if its unnecessary!


Do you guys think that will pick up enough of the water? The water drains out the bottom of the weeps which are 8" tall. Wouldn't some water still back up behind the wall if I put the pipe at ground level? 

Perhaps it would be better to install the pipe with half its diameter underground? 
And place it a couple inches out from the wall face, with the trench sloping 45 degrees away from the wall face?


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## Wildie (Jul 23, 2008)

White Elk said:


> Do you guys think that will pick up enough of the water? The water drains out the bottom of the weeps which are 8" tall. Wouldn't some water still back up behind the wall if I put the pipe at ground level?
> 
> Perhaps it would be better to install the pipe with half its diameter underground?
> And place it a couple inches out from the wall face, with the trench sloping 45 degrees away from the wall face?


 You could clear the topsoil of the top of that 4" footing! Then lay weeping tile on top of the footing, then backfill it.

You don't say, but frost doesn't seem to be a factor in your area.
With such a shallow footing, I would expect the wall would have failed by now, if you have freezing!


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## White Elk (Jul 27, 2008)

It does freeze here, but not alot. Though the weather has been trending towards colder these last few years.

The footing does rest on a sandy clay soil, with just a small layer of dirt. Perhaps that helps?

The footing doesn't extend past the face of the wall. The wall and the edge of the footing are plumb to each other. And for the most part, the top of the footing is level with the topsoil.




Wildie said:


> You could clear the topsoil of the top of that 4" footing! Then lay weeping tile on top of the footing, then backfill it.
> 
> You don't say, but frost doesn't seem to be a factor in your area.
> With such a shallow footing, I would expect the wall would have failed by now, if you have freezing!


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## Bud Cline (Mar 12, 2006)

By "porting" I meant to leave out vertical mortar joints to allow water behind the new wall to drain, the same as you see in the old wall. That was when I imagined you were building the new wall with concrete blocks. I see now you probably intend to use the stack-blocks (retaining wall blocks) and they are self draining so not to worry.

If you were to bury the drain pipe in the virgin soil you would force the draining water to percolate into the soil. This would be a much slower and possibly disturbing process than allowing the water to drain away at surface level via the ends of the pipe. Drainage will also come automatically through the retaining wall blocks.


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## chad4290 (Nov 28, 2008)

i would have it come out in the same spot as above. same weep holes in the front.just keep them open using a the same concept with fabric and 3/4 stone or similar. you could also use a pipe and just kind of divert the water right underneath and through the bottom front. i always use geogrid when working with block also. when that wall gets too bad or have some extra money you are going to have to fix it. if you do, the materials there are now and drainage techniques should hold that wall for the rest of your life and some.


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## White Elk (Jul 27, 2008)

Bud Cline said:


> If you were to bury the drain pipe in the virgin soil you would force the draining water to percolate into the soil. This would be a much slower and possibly disturbing process than allowing the water to drain away at surface level via the ends of the pipe. Drainage will also come automatically through the retaining wall blocks.


As things are now, the drainage between the wall and house is very poor! So the ground is heavilly saturated for much of the year. I would think that the saturated ground slows down the water flow behind the wall. Which allows the water to back up behind it, and increase the hyrdostatic pressure which will eventually bring the wall down. 

Long before the idea of a planting bed... I'd been thinking that the base of the wall must be drained. And now with a planting bed to cover the weeps, I think the drain becomes far more important? I think the planting beds dirt would further slow down the water trying to evacuate from behind the wall?

I can't slope the backyard to drain away from the wall, because it would run to the basement (_I'm currently trying to abate basement moisture already_). Nor can I slop it out the sides due to a detached garage on one side, and a hill on the other. So I must install some french drains to move that water out of the backyard. And with all things considered, It makes sense to me to also install a drain right at the retaining walls weeps.


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## White Elk (Jul 27, 2008)

I've been thinking on this retaining walls drainage problem a bit more...

Trenching right along the footing does seem like a very bad idea! 
Dicks idea of sloping the trench wall away from the retaining wall makes far safer sense. 

And now I'm thinking of moving the trench and drain all the way out to the planting bed wall (2-3' off the retaining wall). With a very gentle slope leading from the retaining wall down into the drain. Then adding a layer of drain rock on top of that slope. In this way the water would take the path of least resistance and flow out of the wall, down the gravel bed slope and into the perforated drain pipe. Which then daylights out to a bog in the front of the property. 











But... that solution (above) will exponentually increase the amount of material and time required. 

And the weep holes (slots rather) are 8" tall. The planting bed will be about 18" tall. So dirt would migrate into the weeps from the planting bed. As the weeps clog, the water flow would become increasingly impeded. I could attach some drain cloth along the face of the wall to cover these weeps. But I'd have to attach the fabric to the wall with some type of concrete fasteners. 

Since I'd have to fasten the cloth to the wall... I thought "*Well why not just attach the drain to the face of the wall?*" thereby saving all that gravel bed business. I've been googling around the net and have thus far only found one product for this (_I'm sure there's gotta be other products out there_). And I have yet to find a local distributor for it. 

*Does anyone have any experiance with **J-DRain** or other products like it?*


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