Boulder retaining wall erosion!!

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  #1  
Old 01-11-08, 12:47 PM
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Join Date: Oct 2006
Location: Madison Wisconsin
Posts: 68
Boulder retaining wall erosion!!

Hi all,
I have a boulder retaining wall in a home in southern (Madison) Wisconsin we bought a year and a half ago. As you can see by the photos Iíve posted we have an erosion problem that needs to be addressed near the largest center boulders. The black corrugated tube above the top boulder is drainage from the downspout which comes down from the edge of the garage in the top center of the photograph below.

http://s264.photobucket.com/albums/i...t=IMG_0656.jpg

The black drainage tube is buried underground and comes out just above the boulder. Over time the rainwater discharge of this pipe has eroded the earth around these large boulders.

Close up of boulders and downspout

http://s264.photobucket.com/albums/i...t=IMG_0657.jpg


http://s264.photobucket.com/albums/i...t=IMG_0658.jpg



My questions are as follows:

1) What can I do in this particular situation to rearrange the downspout ?

2) What can I do (what should I use) to fill in around the boulders once the drainage tube is rearranged?

I want to get this situation corrected on my own (if I can) before so much erosion and boulder movement take place that I have to call professionals in to rearrange the boulders.

3) I have other small retaining walls that are similar to this and are experiencing similar (but much smaller amounts) of erosion between boulders. What should I be using as fill in between boulders where earth has eroded? Should I be planting some sort of earth holding groundcover as well in the cracks.

Thanks for any and all thoughts regarding this situation.


Cheers,
wvdthree
 
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  #2  
Old 01-12-08, 03:33 PM
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Location: USA
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Remove boulders at end of drain. Dig ditch and extend drain into area in from of retaining wall. Tie drain into storm sewer or install a French drain to accommodate water from downspout.

The mortarless retaining wall system is appropriate for low retaining walls. The success of retaining walls is dependent on the drainage behind the walls. Folks typically dig a ditch about a foot wide and two feet deep parallel with the wall and up the slope from the wall, filling in with gravel. Next, a slotted drainage pipe is placed in the ditch, filling in with gravel and covering with landscape cloth, before covering over with soil. The ditch containing the drainage pipe can be directed to the storm sewer or a French drain. This methods help direct water moving toward the retaining wall to another location.
 
  #3  
Old 01-19-08, 09:25 PM
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Join Date: Jan 2008
Posts: 5
Here is what I would do if someone called my company. I would re-route the tile so it goes between the timber steps. Make sure you have positive drainage. At the end of the tile install a NDS pop up emitter. You can get this at most box change hardware stores. We install these up in the St.Paul/Minneapolis area and do not have problems with winter freeze up. They work very good. You can use the excess soil from digging the new trench to replace the washed out area behind your existing boulder wall. Apply a heavy wolven fabric between the boulders and dirt, this will stop future wash out. You are going to have to get the water away from the walls or this problem will never end. You may need some more drain tile and a few connectors as well. Its going to be a little bit of work but it will fix the problem.
 
  #4  
Old 01-22-08, 02:00 PM
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Join Date: Oct 2006
Location: Madison Wisconsin
Posts: 68
Clecker on boulder retaining wall

Hey Clecker,
Thanks for your response. I do have some questions however.

1) Do you mean reroute the drain tile/downspout to come out "between" the upper and lower sets of timber steps? Why is that the best spot for re-routing?

2) Why do I need a NDS emitter? What function does it serve?

3) Between boulders do I apply heavy woven fabric and then top with soil?

I moved to Madison from Edina last year and will be up in Mpls this week-end for a visit. Great town!! Thanks so much for your help with this.


Regards,
wvdthree
 
  #5  
Old 01-22-08, 03:28 PM
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Join Date: Jan 2008
Posts: 5
1. By the photo you posted I was taking a guess that the grade between the two walls angles down as it goes towards the street. (maybe it dosnt). If it angles towards the street as you install the new tile it will give you positive drainage. Run tile towards street. May have to add some footage.

2. The NDS emitter is about 6" round and green the water pressure from your downspout will open a valve to release the water. When it is done the valve closes. It looks like a round irrigaton box. We install alot of them and dont have any problems.

3. The fabric goes behind the boulders to keep the dirt from washing. boulders, fabrc, fill. Compact the fill as you go so you reduce settling. Stomp you foot on it.



Chad
 
  #6  
Old 06-10-08, 09:02 PM
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Join Date: Jun 2008
Posts: 1
Pop Up Emitter

Originally Posted by cklecker View Post
Here is what I would do if someone called my company. I would re-route the tile so it goes between the timber steps. Make sure you have positive drainage. At the end of the tile install a NDS pop up emitter. You can get this at most box change hardware stores. We install these up in the St.Paul/Minneapolis area and do not have problems with winter freeze up. They work very good. You can use the excess soil from digging the new trench to replace the washed out area behind your existing boulder wall. Apply a heavy wolven fabric between the boulders and dirt, this will stop future wash out. You are going to have to get the water away from the walls or this problem will never end. You may need some more drain tile and a few connectors as well. Its going to be a little bit of work but it will fix the problem.

Hi. I'm new to this site, but wondering if I could ask you a question regarding the pop up emitter. We recently had a sump pump hose, buried under sod without putting a pop up emitter. Can you tell me if this will cause a problem?
 
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