Natural Boulder retaining walls

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Old 01-10-13, 10:46 AM
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Natural Boulder retaining walls

Does anyone have any experience with building natural boulder retaining walls? I've read a bunch about them and just wanted to get the thoughts of some people here. This wouldnt be a true DIY project, more of a design it myself. My lot sits in the middle ground of two hills (smallish hills, on about 4ft high and the other maybe 6ft high). A local quarry (SE PA) sells their boulders for $60/ton with 4-5 boulders equaling a ton. I love the natural look of the boulders (they're cut with flat sides, so made for stacking, etc) and feel they'd be aesthetically and economically appealing. I have read that the normal water run-off measures are unnecessary with walls of this type since water can seep thru the spaces between the rocks (would still have it built on a 6"-8" layer of stone and backfilled with stone) and was wondering if this is true and if there are any other issues to be aware of regarding a wall such as this. Thanks in advance.
 
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Old 01-10-13, 11:08 AM
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I have one dry stack retaining wall made of 2 ton concrete blocks 10 feet high and stacked on virgin earth with no drainage other than what occurs between the blocks. Still, almost 11 years old and with no foundation it's still straight with no sign of movement. I also have numerous dry stack natural field stone & boulder walls of varying ages and they also hold up incredibly well and with no maintenance.

Any failures are all related to the stone I use. It's all from my property and neighboring fields and of varying quality. Some of the poorer quality stones crack after several winters but the walls still stand and look great.

There's a reason walls like that can last for thousands of years. It just works. Stone & gravity. Not much to go wrong if done somewhat properly.
 
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Old 01-10-13, 01:21 PM
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Dane,
Thanks for the response. What you said is what I figured to be true. It's one thing for the earth to heave a bunch of 20lb concrete retaining wall blocks, its entirely different to heave a bunch (or any) large natural boulders.

One additional question, do you live in a "permit-intensive" area and if so, did you seek out permits for your walls? If you did, how much push-back did you receive to not installing the type of drainage that a block retaining wall would require?

Chris
 

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Old 01-10-13, 04:04 PM
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Just wanted to throw in here....

Many homes in this area are built on giant piles of dirt (20-50+')..then a big loader crawls up there and stacks boulders all around the mound. AFAIK...I never saw any fabric or screens of any sort put in. I'm guessing they may have some sort or drainage system...but I never saw it during construction.
 
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Old 01-10-13, 04:20 PM
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Gun,
Thanks for the reply/input. It's further in line with what I was hoping. Simplicity. I figured pouring and tamping stone in behind the wall would help act as a filter to let water pass but keep most of the mud away from the wall.

PS-love the screen name
 
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Old 01-10-13, 07:31 PM
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Unless you live in a very arid region, tamped stone (typically) will not keep mud from wanting to run out from between the boulders. In areas of moderate to heavy precipitation, using native soil for backfill, you can expect to get some mud flow. Easily avoided by spending a few bucks on a roll or two of filter fabric, laying it up against the back face of the boulders while backfilling. If more than one horizontal run of fabric is used, overlap previous runs by several inches (placing higher runs on the outside of previous ones). Fabric will also minimize the likelihood of weeds growing through the joints between boulders.
 
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Old 01-10-13, 08:09 PM
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I did a large boulder wall project last summer and I am rather happy with it. Total was 69 tons delivered in 3 loads. Boulders vary from 36" - 18". These could not be moved by hand, and required the use of a 30HP tractor with a grapple. Behind the boulders, I used 8oz fabric which is kind of like a heavy felt to let water through, but keep the soil back. If you do not use a fabric the soil behind the rock will erode through.

Go here for a picture of my wall: http://www.doityourself.com/forum/br...-wash-out.html

My wall is in one of my posts.
 
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Old 01-10-13, 08:28 PM
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Thanks, guys. I don't live in a dry area, so I'll be sure to use fabric.

Tolyn, if you don't mind me asking, could you give me an approximate range of what your project cost was (not counting any finishings such as sod/plants/patio etc)? $10k? $15k?
 
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Old 01-10-13, 08:34 PM
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also, nice work, Tolyn.

and another question: did you lay your first course on the native soil like Dane mentioned or did you dig a trench and fill with tamped stone for a base?
 
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Old 01-11-13, 06:56 AM
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In my area a permit was not required because I was far enough away from the house. They determined that by going from the lowest corner of the house's footings and draw a 45 degree cone down. If the wall was outside that no permit was required at the time (11 years ago). Even with the height of my retaining wall no railing was required at the time since it was considered landscaping or ornamental and not in the scope of the codes at the time.
 
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