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dry stack retaining wall  RSS feed

 
steward
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Location: missoula, montana (zone 4)
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I thought it would be good to have a place to collect pictures of everybody's dry stack retaining wall projects.  Mostly because I just came in from doing some.

Due to some health comedy, Jocelyn and I attempt to go outside twice a day and work on something for 20 minutes.  I think that this is day five for this project.  One more day to be done. 

In the first pic, you can see how this is trail from the turtle lot up to the fisher price house.  You can see some of the turtle art (thanks bill!)

The second and third pic are the same, but the second pic has me drawing on it.   I am attempting to show what Emily and Tony built about four years ago (lower right).  We added all the rocks to the left of that.   I've added a bunch of dirt on top of the trail for Emily and Tony's wall.   And I have raised the trail a bit up to where I wrote "done".

Past "done" we need to add some more rocks and then add dirt on the top for the trail to be above the rocks. 
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Location: Arkansas Ozarks zone 7 alluvial,black,deep loam/clay with few rocks, wonderful creek bottom!
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These are our old homestead garden dry stack terraces/retaining walls that Steve built back in the seventies over a period of several years.  They will last forever although his back did not.

Beautiful and long lasting as these terraces are all I can think about when I look at them now is the back surgery he is having in june...lumbar fusion complete with metal parts and bone grafts....due to this and all of the other hard work he did over the past forty years.



 
pollinator
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I love rock walls, but then I live in New England too.

This I my back patio area with a gas grill tucked into a rock wall, and then a granite seat.

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Travis Johnson
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I used a lot of dry laid rock for a couple of issues I was having in an area of my farm on a project last summer.

Here I installed (3) rock check dams to prevent erosion, though only 2 are in the view of this photo. The other problem I had was, I needed a way to cross the swale with my tractor. So I used dry laid rock to build a Ford across the area.

How did it work? GREAT!!

This winter I had a culvert freeze up, and the result of that sent water from two swales down into a second swale that was not designed for it. It ran through here, but the rock dams held erosion at at bay. I even was able to cross this Ford in the middle of mud season with my tractor, so it worked as planned.


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paul wheaton
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Done!

Woman for scale (hi jocelyn!)

We added several inches of dirt to the trail which will, in time, pack down.   The trail is now much wider. 
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stone was dug from property. roundish stones
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Erik Rowberg
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not retaining wall but garden wall.  used some clay mortar
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paul wheaton
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Here is something that can make a big difference when considering a dry stack retaining wall - starting at about 3:30



I know that when building steep hugelkultur, it is important to have sticks going every which way for this reason.  We had a permaculture instructor here that was really upset about our berms and hugelkultur beds because they were steeper than "the angle of repose."  But I think having the wood criss-crossing all over on the inside helps with that dramatically.

Further, when it comes to retaining walls holding back a rather sandy material, usually the dry stack ends up super thick on the bottom.  BUT - it does seem that if a person uses some of this technique, they might be able to lay down some meshy material horizontally within the sandy material and, thus, build something behind the rocks that won't be perfectly stable, but it will be MORE stable.

 
paul wheaton
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In this video, the guy is putting HUGE work into the retaining wall:



From watching heaps of other videos, reading articles and books over the years, there are two things I see here that I would want to suggest:

   - make the wall indent in ... lean in .... not so much a vertical wall

   - when filling in behind the wall, use a lot of bigger chunks of sharp rock.  Definitely not rounded rock.

 
paul wheaton
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this video has a lot of good info:



Good stuff about:

   - make the wall lean in

   - set your rocks so the length of the rock goes into the middle of the wall rather than along the wall (3:33)

   - don't have running joints (4:05)

   - starting the build on top of the soil rather than starting below the soil.  That can be okay.

   - tie stones and cap stones


"the difference between a waller and a mason is that a mason will shape the stone before putting it in the wall."

I like how he is saying that it is better to lay the stone correctly than to add cement.  And it shows how the wall failed even though cement was used.

Something I would like to add is that this guy is talking about how you make a good stone retaining wall that can last 100 to 1000 years.  I would like to hear him talk about a recipe where you can build the wall 20 times faster and get a wall that will last 10 to 40 years.  I think that the retaining wall that jocelyn and I built went up about 20 times faster, but is not going to make it to 100 years. 

For example, he says "keep courses level" (4:19).  I think you are now getting into that space where you are making a wall to last more than a hundred years at the cost of shaping the stone for each course rather than stacking what you have. 

 
gardener
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The common rule of thumb is to make a batter of about 1" per 6" of height.

Also, sloping the horizontal surfaces a bit back into the earth instead of making them dead level will improve the strength and durability of a retaining wall.

The gravel in the video, even if it is crushed and not round, will tend to flow and put more stress on the wall. Larger flat or angular rocks would definitely help (though the stones shown are massive enough to not need help).
 
Glenn Herbert
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I expect practices vary depending on the character of local stone. A lot of northeastern stone walls have a preponderance of flattish rectilinear stone which makes coursing easy. Some places (like New Hampshire) have nothing but rounded granite boulders, and they have to either use extreme batter or split all the stones to get angular pieces. Other places, like Wheaton Labs, appear to have mostly irregular angular stone, which can be fitted to be very strong with skill and time. The best Inca walls are all irregular fitted stones, and have survived 500 years of earthquakes without damage. Not having continuous planes of coursing is a large part of that.


I think the retaining wall you and Jocelyn built could have been made to last 100 years by giving it significant batter, like 1 in 4. That way, the stones are decidedly always falling back into the hill, and unless the base gives way, will be very stable. There is a drainage ditch causeway on my property, at the head of a small ravine, where the farmer just threw irregular stones in until the top was level with the fields, with a slope of 1 to 1 or flatter, which still drains runoff and storm water through the crevices and is sound after more than a century.
 
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paul wheaton wrote:this video has a lot of good info:



Good stuff about:

   - make the wall lean in

   - set your rocks so the length of the rock goes into the middle of the wall rather than along the wall (3:33)

   - don't have running joints (4:05)

   - starting the build on top of the soil rather than starting below the soil.  That can be okay.

   - tie stones and cap stones



This bloke really knows what he's talking about, great video!

Having done a bit of dry stone walling, I can say that while it's easy to understand the basic principles it can be quite difficult to put them into practice. Especially if your stone happens to be of the awkward variety! I've always been told that the occasional deliberate mistake can be acceptible if there are no other options. You'll see in the video that there are some running joints but not too many. There are things you can do to mitigate some tracing or running joints.

For tracing, and as a general good practice for walling, you're trying to trap the stone with as much friction as possible. If the traced stone is firmly gripped by the stones next to, beneath and above it, then this is good. I would ensure that these stones were laid into the wall as it's important not to have another or multiple traced stones in the same location as this just compounds the weakness in that section.

For running joints I have been told that two stacked stones is fine but three is not. Again, you want to ensure that the neighbouring stones are well placed in order to mitigate any weakness from the running joint.

Another consideration is 'bridging'; this can happen when your coursing is uneven or if you're using smaller/larger than ideal stones. The stones you lay want to be sitting "two over one and one over two" much like in bricklaying so, if you end up doing one over three, you are bridging the middle stone and thereby establishing a weakness where the middle stone is not being trapped and held by the stones above it.

In terms of a walls foundations, I have always been told to dig them in unless we've been building on bedrock. If not, soil can be erroded from beneath the wall by wind and water allowing the bottom course of the wall to shift over time.

If your tie (or through) stones aren't long enough you can get at least some of the benefit by having the longest stones you can find sitting at least half way but ideally 2/3 to 3/4 of the way through and then alternating the side in which the end of the tie stone is hidden in the wall. As the stone that makes up the final 1/3 or 1/4 will be at a relatively shallow depth it's important that it is trapped by a longer stone or stones above it.
 
Travis Johnson
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Here, you can walk around and look at all the rock walls that were build (most between 1830 and 1850), and see why they hold their shape, or why they don't. Where the rock walls sit directly on ledge (bedrock) they hold their shape because frost does not knock the rock wall around.

Frost is a killer on a rock wall.

It moves 9-11% by volume, and it does not matter if there is a 1 ton rock wall above it, or a 250 ton house; once the ground gets below 32 degrees, the water freezes and expands.

I have built a lot of rock walls, and this time of year (Spring), I will walk around before the grass gets high, or the snakes come out (I really HATE snakes), and see where the frost has played havoc with a rock wall, redo that section of the wall, and then keep going. It is just a yearly type of thing.
 
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Seeing the title on the Permies topics you might have missed note, my immediate thought was drystacked concrete block, which I have studied a bit.  But, since it isn't I'll forgo that.

I have a deck to rebuild at some point, and the issue of how deep and frost always comes up for me (I live at 56N).  There are places in the southern continental USA that seldom get freezing.  Go further north, and you might hear about a frost line.  By the time you get to Minnesota, people are talking about a 4 foot frost line.  Climate has changed since I was in high school (late 1970's), but at one time projects like pipelines had to assume the frost line was 9 (nine) feet down.  The people building decks and similar things, are typically required by building code to put a foundation below the frost line, whatever it may be.  But in just about every situation, you may not have to go for to fine a farmer who has fence posts in the ground, which are typically stable (exceptions exist), and they are nowhere near the frost line with no foundation at the bottom of the hole.  Mind you, unless you are a squirrel, you probably aren't living on a fence post.

What seems to be happening, is that the building code almost everywhere, is assuming worst case soils.  And if you want to see what frost heaving can do, there are some natural "hills" near the arctic coast which are rather impressive, all built by the action of frost on a susceptible soil.

If you have a water table above the frost line, water will freeze in the soil.

For all other circumstances, one has to consider the soil.  If the soil is sand(y), water readily flows through the soil and goes to depths below the frost line.  What is left behind is sand and air, and heat transfer is lousy from the surface to below.  Lousy heat transfer and no water to freeze - no heaving.  If the soil is clay, the clay could be dry or wet.  Many clays change volume on absorbing water (swelling).  But by and large, water cannot flow through clay.  Clays also tend to pack well, and so the void fraction tends to be low, and the soil doesn't actually contain a lot of water per unit volume.  Heat transfer can be quite good if the clay is wet.  So there is a slight problem with frost heaving of clay type soils.  Where the problem seems to lie, is in the silty region of soils.  Large pore volumes, good heat transfer and reasonable water transport.  You can get a freezing event (expanding the pore volume with frozen water), the jagged silt particles temporarily maintain structure, melting happens and new water enters the soil, and on the next freezing event we get more freezing, lifting things more.

Where I live, most of the soils are either sand or clay based.  Neither one being strongly affected by frost heaving.  Fence lines are stable to frost heave, but we get enough wind that the wind can push fence posts sideways over the years, especially with board fences.

If you are worried about frost heaving issues, having someone examine the soil to see if it is susceptible is probably a good thing.
 
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