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How to build a long lasting, healthy, narrow retaining wall

 
Mike Jay
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Location: Northern WI (zone 4)
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Hello permieneers! I am building a lean-to roof off the side of my barn and need to create some flat space. I'm digging into the slope next to the barn and need to hold back that dirt (see photo). It will be about 4' high at the barn, 2' high at the other end and about 16' long.

Challenges:
I want to build this with a low environmental impact and low cost.
I'm in a medium-wet climate so buried logs won't last long
I don't want to lose a bunch of future floor space to a gabion cage style wall
I have a foundation repair anchor supporting the barn wall buried in that lump of dirt so I can't dig back more than a foot or so from the future wall position (IE no dead man anchors)
I'd rather not spend $450 on a bunch of retaining wall blocks

Advantages:
My labor is abundant and affordable
The soil is very sandy so I believe it drains well
There is an old footing that extends from the barn across the width of the retaining wall. Problem is that it's 3' inboard of where I want the wall. If it was only 3' farther back...

Past history:
The backside of the footing was poured up against round logs as a retaining wall. They rotted, the wall failed and the footer disappeared for two decades until we uncovered it.
It isn't square to the barn but I'm ok with the wall not being square. I guess... Who makes a retaining wall 1.5' out of square in 16'? Sheesh....

Current plan:
I think I'll dig out behind the footing 8" deep and lay down some extra cinder blocks I have flat side up. They'll act as a 32" wide cement floor. Then next to those I'll put a row of cinder blocks holey side up as the base of the wall. Then I'll stand 2x4 oak pallet runners into the holes as vertical wall members. I'll have gravel in the cinder block holes to keep the bottom of those runners from staying in contact with damp soil. At this point the "wall" will be a picket fence of oak 2x4s with the bottoms supported back to the footer by the cinder blocks.
I'll put visqueen plastic on the uphill side of the 2x4s to keep dirt from rotting them out. I can tie them together with more oak runners or a 2x12 that runs the length of the top of the wall.
The basic problem that I see is that the bottom of my wall will be kept from kicking out by the footer and blocks. But the top won't have much resistance to tipping.

Are there other ways to do this given my situation? I see wofati walls that appear to be vertical round logs but I'm assuming there is some way that they avoid tipping? And I'm assuming that in a wetter area they would just rot after a decade or less. Maybe I'm wrong though?

Thanks for any help or ideas!!!

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Wall location, footer barely visible
 
Glenn Herbert
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Location: Upstate NY, zone 5
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At first I thought you were trying to make the floor of your lean-to space built up with the retaining wall, but the picture looks like you are just trying to hold back the bank from your lean-to floor, right?

One of the main principles of dry-laid masonry walls, especially retaining walls, is that the face slopes back ("batters") about one in six. As long as you have a good solid base for your wall, you can have a fairly significant batter and the earth behind it will stay in place. Essentially, you are using gravity to make the wall lean on the retained earth. If you were using stone or block for the whole wall, you would lay them so their tops were not horizontal but drained back to the inside. The significant part of this for your situation is that you don't need a thick base as long as it is solid; the wall can lean back and be fine. If the soil is sandy and well-drained, you may not have to worry about frost heave so much. I might batter your lightweight wall severely, like a whole foot at the high end and six inches at the low end. The more heavy material you can use for the retaining wall, the better this principle will work.
 
Mike Jay
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Location: Northern WI (zone 4)
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Yes, I am trying to hold back the hill so it doesn't slump down into the lean to floor space.

Thanks for the batter information, I hadn't heard about that before. I know the little retaining blocks I've used before have lips at the back that force a batter. I thought it was just to lock the wall together. Now I see it is also to fight the dirt pressure.

If I were to build the wall out of oak 2x4s and angle them back a foot at the high end of the wall do you think it would have enough weight to keep the dirt from pushing the wall upright and then over?

Thanks Glenn!
 
Glenn Herbert
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That wouldn't have enough weight by itself to be stable against soil pressure. It would depend on anchoring at top and bottom (the 2x12 you mention being tied to the barn wall at the high end perhaps), but the batter would still reduce the pressure and give it longer before the geometry starts to be actively unstable. Do you have any stone available?
 
Mike Jay
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That's what I suspected... I was toying with the 2x12 attached to the barn at the high side and braced off of the footing at the low side.

Unfortunately I don't have any heavy block or rock around. I have seen some very small piles of round field stones in the area but nothing bigger than a volleyball. And I haven't seen enough to do even 1/10th of the wall.

If I went to the scrapyard and found some beefy aluminum or steel posts, could I post hole down a couple feet and set them as retaining wall supports? Maybe by having them 2' underground it would give the support to keep the wall from tipping? Especially since they'd be braced at the floor of the lean-to by the footing? Here's a crude side view:
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John Weiland
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Had to delete this last night due to lack of time to complete the entry. You could also try something like the photos below if you are able to excavate far enough back into the bank. I'm not an engineer and am not recommending the materials that I used, but the general concept of an outlay may be of use. The soil I'm holding back which is heavy clay is not as tall as yours, so that should be taken into account. I can elaborate more if interested...
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SoilBerm2.JPG
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Glenn Herbert
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That looks like a very good plan. The existence of the old footing is crucial, as the big issue with such a retaining wall would normally be the posts tipping in the ground. I think I would give this design a bit of batter, partly because it is likely to move a tiny bit just from all the parts settling into place. If it starts perfectly plumb, every bit of movement is bad.
 
Mike Jay
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Location: Northern WI (zone 4)
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Thanks for the photos John but I can't dig back into the hill because there is another anchor there that is "repairing" the bowing block wall on the barn. The wall is stable now but I can't dig within 4' of that anchor so "deadmen" braces won't work for me

Thanks Glenn! After all our talk of barter I forgot to include it in the sketch Cool, so I'll see if I can find some beefy metal posts from the scrap yard, install them with some barter, put my oak cross boards in, put visqueen on the dirty side to keep the oak from rotting and include a bit of drainage. Woo hoo, we're off to the races....

And for those of you reading this in the future, I agree that this plan wouldn't work without the footing there to support the posts at the ground level of the lean-to. Although maybe it would if the posts went deep enough into the ground...

If I remember, I'll post photos when I'm done.
 
Mike Jay
Posts: 244
Location: Northern WI (zone 4)
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food preservation hunting woodworking
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Ok, here's the update!!!  

I generally stayed with the design as laid out above.  The main differences are that I got some extremely burly pallets (6' by 3') to use as the wall.  I also took some apart to reclaim the main runners of the pallets which are 4x4 oak.  They became the posts that go down into the ground and are braced with the cinder blocks.  Each pallet weighs about 150 lbs!  So then the issue was protecting the posts from rot.

Enter the "SmartPost".  I saw these advertised in Acres magazine.  No website but when I called they sent me the info.  1-888-519-5746 or smartpost.postsaverusa@gmail.com  It's a 3' long heavy duty plastic boot/sleeve that you put the post into.  It would easily handle a 4x6 post.  They say the wood in the boot lasts longer than the wood exposed to the elements above ground.  By using those I figure I can use the oak posts underground to hold up my wall.

So I excavated the hill which was easy due to the sand.  In the process I uncovered years of old junk (lightbulbs, gas fittings, barbed wire, etc).  Then I laid out the cinderblocks so they would push against the existing footing.  Once I knew where they ended, I dug the holes for the posts at an angle.  I put the posts in and packed the post holes full.  I put the pallets behind the posts and elevated them off the cinder blocks a few inches.  Visqueen plastic went behind the pallets and drain tile went behind that.  Hopefully the pictures do it justice and remember that the footing was 1.5' off of square to the building so I adjusted for that with different amounts of cinderblocks.
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Cinder blocks laid against old footing
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Sleeve on post
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Post in ground
 
Mike Jay
Posts: 244
Location: Northern WI (zone 4)
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food preservation hunting woodworking
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More pics...
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Posts in
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Pallets attached with plastic behind
 
Glenn Herbert
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Location: Upstate NY, zone 5
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Nicely done, Mike!
 
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