Question about a small retaining wall

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  #1  
Old 06-12-17, 01:31 PM
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Question about a small retaining wall

I'm looking to build a low retaining wall, one that ranges from three 4x4's in one small area, down to a single 4x4. It's mainly there to keep soil in on a sloped bed adjoining a brick path. Here's the basic layout:
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The dark line at top is an existing 6x6 wall. Section A, the 16.25" section leading off that 6x6 wall, will be three 4x4s. Sections B and C will be two 4x4s high; Section D will be a single 4x4.

Everything above the dark grey line is dirt. Everything below it is brick.

I'm planning on staggering the joints, so for the corner where A and B meet, A will go that full 16.25" length, with B butted up on its right side, and on top of that, B will sit on top of A, with a shorter length of A butted up against it at top. The third section of A will be cut at a 45 at the end, but sit on top of that end of B. Similar thing at the joint of B and C.

My questions:
-- my first thought had been to put several vertical lengths of 4x4 into the ground behind the wall, to hold the wall in place. Second thought was to drill holes through the 4x4s and hammer rebar in. Which one would be best, or do some combination of both? I'm not imagining there's be great pressure behind this wall, considering how low it mainly is.
-- how should I join the different lengths? I have the three corners (A to B, B to C, C to D), and section B is long enough that I'll need two lengths of 8' 4x4 butted together. And at two of the corners the height drops from 3 pieces to 2, then from 2 to 1, so I won't have anything to attach that top piece to except to the piece below. Unless I toe in any screws, I'll need pretty long fasteners to make it through a 4x4 and still bite.
A couple of Home Depot employees suggested using things like these but I'm not sure I'm wild about the idea (or the look).
 
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  #2  
Old 06-12-17, 03:58 PM
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Would you be able to post some pics of the actual location? I have a feeling that I'm not the only person who is having a problem following your diagram.
 
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Old 06-12-17, 04:47 PM
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OK. In the image below, the thick black horizontal line in my drawing is the 6x6 in the left of the picture, running approximately up and down. The two short pieces of stacked 4x4 towards the bottom will be the segment I labeled "A" in my drawing (they're just there as reference for the picture).

Running away and to the left from those 4x4 pieces is section B, ending a little past that sprinkler riser, with section C then running to the right, past that patch of prickly pear cactus. Section D will run at a right angle to that.

All of these sections will be positioned on the dirt right where the brick ends; it's hard to see the demarcation in the picture, but that's why I'm putting the 4x4s in--the dirt spills over onto the brick.

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  #4  
Old 06-12-17, 05:36 PM
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A retaining wall usually starts below grade. That's how it gets it's strength. The strength of the structure in your design would depend on the brackets between the lengths of 4x4s & the 2 or 3 vertical 4x4s that you mentioned. How well that might work depends on the weather, in your location.
 
  #5  
Old 06-12-17, 06:23 PM
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Well, I'm going to do a little digging, probably bury about the bottom third or so of the 4x4. Doesn't sound like a lot, but that means it's pressing up against the brick, for added strength. But there isn't going to be a lot of weight against the back.
 
  #6  
Old 06-13-17, 12:27 PM
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Here's what it's looking like now, the wood cut to fit but not attached anywhere. Everything's levels and pretty much fitted, though I might dig the trench a little more. It's hard to see but the bottom is about 1-1.5" below the level of the brick.

I happen to have a bunch of these, which i was going to use at the corners (vertically), where I have the different pieces overlapping. That'll hold them together pretty well, I think.

I'm not sure about the two end-to-end butts, though (section B, which is longer than any 1 piece of 8' 4x4). I'll either need a sort of plate, or put vertical pieces of 4x4 at the junctions and screw the ends of each piece into it. Not sure if there's enough overlap there. The vertical 4x4 would also go into the ground.

For added stability, how far into the ground should the vertical 4x4s go?

I also got 2' pieces of coated rebar, thinking I could cut 1/2" holes at intervals and pound the rebar through, into the ground. Overkill?

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Old 06-13-17, 04:06 PM
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That looks good. The depth of vertical posts usually depends on the frost line, if you have a frost line. If there is none, 2 feet are sufficient. Any L shaped bracket should work on the end butts. I would use a Strong Tie marked Z. Somewhere along the line the chemical in pressure treated wood was changed & had a chemical reaction with the metal. That's why the Z is needed.
 
  #8  
Old 06-16-17, 11:50 AM
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OK, I went with rebar. 2' hammered through 1/2" holes drilled in the wood, one piece of rebar on section A, three each for B and D, and two for C. Corner brackets for where sections A and B, and C and D are attached, straight braces where B and C attached. I initially made the mistake of getting two corner brackets for B to C, thinking it as an outside corner (to the inside corners of A/B and C/D) but it's not actually a corner, not where the pieces are joined--the side of one piece is flush to the end of the other, so it needed a straight brace. More straight braces to attach the short pieces that make up the rest of section B. So, here:

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Thanks for the feedback.
 
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Old 06-16-17, 02:25 PM
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It should be fine.
______________
 
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Old 06-19-17, 06:33 PM
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Thanks for all the feedback.
 
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