Best underlayment for short retaining wall.

I'm putting in a 2 course retaining wall around some shrubs in raised beds in the front yard where previously there were landscape timbers. Since I was only going up 2 courses (8") I just figured to dig down a couple of inches and lay down some sand to make leveling easier. But, then I was thinking that maybe pea gravel or crushed limestone would be better or maybe I should go deeper. What do you guys think? By-the-way this is in zone 5 (Michigan).
Thanks, Craig
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I am pretty sure you need to have at least 1/2 of a block below grade to promote stickiness of the wall.
I would use at lest 4" of compacted, crushed stone under the first level of blocks. Then use 1/4 -1" max of rock dust or sand for the final leveling.
I am building one as soon as I can find the time in my own yard. The height will vary from 2-6 blocks and I will put a 1 foot wide base 6-8" thick over compacted clay. With a lighter soil I would use more base especially under the taller part. My always stay where I put them.
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Are you talking about the interlocking concrete retaining wall block? If so, you don't need gravel or crushed limestone under such a minimal 'retaining' wall. It's really more of planting bed edging. Even if the ground freezes up, the whole thing, planting bed and all, will rise and fall with the drop in temperature below freezing. There's not enough of a structure to be disturbed by such an ebb and flow. Fear not.
R
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wrote:

Are you talking about the interlocking concrete retaining wall block? If so, you don't need gravel or crushed limestone under such a minimal 'retaining' wall. It's really more of planting bed edging. Even if the ground freezes up, the whole thing, planting bed and all, will rise and fall with the drop in temperature below freezing. There's not enough of a structure to be disturbed by such an ebb and flow. Fear not.
R
Thanks, I've built paver patios and wasn't really looking forward to digging up all that dirt for limestone+sand. I just didn't want to be out there in the spring redoing it all.
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