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Old 09-17-2017, 04:58 AM  
soparklion11
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Default Landscape Block Wall

I'm planning a small landscape wall to alter the drainage around my house. It will be ~3 ft tall tapering to 2 ft over a span of 11 ft before ending.

I plan to use the stone pictured in the attachment.

How many inches do I need to excavate behind the wall? I plan to back-fill with large gravel (#57 stone). If I use #57 stone, do I really need a drain pipe as well? I plan to protect the backfill with landscaping cloth.

In your opinion, is it worthwhile to fill the voids in the block with gravel? Will it make the wall more sturdy?

Thank you!


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Old 09-17-2017, 07:44 AM  
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Garden walls higher than 2'6" are considered to be retaining and should have an appropriate footing, rebar and grout, as well as the appropriate hydrology drain.

Generally the french drain is placed behind the first coarse, encased in gravel and the excavated slope backfilled.

What is the slope of the excavation? 1:1 is a 45 degree.


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Old 09-17-2017, 09:28 PM  
slownsteady
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That may be California rules only, but it pays to check for any local code.
You only need to have enough room behind the wall to work comfortably, but you should go low enough to put in a good solidly tamped down gravel bed. If your objective is to alter the drainage, don't cheap out by skipping the french drain. Bury the fr. drain and the first course and back fill with gravel as you go up. I'm not familiar with #57 stone, but you don't want to have large voids between the stones...they will fill with something on their own. You don't have to fill the voids in the block, just factor in a top row of cap stones which can be glued down with landscape adhesive. Anyways, that's how I would do it; local conditions may influence how you make it happen.
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Old 09-17-2017, 09:32 PM  
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Hydrology affects all retaining walls.

Fail to address it at your own peril.
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Old 09-17-2017, 09:39 PM  
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I like allan blocks more because the lip on the front helps getting th slope back angle right.
I think you can go 36" with them before you need an engineer.
https://www.google.ca/search?q=allan...w=1682&bih=835
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Old 09-18-2017, 02:33 PM  
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Soparklion11 -

That unit you show is really not a good unit for a retaining wall unless there some secret hidden in or behind what is seen.

When you lay a conventional shape block like that on top of another, the block can just slide with any soil pressure below and any soil crumbs act just like oil to lubricate the surfaces. - Rock in the cores will help a little, but it still cannot be considered a "retaining wall unit" by any stretch of imagination. - You need some sort of key or projection to maintain stability.

The Allan Block is one and I have also seen others that had a "lip" or key on the lower back of the block and served the same purpose.

There are many other units (the good licensed products and even the "knock-offs) will work for your situation, but a lot of the "knock-offs" lack some features. - Stick with the good units.

Most codes to require some sort of engineering for retaining walls over 4', but then you get into soil reinforcement (geo-grid, etc.).

In my 40 years experience in the block business, I made most of the major block used for testing and approval purposes plus a few other types that never succeeded.

Dick



Last edited by mudmixer; 09-18-2017 at 02:36 PM.
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