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Assistance With Retaining Wall, Wood vs. Block?

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I stumbled across the seaint site while researching wood retaining walls. I am not an engineer but judging from the archives this looks like a great place to ask for some engineering suggestions. I am a computer geek by trade with a background in home construction and remodeling.

The issue is that I need to build a retaining wall that is approximately 80 feet long by 7 feet high. The wall is in my back yard, is typical Northern California clay/silt sort of stuff and has no load above.

The foot of the wall will sit on a graded area that extends out to a slough (a one ended river in the Sacramento River delta). The seawall is a CMI wall ( and is about 20 feet from where the retaining wall will sit. The retaining wall will not sit in water but the water is not far away (I assume this is significant). Water will occasionally flood the area during a very high tide but it is not long lasting. The area may be wet but not what I would call standing water.

I have looked into the systems such as Keystone. Keystone or equivalent appears to be an excellent solution and they provide enough engineering detail that anyone reasonably competent should be able to build a wall such as I need. It's pretty expensive though, around $10,000 for material alone.

I got to thinking about how far the technology for treated wood products has progressed. I can get the materials for about half the cost if I do something like 8x8 posts on 48in. centers with 2x10 planks across. The labor cost will be significantly lower also. The real problem is there is not much engineering information readily available.

I ran across some info that suggested the wood posts should be buried the same distance as the height. I can't begin to imaging how I can dig a 7 foot deep post hole. The use of a deadman system is frequently mentioned but no useful details for layout.

I will appreciate any comments, opinions or suggestions. I have a gut feeling that wood is not the way to go structurally, the interlocking block solution is just so darn expensive.

Rick Reineman

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