So I played around with calcs for a timber retaining wall with deadmen... 2

[PropertyGuy67]

I have a client who had a contractor install a timber retaining wall for an area that will end up having a very large surcharge load, and to his credit, he had second thoughts and called me. Right off the bat I could see it was wonky. The wall was placed on a 45 degree slope, zero coverage at the toe, and you can stick your hand under the bottom timber in several areas. And there were only two deadmen along the entire wall. I advised the owner that timber was going to rot away eventually, and to do it over properly with either SRW or gabion cages (or place a new wall out in front of the timber if he didn't want to dig up what was already installed). Owner subsequently called his contractor, who in turn requested to see my calculations. I got paid for it, so I did it. I gave him my sliding stability check, using a calculated tie-back resistance force from the face of the deadmen, based on what the contractor said he installed. Of course it failed miserably, mostly because there is no resistance at the toe. What was interesting is that as long as you avoid a surcharge load, keep the toe buried, and install enough deadmen out beyond the slip plane, a timber wall with enough deadmen actually calculates out properly. But doing all of that with a material that will rot away in 10 to 20 years is ill-advised.

 

[BigH]

I think that one of the first questions would be: How high is the wall? The second question is to provide a picture or a sketch showing the cross section and how the wall sits on the slope. A third question is what is the nature of the surcharge loading and finally what is to the outside of the wall - and what effect a large distress might have. It seems strange that the owner has qualms and yet isn't receptive to act on those qualms.

Timber crib walls have been used for a long time; usually they are creosoted or provided with other preserving chemicals to prevent rotting. This is especially needed, in my view, for walls that will undergo wet and dry cycles. Timber piles below the ground water level will last a long long time (Swedish Parliament Building built in 900 AD (if I remember right) are on wood piles.

The fact that the wall is not placed on a footing or embedded into the ground is of concern of course.

https://www.pwcgov.org/government/dept/development/bd/documents/002004.pdf

https://www.fs.fed.us/t-d/pubs/htmlpubs/htm04232825/page33.htm

 

[John2025]

BigH,
The trail building guide is great. I've been involved in mountain bike and hiking trail building and the guide makes for great reading.
Thanks.