treated wood retaining wall

I have an 18 year old treated wood retaining wall that is failing. Can I leave it in place and construct an interlocking stone wall in front of the existing wall, in essence burying the wood wall behind the new stone wall? I have an exstensive garden above the wall, and removing the "dead men" from the existing wall would be a major undertaking, as there are mature trees and shrubs, perennials, etc. that would have to be contended with. The wall is roughly 3 feet tall and about 130 feet long with 2 "bump outs" in the shape of a half hexagon that the original contractor added so it was more interesting visually, not just one long wall from one side of the yard to the other. I can leave some space between the two walls and fill the void with gravel to improve drainage between the two walls. The wood wall is infested with carpenter ants and it is just a matter of time until it will force us to deal with it. If I can put the new wall in front of the old, then if the wood wall collapses into the dirt, I would still have the new wall to retain the earth. Can this be done?

I would think you could do that--just make sure that the stone wall is designed correctly to hold back all the soil when the wood eventually does all rot away.

Good news and bad news.

A 3 foot tall retaining wall of any kind is probably going to fail (eventually) because of the soil pressing from behind (unless it is engineered-meaning expensive!). It will, however, take a few years to fail if you put gravel behind the new wall. That's the bad news.

If you build two smaller walls (18" to 24") and place one behind the other, in a step up fashion, they will last a long time if constructed with a good foundation and good drainage. This will require a lot of fill and truck loads of gravel for a 130' wall. The walls need to be 3' apart.

I got out the calculator and that is 29 yds (or 5 dump trucks) of soil to back fill a two wall set up. I won't scare you with the gravel figures, but, it would be less.

As I said above - you can go ahead with the block wall backfilled with gravel as you mentioned in your post. Just remember to give the new wall a good base and it should last you 15 or more years.

Here is a $16,000 set of walls with steps that I built in 2000 (I had a helper :-)

The above was my biggest (and last) rock wall. Most of my jobs looked like this before>

And this was after>

Thanks for the response. I think your work looks very nice. Unfortunately, I can't really do the staggered wall solution due to the narrow depth of my rear yard, it is wide but not deep. May need to call the pros... dang.

You can leave the wood in place. You can put a stone retaining wall up behind the wood wall. 3 ft. isn't really that tall. If you want they make metal connectors that go between the retaining rocks and help add strenght. Any lowes or home depot has them and the block is $2-4 at best. I would get a pesticide spray form them as well and take care of those bees first. Carpenter bees will hollow out the wood and reduce it's overall strenght. It's not that big a project but it will take time.