I want to extend an existing wood retaining wall about 8 feet. Design is pretty straightforward. I plan on placing 4x6" vertical timbers on each end, with one in the middle at the 4' mark. Will use three 12" planks for the wall (one buried, two above ground), which is the same as the existing wall.
One question I have is how to join the new part of the wall with the old part. Should I place a new vertical post up against the old post? Or should I try to have the new wall sections attach to the existing post? The existing wall planks are flush with the outermost vertical post, so I'm not sure how I could attach the new wall planks to the old post. If I bury a new post up against the existing post, won't the concrete from the existing post get in the way?
Photos below are of existing wall and the area where the new wall will begin.
I can't see the "whole picture" so to speak, but my advice is to forget about the buried wood wall idea and consider a terrace type wrap around wall built of rocks if you have access to them that is. You can lay them dry . Anything wood in the ground will rot sooner or later. ........sorry, just my opinion.
I'm with Bernie. Even pressure treated wood will not last more than 10 years in direct contact with earth, most wood will only last a few years. Segmental concrete block wall is relatively inexpensive, easy to put in, and looks good, that would be my suggestion. Or you can go with natural rock if you are a drywall fan.
If you absolutely must have a wood wall, make sure you use either a naturally durable wood like locust (maybe you get ten years out of it), or PT that is listed for direct earth contact.