A wood retaining wall is a nice addition to your property to create a terraced area. The problem is over time maintenance is needed due to wood rot.
First thing you need to do is inventory on what needs to be replaced and what is connected to that element of the timber retaining wall. At times an entire section needs to be replaced including the vertical support posts and the horizontal retaining wall slats.
Note: All lumber must be pressure treated and all hardware needs to be either stainless steel or galvanized.
Step 1 - Remove Soil
First you need to dig out all the soil behind the damaged section of the retaining wall. The hole should be wide enough and sloped for easy access to work behind the existing section. Prepare an area for all the removed soil. A large tarpaulin spread out will help protect your existing ground cover. Dig out a new trench behind the wall to install new gravel for drainage.
Step 2 - Support Remaining Wall Lumber
If you are removing a post, but not a wall section, nail a vertical piece of lumber to the existing wall planks to hold together and add angled support to hold it in place while replacing the post.
Step 3 - Remove Damaged Lumber
Unbolt the wall planks from the support posts. Remove planks to be replaced. Next dig out around the damaged support posts and remove. Unless the carriage bolts are in good condition, it is advisable to just discard and replace with new bolts.
Step 4 - Replace Support Posts
Fill in the hole leaving a hole 20 inches deep and 12 to 16 inches in diameter. Fill the hole with quick dry cement and set the pole. Running a string line across from the other posts will help you locate the proper height for the post. Use the carpenter’s level for vertical alignment. The use of 2x4 supports will hold the posts in place while the concrete sets. Let the concrete cure for three days to a week before attaching the planks.
Step 5 - Replace Gravel
Add about 6 to 8 inches of gravel into the trench to assist in water drainage. This gravel should be to at a level of 2 inches below the surface. Cover with soil and compact.
Step 6 - Install Planks
Measure the distance from the midpoint of one post to the midpoint of the next. If you are installing to an end post, measure to the outside edge of that last post. With the circular saw, cut the planks to the proper length. Starting with the lower plank, locate in place and with the use of a common nail, hold the plank to the post. Drill a starter hole through the plank and into the post. Place the hole at least 1 inch from the end and edge of the plank and set the second hole diagonally across to the lower side of the plank and 1 inch from the edge of the post.
Place a washer on a carriage blot and screw it into the post. Tighten it to the point where the washer is just starting to penetrate the plank. Screw in the other three bolts into both posts and continue adding planks until the wall is complete.
Step 7 - Backfill
Replace the soil in the hole to be level with the top of the wall. Pack down the soil to compress and avoid any future sinkholes or water retention.