Replacing rotted retaining walls

[Morv]

Hello ,

I’ve read through a number   of  the retaining wall posts, and done some research online, but still not sure how to tackle these decaying walls. 
The most immediate problem is the one in the picture with the grey building as that is holding back the pool! 
I really want something that birds (predators mostly), lizards, frogs and insects can use for homes and hiding places. I’d also like it to have plants growing on it too.
As you can see there is significant decay. I’m keen for a relatively cost effective method that is not too difficult as I’m a beginner at this stuff! 
thanks! 

[JacobZ]

Hi @Morv,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Replacing a retaining wall of this size is not a simple task and it is fairly likely you will need the assistance of a professional who is experienced with this kind of work. The basic method will be as follows.

Start by relieving the pressure on the back of the wall. You'll need to dig out at least 600mm behind the existing retaining wall down to the ground level at the bottom of the retaining wall. The volume of material that will need to be moved makes this a job that is best suited to an excavator. At this stage, some temporary shoring may need to be installed to prevent the soil from slipping.

Once the excavation and shoring have been done, you will need to concrete in posts of a suitable calibre for the height of the retaining wall. Ridgi makes a variety of sleeper uprights for different-sized sleepers and different wall heights up to 900mm high. For a wall 900mm high, you would need to use the 1.8m posts and have 900mm concreted into the ground.

Once your posts are in place, you can then install the sleepers. For a natural look like you are aiming for, timber sleepers are the way to go. For longevity, I'd suggest using 75mm thick sleepers or hardwood sleepers.

When the retaining wall has been reinstated, you will need to install drainage gravel and agi pipe along the back of the wall. This drainage will help reduce the hydrostatic pressure on the retaining wall and is essential for higher retaining walls.

After the drainage is installed, the soil can be backfilled to return the landscape to its original state.

This is not a small job so I would strongly suggest you consult a landscaper before making any decisions on what you'd like to do.

Allow me to tag @Nailbag, @Dave-1 and @Jewelleryrescue for their thoughts.

Jacob

[Nailbag]

Hi @Morv 

My advice would be to engage an experienced landscaper to at least handle building the retaining wall near the pool shed. This is the one that needs to be installed correctly and with some urgency. 

In following @JacobZ outline in how to replace the other walls, another approach where possible is to build new ones in front of the old. Then take away the old top level sleepers and backfill with soil to the new ones. 

With this approach you could utilise the landscaper to dig the holes for the new posts and even cement some or all in position. This is the most different part of the project as the posts need to be accurately positioned. 

Then at a more affordable time you can start dropping in the new sleepers in order of importance. 

Nailbag.