How to build a small retaining wall?

[Sebastian90]

Hi all,

I’m looking for advice on how to construct a small retaining wall (approx. 40cm high) along the back of my house (see photos). 

• The pink line in the photos shows the planned wall location.

• The green dots indicate existing pipes that either interfere with or limit the depth of footings.

• The blue area will be paved.

• The ground slopes away from the house, and I plan to continue paving on the side opposite the house once the wall is done.

My main questions:

1. Footings and Pipe Interference
   Given the shallow pipe locations (green dots), what’s the best approach to ensure a secure footing? Is a continuous concrete footing required, or would a stepped/sectional footing work where pipes are in the way?

2. Wall Type 
   I’m considering masonry blocks (e.g., Adbri Versawall or similar). Would something like this be sufficient at 40cm high, or would mortared concrete blocks on a footing be more stable long term?

3. Drainage (Agg Pipe?)
   Do I need to install an ag pipe behind the wall? The wall is only 40cm high, it’s a short section, and the slope is away from the house — so I’m unsure if drainage is necessary or overkill. 

4. Backfill & Paving Base
   I plan to backfill behind the wall and then lay pavers. What material would work best for backfilling to support paving — recycled road base? Crushed rock? And how much compaction is recommended?

I believe the soil is a compacted clay and rubble mix.

Thanks in advance for your input — I want to get this right and avoid drainage or movement issues down the line, but also don't want to over-complicate something that could potentially be simple!

[JacobZ]

Hi @Sebastian90,

Looks like a fantastic plan, that you've already considered much of everything you need.

The Versawall system from Adbri Masonry is going to be perfect for your circumstances.

This image, from the Versawall product flyer, shows a typical cross-section and answers most of your questions.

These blocks can be used unreinforced up to 4 courses high, meaning they are well within the limits of your project.

They should be placed on a 450mm wide and 130mm thick foundation made of either concrete or compacted road base. How shallow are we talking with these pipes? Would 130mm of digging expose them?

In terms of drainage, yes, a 100mm socked agi pipe should be installed directly behind the wall with  fall towards a drainage point. This is because any rain that falls behind the retaining wall will press against the back of the wall. This is known as hydrostatic pressure. If it is not dealt with, it can shift the wall over time. As your retaining wall is relatively short, the risk is lower, but it should still be addressed.

Backfilling directly behind the wall and within the blocks should be done with drainage gravel. You can then use compacted road base for your paved section. A paved area doesn't really call for a specific compaction rate. You should just aim for it to be solid enough that it won't move if you stomp on it. Using a Plate Compactor will make this easy.

This sounds like a fantastic project that I am excited to see come to life.

Let me know if you have any questions or require some further guidance.

Jacob