What drainage for a small retaining wall?

kippo

I'm planning on building a small red brick retaining wall at the front of my property. It will be double leaf and about 290mm high with the bottom 60mm - 70mm underground (so the wall itself will really only be 210mm high). It will sit on concrete footings and it's length is 10 meters. It will be used to retain a garden bed with a small hedge in it.

Given that this is such a short wall do I require any drainage (i.e. agi and aggregate or weep holes)? The soil in my area is also very sandy.

Also will i have any issues with a hedges root system pushing on it.

EricL

Hello @kippo 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your small red brick retaining wall.

For a small double-leaf red brick retaining wall at just 210mm above ground level and with a total height of approximately 290mm including the buried section, the drainage requirements are generally minimal particularly given your sandy soil. Sandy soils drain exceptionally well compared to clay or loam, which means the risk of water pressure building up behind such a low wall is quite low. In most cases like yours, installing a full agi pipe and aggregate backfill is unnecessary and could be considered over-engineering. 

However, you may still choose to incorporate a few small weep holes at the base of the wall (spaced about every 1.2 to 1.5 meters) to allow for incidental moisture to escape, especially if you notice water tends to pool during heavy rain.

As for the hedge, provided you select a small to medium hedge variety with non-invasive roots such as Japanese box, lilly pilly 'Tiny Trev', or similar root pressure should not be a problem. The wall’s double-leaf construction and solid concrete footing will give it plenty of strength for this purpose. To be safe, plant your hedge 200–300mm back from the wall, and maintain a regular watering and pruning routine to encourage manageable growth above and below ground. Root pressure issues are more likely with large, woody hedge species or when the wall is much higher and subject to greater lateral force from retained soil and moisture. 

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric