How to place soil in garden bed next to concrete plinth?

[JM2]

I recently built a new colorbond fence with plinths to raise ground level from 200-400 mm slope. I added Ag pipe and sand for drainage at the base of the plinth and placed black plastic under pipe and next to plinth.
I plan to plant fruit trees and wonder how and if I should strengthen the plinth before moving soil next to it? I have some extra concrete plinths over that I could use. I understand that it's not a full retaining wall but want to DIY to strengthen if I can.

[EricL]

Hello @JM2 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your concrete sleepers.

Unlike timber sleepers, concrete sleepers do not bend as they are reinforced inside. The majority of the load would be on the support posts at the end as they will be bearing the brunt of the load. However, if you feel that extra support is needed on the other side, I can only suggest using Jack 60cm Ultrapost Premium Steel Fence Post - 5 Pack on the entire length of the sleeper evenly spread. This is of course on the condition that there is space behind the concrete sleeper. 

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

If you have any other questions we can help with, please let us know.

Eric

[Dave-1 · Accepted solution]

Afternoon @JM2 

I was just looking up avbout plinths and what they should hold and yeah you are right its not a full retaining wall but then it still "retains soil" lol Love their definition, "shaking my head"

I dont see a problem with the way the plinths are used and really the tree will send roots out as it grows which will also help hold it in place plus the soil. I would probarlly stay clear of the fence by a meter to give space for it to grow but mainly for the tree to have something solid to bind to teh soil all the way around its roots.

Dave

[Nailbag]

Hi @JM2 

Plinth boards being only 25mm thick are prone to short life span when soil is rested against it. And as @EricL mentioned it will bend. If the level of the additional soil against the shed wall is no greater than 200mm, I would simply install a single height row of 50mm or 75mm treated pine sleepers. Then use 400mm lengths of the same concreted into the ground central to the joins. If greater than 200mm, then a 2nd row and consider Jack 75mm x 750mm retaining wall posts concreted into the ground at the joins.

Nailbag

[JM2]

Thanks @Dave-1 . I've been shaking my head a lot about different definitions and views about retaining walls too.

But what you said sounds good to me. The trees' roots will hold the soil and I'd allow a metre around them for growth anyway. I might put grasses or small shrubs to hold soil next to plinth and leave the 200mm slope as is rather than testing the load by pushing more soil against  the plinth. Appreciate your help!

[JM2]

Thanks @EricL and for bringing in the experts. I know what to do now if I feel it needs extra support. But as you say, the concrete sleepers are reinforced and pretty strong already. 

[EricL]

HI @JM2 

Please keep us updated with your progress, we look forward to seeing the garden bed levelled and ready for use.

Eric