Nov 20, 2020 2:09 pm
We had a colorbond fence built with the retaining wall plinths built into the fence, these things: https://www.teamworkfencing.com.au/colorbond-plinths/. The plinths are 15cm high, and at the tallest point there are 5 plinths and then the 1.8m fence panel on top. This means the post holding up the fence is 2.55m above ground and then however deep below ground. The sand is loaded to about 50cm inside at it's highest point. For almost all of the length of the fence (50m on each side and 20m on the back) there is nothing on the other side, the level is in the lowest plinth.
The problem we have is that although this is working to hold the sand, the system won't work with any load on it. Anything that puts pressure on the fence bends the fence post in the neighbour's yard, which also puts the fence on an angle. This means the sand can't be compacted to build a path and one one side we want to build a driveway, which needs to be compacted hard and also have the driveway load as well.
I spoke with an engineer who said that instead of redoing the entire fence, which would be epic (and involve the neighbour), I can put limestone blocks inside the fence and build on top of those, since they can carry a massive load. They would need to be started in the ground at a point lower than the soil on both sides, so it can be compacted, and then they are placed on top. Since they would be at the lowest point, there would then be no pressure on the fence at all, so all of the load would be inside the blocks or in the case of the driveway, inside and above the blocks.
I have since lost contact with the engineer, but needed to clarify a couple of thing - I am hoping someone here might be able to help.
1. Do I need to run a footing around the base, or can they just go on compacted sand? On the side where the driveway will be I don't want movement to crack the driveway, but wasn't sure if I need to go the extra step of a footing.
2. Do they need to be mortared or do they just sit on top of eachother?
I plan on using 50x30x20 blocks, about 90kg each.
On the inside, I need to rise up about 40cm up the plinths and then allow for the 10cm of driveway on top.
I think the answer to both questions is yes, but wanted to avoid the expense if I can.
I didn't know when this was originally done that it would be so useless later and would never have accepted it (I'm still amazed and disappointed they recommended it), but this is what I have to work with.
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