How strong are gravel boards?

[DIY Muppet]

My garden is approximately 2' below that of my neighbour and the step is currently held back by sloping 2'x2' slabs (been there for forty odd years). At the top of the step is rotten timber fencing which I need to replace.

My thought was that I could remove the slabs, dig out the step so that it;s vertical, and install slotted concrete fence posts of 11' length to a depth of 3' adjacent to the step, thereby giving a height of 8' on my side and 6' on my neighbours side.

If I use this approach and I slide either two 1' gravel boards, or one 2', gravel board in between consecutive posts would the boards have the strength to hold back the earth against them? I suspect that they're not constructed to resist much side loading.

Any suggestions greatly appreciated.

[4213paul]

You can buy concrete sections to slot between post to use as gravel board.
Although not as good looking as wood, these would be a much better barrier for the soil.