garden wall foundation

[gardener]

Hi there. I am planning a low retaining wall 4.5m x 0.5m high in my terraced house's garden. It will incorporate a step down from a planting area to a dining site. I am proposing a curved facing wall (4.5m) of yorkstone walling bricks on the lower side and backed with a separate straight wall (4.3m) of breeze blocks and rubble/gravel on the higher side to take the weight of the retained soil. I have dug a single trench, which to allow for the curve is around 1 m wide. The earth is relatively soft, non clay but I have now hit hard ground 30 cms down. There are no trees or houses within 5m of the site. Any comments/assistance on the following points?
1. hardcore base to the foundation - how deep does this need to be? I was thinking 50mm but am not sure this will be enough.
2. how deep should the concrete be? I have seen 150m mentioned eleswhere but this seems excessive for what I want.
3. Given the depth and width the trench, can I lay the a couple of courses of breeze blocks on their side (underground) on top of the concrete before laying the bricks/blocks in the usual way?

Thanks for your advice.

[thedoctor]

If you are on solid ground there is no need for hardcore. Concrete to foundations should always be a minimum of 150mm thick. This is not because of what is going on it but because the ground moves with heat and cold variations and this thickness is the minimum required for it all to stay together...Even then there are no guarentees. You can lay them any which way you choose !