I have started to extend a patio to my garden boundary fence on two sides (rear and left as you look at my house. The ground naturally sloped towards the fence on the left which belongs to my neighbour. I removed all the topsoil down to virgin substrate which was 0.2m at the shallowest point and 0.5m at the deepest point where the two fences met. I screwed 19mm marine ply to the fence posts of each fence before backfilling the entire area with MOT Type 1. I then realised that when my neighbours renew their fences this may undermine my patio. I have therefore removed the MOT Type 1 along the fence line to create a trench with the intention of installing a 13.5m long dense concrete block retaining wall. Interestingly the compacted MOT Type 1 on the exposed edge of the trench has a near vertical angle of repose so is self-supporting. My question is whether the retaining wall can be laid on compacted MOT Type 1. A traditional mortar bed would be laid over the MOT Type 1 and the block wall would be laid with mortar joints and weep holes. The plan is then to install a 60mm perforated pipe with drainage sock in drainage stone which will be wrapped in drainage geotextile. The trench will then be backfilled with MOT Type 1 before laying the patio over the top.