Wow, that is really close to the retaining wall - how do you manage to keep that safely dry?
Well, the steel must definitely stay properly encased in concrete.
The old wall remains. It is quite uneven and irregular. Each part of the building was simply built into the hill as far as possible using muscle power. Disposal and slope retention were saved + a new wall for the garden.
In front of it will be a new wall made of waterproof concrete (white tank). Between the new wall and the old wall there will be insulation. The rest will be backfilled.
The concrete wall will be 20 or 22 cm thick if I remember correctly.