Plot with terrain drop - separating wall neighbors - foundation?

We have not yet established the final ground level on our side; we will go down about 70cm more. Now the neighbor at the border has dug a trench, poured concrete into it, and is now building a wall on the border on this foundation with hollow blocks, which he also wants to fill with concrete later.

I’m telling you, every hairdresser understands that this actionism is nonsense in terms of procedure. As long as your excavation and ground modeling work are not completed, you can only build on sand.

If I interpret your description correctly, the foundation of a 1.8 m high wall on his side is 1 m deep in the ground, and on your side 0.3 m (?) – even if the height refers to your side, and only 1.1 m protrudes from the ground on his side (why so much?), I don’t need a calculator to know that it won’t hold.

Take a look through the recent posts; we had this here about a week ago in the form “Duplex, once with and once without a basement.”

You agreed that a wall should be built and no one thinks about discussing the heights? Did you make the decision to dig out 70cm only after your agreement? The foundation of the wall would then no longer be below the frost line. I don’t think that’s a good idea.

We originally agreed he would wait until the final level was established. Then he suddenly started and the construction workers couldn’t be stopped by me. It is agreed that he will build a wall up to the original ground level plus a bit on top for water runoff. For that, a proper foundation is needed. Are there, for example, online calculators for this?

I’m telling you, every hairdresser understands that this kind of actionism is nonsense from a procedural perspective. Until your excavation and land shaping work is completed, you can only build on sand.

If I interpret your description correctly, the foundation of a 1.8 m high wall on his side is 1 m deep in the ground, and on your side 0.3 m (?) - even if the height refers to your side, and on his side only 1.1 m protrudes from the ground (why so much?), I don’t need a calculator to see that it won’t hold.

Take a look through the latest posts, we already had this here about a week ago in the form "duplex, once with and once without cellar".

Basically my point exactly. The neighbor insists that 30 cm of foundation is enough... I’m just looking for something I can present that makes it clear even to non-construction trades what’s going on.

To clarify again:
The wall is entirely on his side. Currently, there is still excavation at the property boundary. Once the excavation on my side is gone, the wall that directly borders my property will still be about 30 cm in the ground. On his side there is soil.

Here is a totally professional sketch:

That will never hold, and a calculator I know, that's called a structural engineer!

That will never hold and I know a calculator for that, it's called a structural engineer!

Is there a recommendation on how to ideally proceed without immediately involving the building authorities? Any independent organizations like the ADAC for cars but just for houses?

I'm just looking for something I can present to him that makes it clear even to trades unrelated to construction what the situation is.

Just let him read along here. Otherwise, his "Leaning Garage of Pisa" will soon convince him :-(