Drainage and earthworks - on the border?

Hello everyone,

the soil survey has shown that 1 m of topsoil must be replaced within a radius of 1 m around the base slab. Additionally, a surface drainage must be installed all around and underneath the base slab.
Now the following questions arise:

[*]We want to build a double garage 9x6 m directly on the property boundary. There is already a prefabricated garage 2.5x5 m on the neighboring property right on the boundary. Excavation cannot be carried out within a radius of 1 m around the garage on the boundary side but only up to the boundary itself. How is the 1 m deep excavation supposed to be done directly on the boundary? A slope cannot be created because of the prefabricated garage.
[*]What is the purpose of the surface drainage underneath the base slab? No rainwater can accumulate there and water coming from the side should be drained off via the perimeter drainage.

A few pieces of information / assessments are missing for professional answers.

Why does the soil report recommend soil replacement and drainage? Seepage water on a slope? Groundwater? Cautious expert ("belt with suspenders"), who commissioned/facilitated the expert?

What does the expert say about what kind of soil should be installed? ...

Tip:
Talking helps.
Talk to the expert, after all, that is what he was paid for.
Talk to another expert (expert/earthworks specialist).
Talk to your future neighbors. They usually know the soil situation best (water in the basement, etc.).

I have attached some excerpts from the report. Of course, I have spoken to the expert several times, but he naturally sticks to his assessment. I cannot judge whether he is a cautious expert. The property is completely flat and is not located on a slope. The neighbors do not know anything.

According to the report, everything is consistent.

You don't want to rely on clay and loam. Whether the gravel thickness is 55 cm or 30 cm I would ultimately also depend on the structural engineer's assumption of the load for the foundations.

The drainage beneath the gravel is, in my opinion, an additional and not unnecessary safety measure. Even if you have the perimeter drainage on gravel level outside, it is by no means a panacea. Water will find its way...

The 1m continuous gravel bedding I see, among other things, as load transfer but also as a support area for the scaffolding. The latter you do not need with a boundary construction.
The former is not that significant for a garage, perhaps strip foundations rather than gravel.

Regarding my above list, the next step would now be to consult the structural engineer. He should, of course, receive the soil report.

For your information: Structural engineer should be made aware of the neighbor's existing boundary construction. Otherwise, "the usual" structural analysis is applied.

ok thanks for your answer.