Land filling driveway/garage with which material?

Hello everyone,

we have a somewhat difficult plot of land. The original plot was split in the middle and we bought the right half (750 sqm, 21.5m wide, 34.5m long), the left side belongs to my uncle and will not be built on.
The plot is only accessible from the south side (street). There is a slope of about 2.5m over the 34.5m length from south to north. The building application was approved. On the left side is the garage (7x7m) built on the boundary, accordingly the driveway from the south to the garage is 21.5m long.

Now to the main problem:
Since we did not want a pump system but to reach the wastewater sewer normally, the house + garage was planned and also approved to be higher than the current ground level. In the photos you can see the left rear corner of the garage, the marking is the height of the finished garage floor.

What is the best and most stable way to overcome this height difference without building a wall along the boundary? We are allowed to fill/pile/compact the entire left side into the neighbor’s plot of my uncle!!! With what material? How many and which layers? Washed gravel, crushed stone, chippings? The driveway will be approx. 21.5m long x 3-4m wide.

Thank you very much for your help

... but the lifting system is cheaper there

(You need retaining walls up to 1.8 m high at the border). Or slopes at least 1:2

The topsoil and soil class 2 must also be removed beforehand, which will add several more cubic meters.
For the driveway, you then need about 150 m3 of soil class 3 - 4 material. Installed and compacted in layers with a maximum thickness of 0.4 m.

Depending on the load-bearing capacity, a geotextile should be installed under the fill. What does the geological report say?

Just a thought: Garage on concrete pillars and make use of the space created underneath.

(You need retaining walls up to 1.8 m high at the border). Or slopes at least 1:2

The wall was not approved and is not in accordance with the building authority’s requirements. And if the slope is only 1:1, the substructure of the garage won't hold, right?

What does the geological report say?

We don’t have anything like that. It’s not so exact here "in the countryside." Our soil is very clayey, we know that.

The wall was not approved and is not in accordance with the building authority. And if only a 1:1 slope is made, the substructure of the garage won’t hold, right?

But a fill on the neighboring property is approved?

That’s why I recommended 1:2.

We don’t have anything like that. Out here "in the countryside" they aren’t so precise. Our soil is very clayey, we know that.

If I build my house and/or garage on it, you should take that seriously. Who tells you if the soil is load-bearing?

Then, if no soil replacement is necessary, the geotextile is at least highly recommended.

You are sinking a few thousand euros there. Isn’t the lifting system the better solution after all?