Infiltration of rainwater into clay soil

Don't worry about the house, the soil conditions have been taken into account. Filling in a bit around the infiltration trench as the landscape gardener suggests is enough. Then don't give it another thought.

and I keep wondering what it might look like under the trench :eek:

Hello, we moved into our new building last year and took care of the outdoor facilities this year: terrace, driveway, etc. - and among other things also the infiltration of rainwater (discharge via the sewer is not allowed, infiltration must take place on the property itself).

For this purpose, we hired a landscaping company that installed a infiltration trench (plastic, 6000 liters) for us. The water from the roof/gutters is directed into this and is supposed to infiltrate into the ground.
After the last rainy days, we noticed that the soil around the infiltration trench is slightly sinking. Digging up the area showed that huge cavities have formed in the soil around the infiltration trench. The landscaper now says he wants to fill it with soil as soon as the soil is completely dry.

Until now, I have never dealt with topics like soil composition, etc., but after this incident I researched a bit more closely: our soil is very clayey. According to the soil report, the soil mainly consists of glacial moraine - and as I have now read, this is not infiltratable at all and basically absolutely unsuitable for an infiltration trench.

Does anyone have experience with this? What does this mean for the infiltration trench? Will it all eventually collapse completely? Can it become dangerous for the house (the infiltration trench is about 3 to 4 meters away from the house)? Can we leave everything as it is and just fill the cavities in the soil or does the entire infiltration trench have to be removed?

I would be glad if someone could say something about this. Maybe someone has an idea how to save the whole thing.