Looks like you have created a sump around the roots. The only Acer I know that can take saturated soils is the North American Acer rubrum. I don't suppose it was this species you used?

You would do much better to use a good quality top soil around the roots as this would be a better medium and probably less likely to go sour (bad) if it stays too wet. It would also give the roots a better intermediate before moving into the clay. The heavier (clay) the soil is, the more loam or soil you should use unless of course you completely prepare the site fully beforehand.

Thank you very much. I will dig even more around it and put some top soil.
Have a good week. xP

Hello Paulo.........it depends really in which region of France your house is. As you know the south is more mediterranean so would need the plants of this region to survive, also an irrigation system would be worthwhile. If you are more Northern then you have a great choice of plants of English type...though with heavy clay soil the Acers weren't the best choice. Take a soil sample and have a test done then you know what you're working with and how you will improve it to create your garden. Good luck.