Revisions log for question
What to fill the 2 meter deep spaces under the new terrace with?

Underneath the planned terrace is currently a room with a 5K oil tank, which will soon be removed since we are heating with gas. I would like to fill and compact this space (2m deep; 2.5m wide; 3.5 long) in order to later lay gravel patio slabs on it. Now I am faced with the question of a suitable material to fill this space. The terrace should not subsequently sag on the compacted soil. Of course, a separate gravel and crushed stone layer will be made for the patio slabs later.

— According to the Internet, mineral material will definitely do. The most suitable material will be gravel. When compacted, the angular stones will catch on to each other and become stable.

— One acquaintance of mine recommended sand as the material because air pockets are impossible here.

What would you recommend?

• floor
• terrace