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?
In our case, the architect insisted that only compacted crushed stone be used for backfill in all areas around the house where paving or patios were subsequently planned. Anything else, he said, would lead to even more subsidence. And that's why we used material by the ton.