I am building a world where the new world is built on top of the old one, and the old world is kept under a layer of "immigrated" dirt from other worlds via portals.
If there was a portal (or multiple) that was spilling dirt onto our planet, how much would be needed to cover most buildings and vehicles? Skyscrapers and major buildings would be uncovered, and that would be fine. I don't need exact measurements, but rough estimates like "The equivalent of the Moon" would be precise enough.
In addition, what real locations in our world would likely not be impacted as much as others? (Civilizations high up, or surrounded by mountains preventing them from being covered)
Thanks in advance!