Yep, a whole lot of dirt went somewhere.
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Limestone used to build buildings on the surface
That may be, but from the video I saw, the carts/trucks were hauling ground up limestone from the huge drills. But just some water and quick lime, and bricks and blocks are easy to make. And Gaza is mostly flat.
Though much larger, most of the west bank has rockier desert terrain. Tunnel digging is likely tougher.