(In the modern world, this could be solved by founding new cities with better planning up front.)
The local geology is another major issue, so presumably that would be a major factor in the decision of where to build your world city. Various modern cities are built on hard volcanic stone, so digging beneath them is fairly pointless.
The local geology is another major issue, so presumably that would be a major factor in the decision of where to build your world city. Various modern cities are built on hard volcanic stone, so digging beneath them is fairly pointless.