User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-75.36.142.53-20140810062120

Ryan was said to be an expert in power technology, and with abundant power from Hesphaetus that could be applied to create various high temperature process ceramics as building materials (perhaps the Ryanium stuff is something like this - something Ryan had created before Rapture existed)

Of course cheap power is useful for making things like glass and processing various minerals in less than economic processes (which wouldnt be used on the surface when cheaper altrenatives exist).

I would suspect that later periods they plausibly could  have built extension areas  underground in tunnels using some high energy plasma cutting/melting tech (tunnel boring machines). Cost effective for things like hydroponic farms made in solid rock and being largely selfsupporting (if not made too largea diameter) and with minimum construction materials/labor required.