Exactly. Building landtunnels uses much more material. This material is expensive; a 100KM+ metal twin tube including foundation is fundamentally more expensive

Exactly. Building landtunnels uses much more material. This material is expensive; a 100KM+ metal twin tube including foundation is fundamentally more expensive then a railway. Further, it seems to me the thermal expansion problem (to me the single biggest technical problem) is not an issue either. No wonder Elon Musk started The Boring Company. Once costs go significantly down to bore tunnels, most land on earth can be used to build a highspeed network on.