I had to look this up when you said "specially welded"...
As far as I can tell, TGV tracks are built to vey tight tolerances, but Continuous Welded Rail (CWR) is a worldwide standard on new railway lines, nothing special. I most recently saw some thermite welding equipment just about to be used in Dublin (Ireland) during the laying of new tramway tracks. So there's nothing exotic about the welding process, though it is quite dramatic.
As far as I can tell, TGV tracks are built to vey tight tolerances, but Continuous Welded Rail (CWR) is a worldwide standard on new railway lines, nothing special. I most recently saw some thermite welding equipment just about to be used in Dublin (Ireland) during the laying of new tramway tracks. So there's nothing exotic about the welding process, though it is quite dramatic.