I am such a ninny! I was speculating the roof would become square, and it was in the pictures all the time! They are putting in steel sets pinned to the sandstone. They should do some stress overcoring at the same time! Will they maintain a constant circular lining, or cling to the walls? The concrete lining issues could fill a book!
I was also wonder what the TBM head would do when it hits the abrasive sandstone. Looking at this picture, this is totally a shale machine, not for hard rock. A machine for the sandstone would have bigger disks and larger openings. If the sandstone breaks into round boulders, then it's a lot of steel grinding out!