https://twitter.com/BerthaDigsSR99
A link to a photo of the “middle body” of the tunnel boring machine. Looks a lot more complicated than I can imagine. Looks like it would be quite the effort to get men and equipment through this and up to the front of the machine.
Sorry - that is a link to Betha’s twitter page (lots of cool photos). The photo of the complicated “middle body” is from may 14.