The grandparent didn't say anything about reinforcing the TBM-made tunnel, it just asserted that it would be controlled. What techniques would be used for "increasing structural durability" that are only applicable to TBM-made tunnels?
I would expect a lava tube from a drained lava flow to vary greatly. We see many have collapsed over the ages. It would provide an insulated underground tube miles in potential extent. That said, the danger of a roof fall would be low in some spots and ready to fall anytime in others. This is still rock, about 6 tonnes earth mass per cubic meter (one tonne on the moon). That means a very strong tunnel liner is needed. It also needs to be air tight. Research into the use of regolith as an ingredient of a concrete needs to be done. One traditional concreted mass is baking bricks of regolith. More research into brick baking from various lunar materials is also needed. A blown up fabric habitat would work inside this sealed brick tunnel.
Can you do that without water? That would be the ultimate so the little that is available doesn't have to be used in construction materials
With enough energy, one can sinter the regolith together. Using water would be ridiciously expensive, unless some meaningful water reservoirs on the moon are found or an easy way to extract the very little existing water.
Yes, ground regolith and other local minerals might be available to mine - grind to powder, press into a shape(s) that can be Lego'd into the tunnel you want. Sintered blocks are very strong in compression and 1-2 layers will allow long buildings to be made in the lava tubes or on the surface. crushed regolith will serve as insulating berms that embed structures.
There are hints there will be water in parts of the regolith. I am not sure how a water based cement would endure heat/vacuum, or only vacuum cycling - would it crumble? Inner places = less heat, but vacuum is all around. I tend to think that a low temperature melting mineral mix might work to bond blocks - a ceramic solder?
I imagine these bricks will be modeled so they stack easily i.e. legoregolith bricks.
Yes, pressed and shaped they could be baked until they were a strong ceramic load bearing shape that suited wall, roofd, door, ceilings Made with precision molds they would be a tight fit and they could be cemented together with a fusing cement that melted at a lower temperature than the blocks, as water would be hard to find and might fume off into the vacuum. In truth there will be 20-30 years of step by step progress and R&D before we reach the stage of doing this on the moon