besides the hollow of the tunnel,

its sides still needs to be connected and welded

to the entirety of the structure,

to provide structural stability.

so it would go around the hollow of the tunnel.

if in case anyone is thinking it can

just be interlocked, sandwiched in-between.

but why am i writing this, structural engineers

will figure out the math on this.

Overall, it will be more expensive than

one originally thought, with better, bigger

materials needed. But.

 

Worth it.