The diameter of the vent shaft is substantially larger than you might be thinking. The current (revised) works plan to use a raise-bore reamer of 3.8m(!) in diameter (i.e. down slightly from previous 4.0m).
Watch this video to get an idea how raise boring works. It should be enough to answer your "meet in the middle" question.
PAN Price at posting:
8.8¢ Sentiment: None Disclosure: Not Held
