Perhaps if we develop the superfast train then what it would save on construction and running cost may make a profit.Eddy,
With only four terminating stations you may add a couple of billion on for that if you wish.
I used to work at Douglas park 500m below ground and 300m below sea level and it would not be too hard to drive below any coal workings from Parramatta if need be.
Most problems with tunnelling are when you are close to the surface with creeks, water table, soft ground or infrastructure.
Some people may freak out but I can assure you it would be no more scary to some than in a plane that may fall out the sky.
I cannot see cars going 800kph
Before proposing such schemes there are three things that must be considered without even looking at rock samples
1) Cost comparison with other similar projects? A few posts up I showed how far out you were compared to other projects both completed and detail costed. $32B wouldn't get you to Campbelltown.
2) What do others do? No one builds tunnels under flat terrain with low to zero population above and no one uses such technology nor is there even one proposal for such technology over such a distance.
3) What is the problem you are trying to solve? So far not one person has ever answered this in RP when I've previously posted it. The best I can get is people want a govt subsidised railway to undercut the profitable airline industry at the expense of freight and interurban and suburban commuter.