It would seem that anyone who could dig such a hole would also be able to evacuate all the air from it and fall through without any air resistance.
Naturally, through the use of an inner and outer tube, which was used to cool the tunnel with water, enough free steam energy could be had in order to power the earth with no greenhouse gasses.
The time in seconds it would take to fall through and then come back out the top again would be: (2 [Pi] Sqrt[re])/Sqrt[ge]
where re is the radius of the earth and ge is the acceleration of gravity at the surface of the earth, about 5060 seconds round trip.
Of course, you would fall all the way through and just come out the other side before falling back in again.
