I remember seeing a Discovery documentary named "Extreme Engineering: Trans-Atlantic Tunnel" that precisely details this concept. It's available online in five parts:

http://www.youtube.com/watch?v=frYWTrEfPRs

http://www.youtube.com/watch?v=YKaVQ5Tt_Zk

http://www.youtube.com/watch?v=4zci_6AOCAo

http://www.youtube.com/watch?v=Z2c6vzcmULU

http://www.youtube.com/watch?v=zoPI2doRkgA