https://en.wikipedia.org/wiki/Grand_Central_Terminal#Platforms_and_tracks
Tunnel-boring machines blasted through the 350 million-year-old rock to carve out the space through which four railroad platforms will eventually be built, two on top and two on bottom.
http://www.theverge.com/2015/11/5/9677300/manhattan-train-tunnel-project-grand-central-lirr-access
https://en.wikipedia.org/wiki/East_Side_Access
