Excavation expert Alaeden Jlelaty explains how the tunnel boring machine (TBM) under Second Avenue carved tunnels underground. How does a TBM know where it is underground? How does a TBM move forward through a tunnel? How does a TBM remove the muck it has created by excavating? Mr. Jlelaty will answer these questions and more during his discussion about tunnel boring machines at the MTA Second Avenue Subway Community Information Center.