Once land on the west side of Manhattan had been cleared of old tenement buildings, engineers excavated a construction shaft to provide vertical access to tunnel operations, including staircases on one side and electrical cables on the other for electricity and pipes carrying compressed air to keep the Hudson River from rushing into the tunnel. Within this shaft, workers known as “Sandhogs” assembled the cutting shield, weighing over 400 pounds, to initiate the burrowing beneath the Hudson. Holes were first drilled at the face of the tunnel, and then the drill holes were loaded with explosives and detonated.