Sandhogs working on the New York Metropolitan Transportation Authority’s (MTA) East Side Access megaproject have concluded major blasting under Grand Central Terminal, where they are building two enormous caverns 160 feet below street level that will house eight tracks for Long Island Rail Road (LIRR) trains.

Since March 7, 2007, nearly 1,000 employees working 24 hours a day, five days a week, have completed more than 2,400 controlled blasts — all without affecting the nearby operations of MTA Metro-North Railroad or the New York City Subway.

Approximately 857,000 cubic yards of rocky muck were excavated and removed, enough to cover the entirety of Central Park one foot deep.

“This is a very significant milestone for the East Side Access project,” said Dr. Michael Horodniceanu, president, MTA capital construction. “The caverns are essentially now fully excavated. Much work remains to be done to build the platforms and tracks and finish what is currently raw, cave-like space. But we now have a fully built shell in which all future work will take place.”

Each blast was overseen by an FDNY-licensed blaster. To conduct a blast, teams of sandhogs drill hundreds of holes measuring 1½ inches in diameter into the mica-inflected granite schist that forms the bedrock of Midtown Manhattan. Together, the holes are loaded with 200 pounds to 500 pounds of an explosive powder known as Emulex. After the sandhogs clear into a safe area, the Blaster-in-Charge issues a warning — “fire in the hole!” — and triggers the blast.

The contractors, a joint venture of Dragados USA Inc., and Judlau Contracting Inc., are continuing to perform miscellaneous concrete work until their contract is complete in June. They expect that they may need to make additional small blasts that will trim out pieces of rock in the cavern.

In addition to the blasting, the caverns under Grand Central have been excavated in part by two monstrous 200-ton tunnel boring machines that operated from September 2007 until June 2011, chewing through a total of more than 32,000 linear feet of Manhattan bedrock from 63rd Street to 37th Street.