Since March 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, the authority stated.

"This is a very significant milestone for the East Side Access project, said Michael Horodniceanu, president of 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."

The contractors, a joint venture of Dragados USA and Judlau Contracting, 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.