DRILL-AND-BLAST EXCAVATION OF THE 34TH STREET STATION CAVERN AND THE DERIVATION OF A SITESPECIFIC GROUND TRANSMISSION CONSTANT, NO. 7 LINE EXTENSION, NEW YORK CITY

摘要

The 34th Street Station cavern is part of the No. 7 Line Extension in New YorkrnCity. Drill-and-blast excavations on the project included three 12.2–15.2 m diameterrnrock shafts, a TBM assembly chamber, two pairs of TBM starter and tail tunnels, tworninterlocking caverns and an approximately 300 m long, 18.3 m tall, 21.3 m spanningrnstation cavern with eight penetrations for ancillary adits of various dimensions andrnlengths. Geological challenges included sheared and faulted ground and contactsrnbetween major rock types, however the project benefited from a generally consistentrnrock mass dominated by schist and granite. Many of the inherent problems of tunnelingrnin an urban environment were encountered on the project. Consequently, it was essentialrnto monitor and control ground borne vibrations. Bespoke blasting methods werernintroduced to control blast performance and reduce vibrations in the vicinity of historicrnstructures. A site specific ground transmission constant (K) was refined from previousrnestimates of K for Manhattan bedrock.