This paper discusses the behavior of a small drill and blast tunnel and two shafts in hard rock under a running river. Rock reinforcement design was based on the Q-system combined with numerical modeling and consisted of friction rock bolts and shotcrete. During construction RMR was used to check the adequacy of the designed tunnel support. The entire tunnel has been safely and successfully excavated and a cast in place concrete liner was placed in October '09 against Wisko waterproofing. Completion of the project is scheduled for late spring 2010.

1.1 General

The Harlem River Tunnel is a 700 ft (213 m) long utilidor, which is part of a new 9.5 mile (15.3 km) long 345 kV underground transmission feeder, running fromYonkers, NY to upper Manhattan. Details of design and planning issues were previously discussed in Mooney et al 2008 and Stypulkowski et al 2009. For the first time since the NYC water tunnels were build over 40 years ago, a new tunnel has been constructed in the Inwood Marble. Historical evidence from tunneling done in the late nineteenth century pointed to difficulties encountered at contact zones between the Inwood Marble and the other formations. In these contact zones, the marble tended to be sheared and badly weathered. When penetrated, water would flow in along with streams of chloritic sand. No evidence of contact or presence of chlorite filled zones was discovered during the geotechnical investigations for this project. However, they couldn't be ruled out and the risk had to be addressed since the horseshoe shaped tunnel with an 18 ft (5.5 m) span would have to be excavated using non-TBM methods.

1.2 Contract Documents Summary

All bidding contractors were required to attend a pre-bid site visit to obtain information regarding the existing site conditions.

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