Second Avenue Subway - New York, NY

GZA provided engineering services for design of the proposed Second Avenue Subway along the east side of Manhattan. The project is approximately 8.5 miles long and extends from 125th Street to Hanover Square.  The new line includes sixteen new stations, renovation of an existing at 63rd Street and two tunnels.  A connection to the Broadway Line at 63rd Street will also be provided.

GZA staff were responsible for developing work plans and analytical approaches to a wide variety of engineering issues varying from rock tunnel design and construction, cut-and-cover techniques, soft-ground tunneling, to building underpinning and protection. GZA staff also prepared Geotechnical Data reports, several Geotechnical Interpretive Reports, and Geotechnical Baseline Reports to support the design effort of tunnels, subway stations, and ancillary structures.

GZA was responsible for all geotechnical aspects of the project, including development of the subsurface exploration and laboratory testing program, project design criteria, specifications, technical drawings and reports. Seismic design criteria were established for all of the underground structures.

Services included: geologic study, buildingfoundation research for the 1,400 existing buildings along the project corridor, development and field supervision of extensive multi-phase soil and rock drilling programs including vertical and inclined boreholes, oriented rock core sampling, soil and rock permeability testing, groundwater observation wells, cone penetrometer testing and borehole geophysical testing.

The subway will be built using one of three fundamental construction techniques depending onsubsurface geological conditions and the geometry of project elements. Most of the tunnels will be built using hard-rock or soft ground tunnel boring machines (TBMs). However, several short segments of the project will be built by cut-and-cover methods. In addition, cut-and-cover construction method is likely to be used for short sections of the alignment which require tunneling close to the surface, such as between existing tunnel segments in East Harlem.

Cut-and-cover will be used to construct ten of the stations and for station entrances and ventilation shaft locations where access to the street is required. Excavations up to 80 ft deep will be required with a few feet of numerous existing building along the alignment. Mining techniques will he used for six stations where bedrock is near the ground surface and in areas where complex underground tunnel shapes such as the intersection of Second Avenue with the East 63rd Street line will exist. Mining is accomplished by drilling and blasting or mechanical excavation in rock and by mechanical excavation methods in soil.

Protection of existing buildings was a major design consideration. Analyses were performed to evaluate the impact of construction on there structures. Where predicted ground movements exceeded pre-established criteria, mitigating measure were incorporated into the construction documents.

GZA worked closely with the EIS Consultant to coordinate the preliminary design documents with the Final EIS.