FEATURE ARTICLE NYC Subway Station Poses Construction Challenges Site plan The first segment of the much anticipated Second Avenue Subway in New York City is under construction. When completed, the segment will operate from 96th Street to 63rd Street, where it will divert west along the existing 63rd Street line, stopping at several stations, including 96th, 86th, 72nd and 63rd Streets. Much of the construction of the two track, twin tunnel subway was completed using a tunnel boring machine (TBM). The launch and retrieving box of the TBM was strategically located at the south end of the 96th Street station where bedrock is approximately 70 ft (21.3 m) below the street level; several feet below the invert elevation of the subway tracks. This enabled the project team to use the cut and cover method for the TBM launch box and the rest of the northern end of the 96th Street station, including the ancillary facilities adjacent to the station. The successful implementation of the cut and cover method of subway construction in the heart of Manhattan required an extraordinary amount of planning to minimize the impact of the subway construction on the community, businesses and everyday traffic. For example: • Careful planning of the main- tenance and protection of vehicu- lar and pedestrian traffic so that streets or sidewalks are partially open while construction pro- gresses in designated closed areas • Tempor a r y or pe rmanent relocation of vital utilities – water, sewers, gas, electric conduits, fiber optic cables, and telephone cables outside the construction zone AUTHORS All these activities had to be carried out under extremely heavy traffic within a limited space, budget and schedule – a daunting task. Utility Relocation In cut and cover construction, the first task is to divert utilities away from the proposed construction corridor. Once the team identified utilities on the schedule’s critical path and obtained proper permits and permissions the utility relocation work was off to a start. One of the most challenging aspects of this project was relocating the existing utilities. In some instances, 100-year-old brick sewers and steel gas pipes were relocated to the outside of the subway structure alignment while maintaining utility service to the existing buildings and neighborhood. This phase involved exposing all existing utilities within the boundaries of Second Avenue and moving or relocating them to within 15 ft (4.6 m) of the existing buildings. Essentially, all the existing utilities, which were spread over Second Avenue’s 100 ft (30.5 m) wide alignment, needed to be moved to within two 15 ft (4.6 m) wide corridors on each side of the roadway. Some utilities were relocated to within inches of the existing buildings along the avenue, which ranged from modern multilevel high-rise buildings to historic tenement buildings more than 100 years old. Due to the proximity of the utility Uncovering existing utilities relocation work to the existing buildings, we employed extra atypical excavation methods and took additional support measures to Sitotaw Y. Fantaye, P.E., Associate, Renzo D. Verastegui, P.E. Supervising Engineer, Mueser Rutledge Consulting Engineers; Pablo LeMus, P.E., Project Manager, EE Cruz Construction Co. Inc. DEEP FOUNDATIONS • JAN/FEB 2013 • 41
