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2016WinterShotcreteEMag

2015 Honorable Mention 55th Street Ventilation Facility By Frank E. Townsend III and Dennis Rubi The 55th Street Ventilation Facility is a critical piece of the Eastside Access Program for the New York Mass Transit Authority. This facility provides critical ventilation for the new tunnels that carry Long Island Rail Road trains to Grand Central Terminal. Unlike most other ventilation facilities, the 55th Street Ventilation Facility, like the 50th and 44th Street Fig. 1: Shaft structure—shot two water barrier panels per shift vent facilities, is designed to be entirely underneath the street’s pavement. These do not have an aboveground component. All vertical elements were shot by Superior Gunite. Superior Gunite installed the shotcrete on a complex, oval-shaped, vertical ventilation shaft, including overhead arches, without the need for forming—saving the general contractor over $1,000,000 in formwork expense. The concrete in the ventilation shaft varied in thicknesses from 24 to 54 in. (610 to 1370 mm) depending on the rock overbreak, as this was a blasted excavation. The base contract volume was approximately 1927 yd3 (1473 m3) with the overhead arch 4 ft (1.2 m) thick using 1277 yd3 (976 m3) of concrete. There were several logistical challenges to the 55th Street Ventilation Facility. Because there was limited access for materials and formwork, the shotcrete process was essential. Shooting the crown of the arch left just 5 ft (1.5 m) of working distance from the final arch, making access very challenging. The elimination of formwork and the ability to access difficult-to-reach areas were key benefits in using shotcrete as the placement method for structural shotcrete in the ventilation shaft and overhead arches. With the fast-paced schedule, the shotcrete method saved the time it would have taken to construct, form, and strip the 8613 ft2 (800 m2) overhead arch. Total time saved on the project due to use of shotcrete was 32 working days. This project ran from September 2013 with the initial lining in the main cavern to May 2015 when the overhead arch and shaft lining were placed. The wet-mix process was used with timely concrete deliveries by the ready mix supplier, Tec Crete Transit–Mix Corp (WBE), who provided a 5000 psi (35 MPa) mixture in the heart of New York City. The concrete was pumped from the surface to the subterranean area of placement with a combination of 2 in. (50 mm) slick line and flexible rubber hoses. Forming on the ventilation shaft was almost completely eliminated except for two-sided sections of the shaft, where a stay-in-place form was used. At some locations, the field measurements for the overhead arch were over 48 in. (1200 mm) thick 38 Shotcrete • Winter 2016


2016WinterShotcreteEMag
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