Second bore begun on Second Avenue Subway
Written by William C. Vantuono, Editor-in-ChiefA Tunnel Boring Machine (TBM) has begun mining the second (east) tunnel for New York City’s Second Avenue Subway. Starting again from 92nd Street, the machine has begun carving a tunnel will be 7,800 feet in length, largely (but not exclusively) through Manhattan schist. The TBM previously mined 7,162 feet for the first tunnel.
New York’s Metropolitan Transportation Authority says the second tunnel will include a tight, westerly curve into its existing 63rd Street Station. Once completed, the tunnel will receive the concrete lining which provides the permanent tunnel structure.
During the first 200 feet, the TBM will be mining through ground which has been frozen, a technique which engineers employ to harden soil, or decomposed rock, enabling the excavation process.
Phase I of the Second Avenue Subway is currently scheduled for completion in December 2016, and is expected to carry more than 200,000 riders per day.
