GROUND FREEZING FOR MANHATTAN TUNNEL TBM ESTABLISHES TECHNOLOGY BREAKTHROUGH

摘要

In December 2007, the New York City Metropolitan Transit Authority (MTA)rnawarded a $1.15 billion contract to S3II Tunnel Constructors (a joint venture of J.F.rnShea, Skanska and Schiavone) to extend the No. 7 Subway Line 2.4 km (1.5 miles)rnfrom Times Square to the Jacob E. Javits Convention Center. The two 6.9-meterrn(22.5?foot) diameter tunnels were primarily in rock, except for a 91-meter (300-foot)rnsection where the rock was depressed and the mining operation would encounter arnmixed face condition.rnThe contract required that an appropriate ground improvement method be designedrnand installed for this depression in the rock surface. Ground freezing was selected asrnthe technically superior approach to converting soft, unconsolidated soils to a rock-likernstructurally sound and waterproof material. This project represents the first time thatrnTBMs have mined through artificially frozen ground.rnThe installation of the ground freezing system was completed entirely from thernground surface requiring interaction with city agencies and local businesses. Numerousrnunderground utilities and street intersections also made the installation of more thanrn250 pipes challenging and complex.rnThe paper will describe the design and how factors such as soil properties andrngroundwater flow affect freeze development time. It will also include innovative componentsrnsuch as aluminum pipes and monitoring devices used on this project.