INSTALLING MASSIVE JACKED TUNNELS IN COMPLEX GROUND IN BOSTON

Boston's Central Artery/Tunnel Project has made technical (and Political) headlines many times, and for many reasons over the past years. Over the coming years it will continue to capture headlines. However the successful completion of the three massive Jacked Tunnels beneath the rail tracks outside Boston's South Station, in early 2001, represent a technical success for the Project for which the US engineering community can be justifiably proud. The three tunnels are the largest in the World to be jacked, the ground conditions are just about "as bad as it gets", and the train service passing over the tunnels is one of the most important services in the United States. Many believed that Jacking these tunnels, at best, would not be possible, and at worst, would cause such disruption to the rail traffic, that they would have to be abandoned. However, the co-operative approach to the design and construction of the tunnels between all organizations involved including the designers, the client, the rail operators, and the tunnel contractors - resulted in the successful completion of the jacking, without disruption to any train service. This paper will describe the tunnel jacking operation in general, and will focus on the extremely difficult mixed face, below the water table, ground conditions which were encountered during the tunneling operations, and particularly how the contractor chose to manage the ground conditions.