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  Innovative TBM Launch Sequence for the Suffolk Coun ty Outfall Tunnel Project

  At more than 4,300 metres in length, the Bergen Point WWTP outfall replacement tunnel was bid with the pressurized face (slurry) tunnel boring machine launched from a shaft and a starter tunnel. The bid documents prescriptively required the use of ground freezing for temporary ground support for the launch shaft and the starter tunnel with a tried and tested approach to machine launching. Post bid, the contractor submitted a substitution to modify the machine launching approach, such that the first 122 metres were tunnelled using a method traditionally used for micro-tunneling, thus accommodating the installation of the trailing gear without the need for a starter tunnel and slow launching process. This paper provides a description of the post-bid evaluation, and eventual acceptance, of the unique method for launching the slurry machine; innovative use of precast pipes to facilitate the machine launch; and, provides the Owner’s and Engineer’s assessment of the benefits, challenges and lessons learned related to the modified approach.

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