TBM modification for challenging rock conditions - a progress report of the Niagara Tunnel Project (NTP) / TBM-Umbau unter schwierigen Gebirgsbedingungen - ein Baubericht über das Niagara Tunnel Projekt (NTP)

The Niagara Tunnel Project (NTP) is a 10.2 km long bored pressure tunnel that will run under the City of Niagara Falls from the Upper Niagara River to the Sir Adam Beck Power Station. The completed project will enhance the capacity of the Sir Adam Beck Power Station by adding 500 m³/of water per second through the new diversion tunnel. The paper describes the project in which the world's largest hard rock TBM at 14.4 m in diameter is being used to excavate the tunnel. Features of the project include the use of a complex logistic system that allows different work steps simultaneously and describes the site installation for intake as well as for the outlet structures. The paper will also discuss the optimization of the TBM system as the tunnel advances through the varying geology consisting of various horizontal banked shale layers.
In order to meet the aggressive construction schedule as requested by the client, the contractor decided to assembly all mayor equipment including the TBM without a workshop assembly. The tunnel boring operation began in September 2006. After a start-up and commissioning period of four months, the production increased steadily through the various rock formations of the Niagara Escarpment into the Queenston Shale. Tunnelling through the Queenston shale proved to be far more difficult than expected with key block failures up to 20 t and over break exceeding 4 m in numerous occasions. The paper describes the design and construction methods to handle these extreme conditions with a big diameter open type TBM. Completion of the project is foreseen for 2012.