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  Pregrouting Executed from a Double Shield TBM in the Follo Line Project (Oslo)

  The Follo Line project is a unique complex project in Norway and Europe. It is the largest TBM project in Norway and will become the longest rail tunnel in the Nordic countries. With four TBMs starting from the same location, Acciona Ghella JV is jointly responsible for drilling 36 km of tunnels between the cities of Oslo and Ski. Due to encounter ground conditions, it was required the execution of approx. 8 km. of pregrouting. Pregrouting from a TBM is an innovative solution that has never been used in Norway. With this tunnel support technology, it has been possible to minimize environmental hazards, like lowering the pore pressure & ground water level and avoid settlements on surface. This paper will describe the drilling rigs installed in the TBMs, the systematic probe drilling done to detect water leakages ahead of the TBM, trigger values for leakages, design formulas for injection and the maintenance and improvement of the equipment, achieving at the same time good TBM production. The paper will reflect how through innovative and sustainable solutions pregrouting from TBMs becomes a feasible solution even in highly complex underground projects, with the aim to minimize environmental hazards and protect the urban landscape.

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