Pregrouting from a TBM. The Follo Line EPC TBM project (Oslo, Norway)

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This paper will be developed under section 4. Grouting equipment. Development of grouting equipment. Norway has one of the hardest rock in the world, with granite up to 350 MPa. The Follo Line Project is one of the most ambitious infrastructure projects in Scandinavia, where four double shield hard rock TBMs have excavated 40 km of tunnel through that rock, from Oslo to Ski. The presence on the alignment of weakness zones and high-pressure water has made this excavation a challenge, as no reduction on the water level was allowed during excavation. 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, affecting the TBM excavation in a much more reduce manner than ever before, and allowing the pregrouting cycles to be fully implemented into the TBMs cycle works. Those innovations are being embedded into a highly complex underground project and it has been possible to minimize environmental hazards and to protect the urban landscape for sustainable urban development.

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