Application of jet grouting on the various contracts in the Lower Inn Valley / Anwendung des Düsenstrahlverfahrens auf den verschiedenen Baulosen im Unterinntal

The jet grouting process is being applied in a number of ways never attempted before as part of the four-track improvement of the Lower Inn Valley line. In addition to the production of waterproof invert, ground improvement to reduce settlement and for the homogenisation of the excavation cross-section in mixed face sections, special mined solutions in particular have been made possible by jet grouting. A horizontal jet grout screen for advance tunnel support was produced for the first time under compressed air conditions; the protection of a complete ringshaped jet-grouted surround also made a mined compressed air drive possible. The jet grouting process was also used to carry out sealing blocks to enable the mined connection of various mechanically tunnelled rescue tunnels to the main tunnel driven by a TBM.
The specific conditions on the project combined with the difficult ground conditions typified by Inn gravel sediments, dejection fan deposits and man-made fill demand all the knowledge and ability of the parties involved. The successful application of the jet grouting technique under these conditions assumes a very high quality of construction and a specifically adapted quality assurance system. Using the example of the contracts H7-1 Fritzens Tunnel, H4-3 Stans Tunnel and H8 Jenbach Tunnel, the various applications of the jet grouting technique are described, and also the difficulties that arose during construction.