Until now, segment-lined tunnels in low mountain formations have been constructed with one layer of pressure-tight lining, with sealing being provided by elastomer gasket profiles. The application limit of this method of construction is about 5 bar. If the water pressure is higher, a much more elaborate and thus more expensive double-shell construction with an additional drainage layer between the inner and outer lining is necessary. In the recent past, a solution for this problem in mechanised tunnelling with segment lining has often been discussed in the specialist world: a drainage layer of permeable material for annular gap grouting. This would then make the installation of an additional inner lining with drainage layer no longer necessary.