In double-lined tunnels, geotextiles are installed between shotcrete and concrete linings to drain ground water that is in the circumferential boundary of the tunnels. During the concrete lining placement, the geotextile often experiences pressures from young concrete on the curved and rough shotcrete surfaces. The pressures are transferred through a waterproof membrane, and act in the normal direction to the curved shotcrete face. The geotextile flow behavior under these conditions cannot be represented by standard geotextile permeability tests. Instead, it requires specially designed performance tests that consider field conditions. A new device to evaluate the permeability of the geotextile in pressurized curved flow channels is proposed; it adopts a flexible loading system and a curved and rough model plate. Testing of geotextiles used for tunnel drainage systems, using the proposed arrangement, shows that the effects of the tortuousity of the flow in pressurized channels affects significantly the geotextile permeability.