Abstract: A sealing means is provided for sealing against passage of liquid between two surfaces, as between the tail-piece of a tunnelling machine and the tunnel lining to prevent ingress of working liquid into the tunnel workings, said sealing means comprising a mount for flexible fibers projecting brush-like therefrom, the mount being fixed in substantially liquid-tight manner to one said surface, such as that of a tail-piece, and arranged to permit said fibers to extend into contact with the second surface, such as that of the tunnel lining. The free ends of at least a portion of the fibers preferably extend parallel with the second surface and in contact with one another and/or that surface. Flexible sheeting may be arranged in combination with the fibers substantially to close off said space and inflatable air-bag means may be interposed between the free ends of the fibers (fiber/sheeting combination) and the first surface to increase the pressure of contact between the fibers and the first surface.