DE2800605

Flexible tubing for lining tunnel walls, and to be loaded in situ with a filler, to bridge the space between the tunnel sleeve and the rock face, is made from high pressure (low density) polyethylene film, with the following characteristics - inclusion of fire retardant and antistatic additives, tear strength (longitudinal and transverse) >=15 N/mm2, elongation to break of >=450%, a needle penetration resistance >=1.5J and a tear propagation resistance >=17N/mm. The tube is laid at intervals over a slatted structure covered with a layer of flexible film, and inflated to provide a buffer support between the leading section of the tunnel sleeve and the crude tunnel wall. As successive 10-50 m sections of the sleeve are added, the spaces between the tubes are filled with e.g. concrete, fine rubble, etc. to provide a permanent interlayer for spreading the pressure of the tunnel wall uniformly over the lining structure. The pressurised tubes adapt to the crude wall surface without puncturing to provide initial support and exclude entrapment of explosive gases and allow infill materials to be promptly cast without contaminating the working face of the tunnel.