Abstract: A collapsible concrete tunnel liner section formed from a number of arcuate segments each connected together by hinges to form a closed loop. In collapsed condition the segments are arranged in a compact stack having a cross section less in its maximum dimension than the internal diameter of the erected liner section. Typically the stack has the appearance of a figure 8, having upper and lower cavities. Air bags are located within these cavities and are expanded to expand the collapsed tunnel liner section into its erected condition. During the expansion the liner section passes through an oversized condition before assuming its final erected condition. This ensures stability for the erected liner section. After erection, grout or other filler material is inserted between the liner section and the wall of the tunnel.

Abstract: A collapsible tunnel liner section formed from a number of arcuate segments each connected together by hinges to form a closed loop. In collapsed condition the segments are arranged in a compact stack having a cross section less in its maximum dimension than the internal diameter of the erected liner section. Typically the stack has the appearance of a figure 8, having upper and lower cavities. .[.Air bags.]. .Iadd.Expansion means .Iaddend.are located within these cavities and are expanded to expand the collapsed tunnel liner section into its erected condition. During the expansion the liner section passes through an oversized condition before assuming its final erected condition. This ensures stability for the erected liner section. After erection, grout or other filler material is inserted between the liner section and the wall of the tunnel.