Abstract: Arcuate concrete segments of a tunnel lining are joined together by means of a recess in a segment edge having a pair of abutment members projecting into the recess to define a constriction therein, the abutment members forming a pair of abutment surfaces facing inwardly of the constriction, and a screw-threaded headed bolt in an adjacent segment, the segments being positioned edge to edge with the bolt inserted in the recess and moved relatively to each other so that the bolt head engages the abutment surfaces. The recess is accessible from inside the lining to allow the bolt head to be tightened.