Effect of bolts on failure modes near tunnel openings in soft rock

The Paper elucidates the potential failure modes around a circular tunnel opening subjected to a hydrostatic stress field. Physical models have been tested in the laboratory using a large cubical triaxial apparatus to investigate the effect of grouted bolts on failure mechanisms. Depending on the bolt density, the observed failure of a bolted tunnel can deviate significantly from the theoretical rupture surfaces (log spiral) anticipated for an unsupported circular opening. The influence of discontinuities on the rupture process near the tunnel wall is also explored. It is shown that by use of a high bolt density, the propagation of slip lines and the risk of failure close to the tunnel boundary can be minimized. The failure zone (delineating wedges) around the tunnel wall becomes smaller with increasing degree of reinforcement. L'article s'interesse aux modes possibles de fractu-ration autour de l'ouverture circulaire d'un tunnel dans un champ de contraintes hydrostatique. Des modeles physiques ont ete ex...