ABSTRACT
Tunnels include mainline haulage ways in mines and other important, semi-permanent underground passageways as well as conventional tunnels with surface portals at both ends. Comparison of the single tunnel under vertical and horizontal loading reveals the fact that compressive stress concentration is noticeably less when the long axis of the cross-section is parallel to the direction of the major compression before excavation. Traditional tunnel support in civil projects is by structural steel segments bolted together to form steel sets that conform to section shape. Yieldable steel sets and light segment liner with backfill are two support methods that are often used "squeezing" ground where large time-dependent displacements are anticipated. Estimation of stress concentration for tunnels is similar to that for shafts. Thus, major features of the problem include: cross-section shape; aspect ratio; pretunnel stress field; and orientation of the tunnel axis.
