SOME MODES OF DEFORMATION AND FAILURE OF LINED TUNNELS

Lining behavior of three tunnels and two mining drifts is described. One tunnel served a railroad in Colorado and was constructed in sedimentary rock with plain concrete and timber as a lining. The lining buckled in response to vertical and sidewall rock loosening loads. A transit tunnel on the west coast was constructed in mixed face conditions of sand over stiff clay with initial limber support and a lightly reinforced concrete lining. The lining failed in the mixed face segment in shear due to eccentric loading from the differing sand and clay materials having a sloping boundary at the tunnel elevation. Brick and mortar lining was used for storage tunnels in Wisconsin constructed in weak soil and fill. The 150+ years of seeping water exposure and creep, with limited maintenance, led to the collapse of severely-deformed out-of-round tunnels whose linings were nearly strengthless. In a caving-method mine in granitic rock, plain or lightly-reinforced thick concrete lining of modem rail haulage mine tunnels are situated such as to receive very high compressive and extension strains during various phases of the mining activity. Initially the tunnel linings are torn apart by vertical extension, then crushed by vertical compression. The roof remains intact, while the walls crush. In the same mine, blasting energy and vibration destruction of thick shotcrete linings was observed under controlled conditions; it was found that hairline cracks evolved into shears of the roof closest to the blast, and finally, cratering of the roof into the tunnel occurred.