Performance of tunnel support under large deformation static and dynamic loading

Abstract

Tunnels under high stresses and deep mining conditions are often subjected to large static and dynamic deformations. It is usually not practically possible to contain the energy involved by means of stronger support. Instead, the support must yield and, in yielding, absorb energy. With yielding support of suitable deformation capacity, it should be possible to contain very severe static and dynamic deformations. Research into the performance of tunnel support has recently been carried out in three areas: (1) the behaviour of retainment support elements such as rockbolts under dynamic loading. This showed that specially designed yielding rockbolts could absorb more than 50 kJ each in yielding some 0,5 m, without showing any damage, (2) the energy absorbing capacity of mesh and fibre reinforced shotcrete, based on the results of static testing of shotcrete panels, and (3) the behaviour of containment support elements, such as wire mesh, wire rope lacing and reinforced shotcrete under dynamic loading. This has shown that the practical capacity of wire mesh alone is about 15 kJ/m 2, but that this capacity is more than doubled when wire rope lacing is added.