Over the last 20 years shotcrete has become the most widely used method of ground support in underground construction in Australia. The reason for this widespread application is the adaptability and effectiveness of shotcrete for both immediate and long-term ground support. Shotcrete is frequently used for temporary support as tunnel excavation is advanced because no other form of support can lock the surface of ground together and prevent it from unravelling in the manner that is possible using shotcrete. Its long-term durability is also outstanding, making it effective as a means of permanent support as well as temporary support. This means that many tunnel linings consist of an initial temporary lining over which a thicker permanent lining is directly sprayed. Alternately, a cast-in-place lining may be cast against the surface of the initial temporary shotcrete lining. Both methods of tunnel lining construction have been used in Australia.

Design of a tunnel needs to consider durability, water resistance, fire resistance, seismic effects, other internal loads and maintainability. The required design life of most tunnel is around 100-120 years.

Design for strength and serviceability of tunnel is more complex than for above ground structures, because the load arising from the ground, and support of the ground associated with the shotcrete lining, are dependent on each other.

Safety in the context of designing tunnels is important. Design should include identifying any possible risks and manage those to be as minimal as possible before construction and operation begins.

For more information, see Australian Tunnelling Society
Also see: Concrete Institute of Australia - Shotcreting in Australia