Structural design models for tunnels in soft soil in use at present in different countries

Tunnelling is foremostly an empiri- cal technology. Nevertheless, the engineer needs theoretical models for the structural behaviour of the ground and the tun ne 1structure in order to find the best tunnelling method and the most economical de- sign. At the time of tendering the engineer must rely - besides ex- periences - on a model from which he may derive criteria whether a design is suitable, safe enough and economical too.