ABSTRACT
Tunnels are built for transport of people, cars, trains and water, for storage and for mining. They may be deep or shallow, in rock or in soil, in urban or rural environments. They may be built by boring or by cut and cover methods or by sinking them into the bed of a river. In Fig. 25.1(a) the tunnel is advanced by mining the ground from inside the tunnel. In Fig. 25.1(b) the tunnel is constructed as a pair of retaining walls with a roof; the design is really design of retaining walls discussed in Chapter 24. In Fig. 25.1(c) tunnel sections are floated into place, sunk into a trench, connected together and covered by fill.
