ABSTRACT
The purist would probably define a tunnel as a subterranean passage formed without removing the overlying rock or soil. With scant regard for semantics, this chapter will also deal with the type of underground passage which has been constructed by 'cut and cover' methods. It will not deal with those which are so constructed as to be, in effect, long bridges, but will adopt a criterion based on the form of loading and the interaction of the load with the structure. In a tunnel, because of arching effects, the distribution of load onto the lining is a function of the relative flexibility of the lining and the surrounding ground, the timing of the installation of the lining and the nature of the contact at the interface. The loading on a bridge, in contrast, is not dependent upon such interaction. Tunnels carrying drainage and sewage are dealt with more particularly in Chapter 22. Since this book concerns itself with brick and stone masonry, the tunnels on which it concentrates here are those built in the eighteenth and nineteenth centuries to accommodate canals and railways.
