Chapter 4: Technical challenges and assets
Underground construction is much more complex than building constructions at the surface. At the surface, most site-characteristics, such as topography, nature, and drain-age, may be determined relatively easy by visual inspection but underground information may only be obtained indirectly, by excavation, boreholes, in-situ testing, or by using geophysical methods. A second major difference arises from the loading conditions. For surface structures, loading is normally perpendicular to the surface. In the underground, loading conditions of the subsurface materials are more complex (Fig. 4.1) and in three dimensions, and only recently are the mechanics of subsurface loading becoming understood.