Underground cities

Abstract

Space is a rare commodity in the built environment. This drives urban developers to seriously explore the underground as an option for urban expansion, at least for some speci fi c facilities. For many centuries underground and cave cities have been constructed at scattered locations around the globe, particularly in harsh climatic zones. Underground urban expansion was strong in Canada (Montreal and Toronto) in the 1960s-1990s, and today such development is booming in China. This goes in parallel with rapid improvement of tunnelling techniques which have become cheaper, safer, and faster. Together with economic growth and vision, these improvements have supported signi fi cant expansion of underground facilities particularly in Japan, Italy, and Norway and in China which is now the world’s leading nation in tunnelling. One of the boundary conditions for safe underground development is proper knowledge of the geoscienti fi c conditions of the subsurface. Since subsurface information can now be rapidly digitised, stored in databases and coupled with GIS in many countries and cities, geological and geotechnical information has become more accessible, and more detailed interpretation of subsurface characteristics has become possible. With regards to the future, this chapter describes four global developments and trends (population, urbanisation, quality of life/economic growth and environmental awareness) which, in combination, will probably contribute to increased urban land prices. A fi fth trend (progress in science and technology) will make the underground more accessible as a feasible option for urban expansion and reduce uncertainties in geoscienti fi c modelling. However, psychological barriers and legislative restrictions may frustrate or delay further underground expansion. With time, these will be overcome in places where the need for such development and the bene fi ts for society are greatest.