The use of underground space is not new. Mankind has always used it to solve problems, taking advantage of its fundamental characteristics. Among the many reasons to use underground space are: land use and location reasons, isolation considerations, environmental preservation, and societal aspects. On the other hand, many problems and issues must be considered when using underground space, including: safety, psychological and health aspects, protection of the underground environment, relations between underground structures and the ground surface, construction techniques, site investigations, risk analysis, assessment of the underground structures, etc. All these issues must be considered in the search of "the optimum use of underground space" and, in addition, it must be remembered that the use of underground space is not an end in itself. Geoengineering considerations influence greatly the extent and the conditions of the use of underground space and this paper indicates some of the geotechnical issues that will become more important as the use of underground space intensifies.
This paper is organized to first review the history and varied rationales for using underground space, then to review interaction of geology and geoengineering design with the planning and execution of underground works. Those familiar with underground space use and the geotechnical design of underground structures will be well aware of most of the issues raised but it hopefully will provide a good review of the reasons why geological and geotechnical input is critical at all stages of the process. In the last part of the paper, particular attention is paid to the trends in underground technology development as well as urban underground space use and what these trends may provide in terms of opportunities for geology and geoengineering professionals to help optimize the long-term use of underground space in urban areas.
