Underground space can be defined as space below natural ground level
which can be used as an alternative to an above ground location. While
many of our above ground structures inherently involve underground
excavation for foundations and services, the term underground space
specifically refers to organised development of underground openings and
of the underground domain. For example, the services to a city such as
power, gas, sewerage, water and communications are installed in a
congested array which usually requires roads to be dug up when the
services need to be accessed. An underground space installation of
services would involve a well planned conduit which is easily accessed
without any excavation. The concept of using this virtually untapped land
resource to the advantage of our expanding cities is gaining considerable
interest in Australia. Overseas, in the Scandinavian countries and some
Asian countries, underground space has been used for centuries; in Great
Britain, France and the United States of America over the last century and
in Japan for over a decade. This paper focusses on the types of underground space usage which
should be competitive with above ground use and suggests areas in which
the competitive edge may be improved in favour of underground space. In
particular, considerable advantage is seen by using well-planned
underground space developments in major cities, where the strategic
central location of the development takes advantage of proximity to
potential users. However, the largest single factor affecting the acceptance
of underground space is the high capital cost of construction, even though
an underground space development may result in lower operating costs
and reduced long-term maintenance costs. While excavation methods and
associated costs are very much site-specific, the importance of applying
the latest technology in rock breakage, with consideration of ground
vibration, excavation rates and ground support, remains a major challenge
to the development of underground space.