The number of cities is increasing steadily, as are their populations and densities: urbanisation is one of today’s great challenges. Given that we must improve urban design and resource utilisation to achieve concerted, sustainable development: are urban subsurface areas the new frontier for the sustainable city?
One out of every two people now live in a city, and the UN estimates that cities will be home to an addition 2.5 billion people by 2050. Since we have exhausted the horizontal and vertical models of urban expansion, many urban planners, architects, and public policymakers are convinced that urban subsurface areas now provide unexploited potential.
Among the world’s great cities, Toronto is often cited as a model for urban subsurface use. PATH, its 28-kilometre underground network, contains the largest underground commercial space in the world, and is an important part of the city’s economic life.
This network connects offices, underground stations, and shops, thus reducing congestion at street level, and allowing economic activity to be conducted in the heart of the city year-round, no matter what the weather. In North America, where office buildings often already occupy all the surface area available in city centres, such an underground network creates an environment better suited to commerce and pedestrians.
Optimal use of the subsurface always poses a number of development challenges. For several years now, the École polytechnique fédérale de Lausanne (EPFL) has been one of the leaders in creating concepts to use urban subsurface areas sustainably. The researchers there have been charged by the City of Lausanne with creating a methodology for successful subsurface usage planning in light of the fact that underground areas are often already densely criss-crossed with networks (metros, tunnels, water mains, electrical grids, building foundations, etc.).
The EPFL researchers have pointed out difficulties due to lack of coordination between the various interested parties, and to exclusively sectorial use: “Rather than dedicating a specific subsurface area to a single use, which often excludes any other later use, it is better to study whether the area can host multiple, compatible uses.”
They have thus identified 4 types of subsurface resources: geothermal energy, aquifers, developable underground space, and construction materials. With this in mind, they hope to encourage a “multi-use” approach.
The 4 principal urban subsurface resources according to the EPFL
The urban subsurface is a source of architectural dreams, engineering challenges, and public expectation – and it is a new frontier, rich in opportunity for the sustainable city.