Life six feet under

By Stéphanie Rocher, Project Officer  I  Urban planner trainee

The subsoil is an increasingly exploited resource, but not always in the context of natural resource development. The densest city centers of our megacities are seeing their subsoil developed as spaces for living, economic and social activity. All over the world, cities are developing their underground, whether in Tokyo, Paris, Amsterdam or elsewhere. Montréal Interior is a distinctive feature of Montréal abroad. An expression of man’s adaptation to the northern city, a second city lies beneath our feet: with its 32 km of tunnels, Montréal Souterrain is the world’s largest underground network. In addition to the metro system, 80% of downtown offices and 35% of businesses are connected to it. Moreover, the organization Art Souterrain is exhibiting contemporary works of art in the city’s basements until March 16, with the aim of highlighting this architectural heritage. Elsewhere in the world, underground space is increasingly seen as a solution to surface environmental problems and the scarcity of available space. The underground city represents a promising and as yet little explored avenue for the development of saturated city centers.

However, the potential of the underground city remains difficult to assess, deterring decision-makers from making major investments. Yet there are many advantages to underground construction. On the one hand, building infrastructure beneath the surface frees up floor space, an increasingly limited resource. This gain in space makes it possible to set up new activities and create a more compact, mixed-use city.

Building underground remains expensive, and some underground buildings can cost up to five times more than conventional open-air constructions. Despite high construction costs, these investments can be recouped by extending existing premises or in cities already saturated with construction. Certain conditions must be met before space can be made profitable, such as buildings must be interconnected, or geothermal energy for heating and cooling must be properly harnessed. Construction debris can also be sold, and used to stabilize roads, manufacture cement and more.

The Deep City approach

To assess the potential of the underground, a method has been developed by the Swiss Federal Institute of Technology in Lausanne (EPFL): the Deep City approach. This concept provides a global approach to urban underground management and equips urban planners to use underground resources more efficiently. Touching on both engineering and economics, the primary objective of the approach is to propose a master plan that documents the use and value of underground plots. Everything is considered: the 3D space available underground, drinking groundwater, excavated materials that can be valorized, geothermal resources that can be used for heating and cooling, etc. Very few cities have such a plan, as efforts are more often concentrated on the surface. The method cross-references the demand for use of the subsoil with its potential for exploitation. It is thus possible to achieve substantial gains in growth potential by exploiting the first 100 meters below the Earth’s surface for construction projects. The Deep City concept also helps cities to extend their scope of legal intervention underground, in areas that are rarely subject to precise planning regulations.

Four Swiss cities and four Chinese metropolises have tested this method, including the Chinese city of Suzhou, which in 2015 will be home to 5 million inhabitants. Huanqing Li, who completed his thesis at the Laboratory for Research in Environmental Economics and Management at the Swiss Federal Institute of Technology in Lausanne, carefully studied Suzhou’s potential for underground expansion. Three-dimensional maps illustrating the value of the land and integrating environmental constraints were presented to the government.

Leads to follow for Montréal

In Montreal, improving the current underground network would require an integrated framework for planning and managing underground space. The central city needs a master plan, currently non-existent, which would dictate the public interventions to be adopted. A second step would be a general economic study, based on an analysis of socio-economic needs and an assessment of available underground space. Finally, management and administration strategies would guide underground urban planning.

Does this mean we’ll all be living underground? Probably not. But building infrastructure below ground does bring certain benefits that need to be analyzed. The challenge now is to develop our underground in an intelligent way and convince other cities to follow suit.

Source: Kai Wu,   stuak.wordpress.com

Reference: Overney, Jan,  2013. “Too cramped, the city looks down”. EPFL-INTER-REME: École Polytechnique Fédérale de Lausanne, Institute de l’urbain et des territoires, Laboratoire de recherche en économie et management de l’environnement.

Aftes comité espace souterrain, 2012. “Sustainable management of the city’s underground resources: the Deep City concept”. Journal Tunnels et Espace Souterrain, No. 234 November-December 2012. http://www.aftes.asso.fr/doc_gd_public/article_fichier/T234-542_551Deepcity.pdf

CNRS-PACTE-LATTS-EPFL Ecole thématique d’Aussois, 2010. – “A market hidden beneath the city ” Archives ouvertes en Science de l’Homme et Société/Science politique. http://halshs.archives-ouvertes.fr/halshs-00517801

Image: Downtown Montreal, 2021