The scope and opportunity for underground infrastructure to be part of how urban fabric can be more resilient – and so remain intact, functional, capable and operational – is discussed and explored in a report published last year by the International Tunnelling and Underground Space Association (ITA).

Strategies to “keep cities liveable” are vital as the urban population expands along with its needs and wants the fundamentals afforded to a society by in civil engineering – the mass services of clean water, safe sewage removal and treatments, efficient transport networks, and adequate and robust energy supplies. The infrastructure has normal challenges of investment and upkeep but some areas and cities may have additional pressures on their stability and functioning – perhaps from natural disasters, such as flooding, or gradual shifts in the design benchmark thresholds, arguably from risks such as anticipated longer-term trends from climate change.

There is no stasis. All require investment. Moreso, strategies. And these can only be outcomes of awareness, research, engagement and political economic discussions.

Typically, though, their timelines stretch way beyond that of political election cycles and, sometimes, even the length of time some leaders, ministers, official and even governments hold sway with their outlook.

As ever with civil engineering, its deliverables are for longer-term societal vision and benefit. Often short-termism in developed nations can become complacency, being blasé – blind even, to the benefits brought by the majority of infrastructure. The main case of development has been won long ago, it seems; additional investment can end up a marginal argument.

Except, that is, when problems hit; then, systems with under-investment and maintenance or designs that suited prior times, or there being change in growth rates or environmental settings, feel the strain, perhaps to points of being damaged, at cost.

Hence, the notion of resilience emerges moreso than in the past and is being increasingly discussed – although the topic isn’t new, only one that is coming to the fore for richer nations. In the less developed world the value of infrastructure is much more the subject of discussion, along with funding – and the desire for the assets to remain functional for the investment made and debts being repaid – and, hence, resilience is of importance to those communities too.

Resilience should be a design and operational fundamental anyway.

Even so, tunnels don’t necessarily jump to mind for the public of the developed world, the strategic assets being out of sight at the best of times – except for those publicly accessed, such as transport tunnels, or drainage networks that are full beyond their capacities and may leave some roads and streets flooded.

As such, the question of resilience must be actively approached and engaged with by the underground space community.

ITA’s report, ‘Urban Underground Space for Resilient Cities’ ‘(ITA report No32, 2023) is the latest discussion to do so from the international tunnelling body, via its Working Group 20 (WG20): Urban problems, Urban Solutions.

This report follows on from two prior reports that gave some consideration to the challenges and possible strategies around the theme of effective and robust approaches for creating and ongoing use of underground space. The report have come out at approximately 10-year intervals: the last was last year; ‘Underground Solutions for Urban Problems (ITA report No11) was issued in 2012; and ‘Why Go Underground’ (ITA, Godard) came out in 2002.

In discussing urban resilience, in opening the latest report defines it as “the ability of a city, including its infrastructure and inhabitants, to survive, adapt and grow in the face of challenges, both expected and yet unimagined.”

Through an Executive Summary, seven chapters, a bibliography and at a little over 60 pages, the ITA report is well illustrated and packed with examples to focus points of discussion around climate change, earthquakes, tsunamis, floors, population growth and urbanisation, and need for sustainable systems while considering possibilities around reuse and repurposing.

To further quote the report, in its opening Executive Summary, “…the planned, sustainable, and resilient use of both surfaces and underground space is of the utmost importance…”


Many major cities across the world are located in costal zones as they began and progressively grew where rivers open to the sea. The report notes that such coastal cities “are particularly vulnerable” to flooding due to climate change and will need special attention due to risk of general sea level rise as well as suddenness of flood events.

In terms of earthquake risk, though, the report observes, “Underground structures are proven to be resilient against damage” – but flooding is a risk, again especially in coastal zones.

On more regular, events pressures from nature, tunnels are better off than surface assets in that they “are not affected by inclement weather” and have lower exposure to de-icing chemicals and free-thaw cycles, adds the report.

It goes on to say that tunnels, in their creation, bored tunnels by type are overall typically less disruptive to urban communities than with the construction of cutand- cover tunnels.

Aside from some degree of short-term disruption during construction, the report adds that the very goal of placing transport linked below the ground surface in busy, densely-built urban settings “promotes the preservation of existing communities, environmentally sensitive areas, and parks, as well as historical structures and cultural heritage.”

Further, it says “The use of underground space… is an important aspect of compact cities” but to do so successfully requires “conscious and continuous cooperation between citizens, city planners, construction experts and policy makers.”

While it is one thing to undertake fresh whole excavations to create new assets below the surfaces, the report points out that another strategy to help use the underground space of a city for public benefit is to effectively remodel some of the tunnels and subterranean openings that may have been previously built or opened up for other purposes. Some such spaces could be the likes of abandoned mines, decommissioned military or industry facilities, parking or storage spaces, and also unused or unused civilian shelters.

“Cities that have embarked on reviving and repurposing such facilities have improved the resiliency of communities and often realise a more compact and efficient city in the process,” adds the report.

So there is a variety in creation of underground space, and shape and form, and purpose and possible reuse below cities. It is that diverse range that can be part of how tunnels support the robustness of the urban environment to take blows and withstand and rebound. Resilience. The report says, then, that utilising underground space helps by “improving the sustainability and resilience of cities.”

There is the rider, though, that a long-view perspective is needed and, “Allocating necessary funds can be supported by wider campaigns promoting and demonstrating the numerous advantages of underground solutions and the increase in urban resilience they bring”.

Taking such long-views, and refocusing on the greater and higher vision of civil engineering is – including the tunnels it creates, enables infrastructure to be resilience “as a necessary priority” for cities.


In case study examples, briefly explored, the report looks under various headings at complex public, commercial, retail and transport environments in ‘compact cities’, such as in Asia and North America, and leisure and spiritual, such as in northern Europe.

It notes underground shopping centres and transport hubs in Canada, Japan, South Korea and China connect surface buildings with below surfaces commercial spaces, pedestrian walkways and rail/metro networks, and create extended indoor areas.

Examples of extensive pedestrian pathways in through tunnel networks are cited for Chicago, Toronto and Montreal, respectively, all those routes being links to a networks of subsurface nodes, such as office towers, hotels, department stores, parking facilities, transport stations

The report also mentions the below ground assets for leisure and religion in Helsinki, such as an underground swimming pool and also a hockey rink, plus a church.

Many of the cities with extensive public, business and spiritual spaces below ground are in northern latitudes with harshly cold climates over prolonged winter seasons. The subsurface facilities and routes enable more of life, socialising, business and economic activity to go on despite difficult weather conditions above ground.

But it is not only about the norther latitudes. The report observes that Milan, like Helsinki, has plans for further upgrades to its urban space that include underground development in the master plans.

“These developments are promising and will be landmarks to a sustainable urban future.”

But building underground is not enough in itself.

The long-view requires the underground assets to be resilient in themselves and operate such that they are integral to the functioning resilience and economic life of an urban society. As such, the reports cited case studies where assets are at risk of flooding as climate patterns are seen to be shifting, record-breaking weather events may occur, and urban populations and areas have been expanding.

Some of the cases discussed, where designs have sought to deal with such risks, include: the Maldonado Tunnel project in Buenos Aires, completed in 2013, to double the drainage capacity in the city; the MAUDC drainage system in Tokyo; initiatives in Rotterdam and Copenhagen; subterranean reservoirs below Madrid; stormwater collection at Vistula River in Warsaw; the SMART road tunnel project in Kuala Lumpur, which is able to switch operational mode by stopping traffic and instead providing flood mitigation storage; and many more.

While the dual-mode design enables water to enter, major risk is presented to flows entering other underground infrastructure, such as rail and metro stations and networks – “with floods or tsunamis entrances and tunnel portals make these systems extremely vulnerable.” In The Netherlands the NoordZuidlijn project has penstocks at each end of the submerged tunnel sections to block off the entrances; in Bangkok there are metro stations entrances built higher than general ground surface level.

Also on the coast, New York is discussed in terms of the large-scale flooding experienced from storms in 2012 and 2021 that exposed vulnerabilities of the city’s tunnels and metro, and subsequent works undertaken to safeguard them and improve the overall resilience of the systems.

Again in the risky coastal areas, from the experience of the 2011 tsunami in Japan post-crisis surveys said there was no confirmed direct damage to underground structures but debris affected electricity, gas and water supplies. But on the underground infrastructure, conduits and manholes suffered less damage than destruction experienced by above-ground assets, such as utility poles. The report says that “installing infrastructure underground is highly effective against tsunamis and the secondary damage they cause”.


The report closes with notes on a number of key points, saying that:

  • Use of underground space is important to planning and realising the creation, and maintenance of, compact cities such as with extensive networks of passageways and large numbers of openings that form warrens, or human hubs for below surface human activities of different kinds, from retail to social and more.
  • Use of the underground can help cushion against environmental extremities, such as noise and also temperature variability. However, there is vulnerability to “the impacts generates inside, such as fires, and internal flooding due to groundwater infiltration” or uncontrolled inflows from excessive surface-level flooding.
  • Ageing underground infrastructure assets may, in addition to spend for their upkeep, may “require adaptation to extreme weather events and natural disasters”, with the further observation that they would most likely also precede climate change concerns and that would also need to be integrated to upgrades, refurbishment and improvements.
  • technological development can support larger diameter tunnels that would offer more opportunities for multi-functional uses within the same valuable footprint, or subterranean corridor, such as to “combine different transportation modes…or combine road tunnels with storm overflow channels”.

The ITA report ‘Urban Underground Space for Resilient Cities’ (ITA report No32, 2023) is dedicated to Harvey Parker, past President as well as a former member and tutor of WG20.