The only way is down

Culture is replete with the concept of civilisations living underground. It crops  up in everything from HG Wells to Elizabeth Beresford. Of course, Wells’ underground dwellers were mutated cannibals and Beresford’s were pointy-nosed mammals with an excellent grasp of English and an ecological bent, but the exploration and exploitation  of the realm below the surface has been a trope for decades.

Now, the lure of subterranean space is growing, especially in cities where land is at a premium and building becomes ever-more difficult. And while travelling underground is part of everyday life for millions in cities around the world, other uses for underground space are becoming ever-more innovative; and more may well be to come. The challenge for engineers will be how to construct these underground spaces, make them suitable for the uses earmarked for them and maintain the conditions inside them to keep their contents and users safe and comfortable.

There are many reasons you might want to go underground. Space is an obvious example. In crowded established cityscapes such as London or New York, or the chaotic, fast-growing cities of India and East Asia, there just isn’t much space on the surface. Taking a small ground footprint and building upwards into a skyscraper, the choice for maximising space since the 1920s, has its limitations. In many cities, the planning regimes are increasingly frowning on ever-higher skyscrapers, and even in the Middle East and East Asia, where it seems easier to get permission to build high, there’s a practical limit to how high you can go. Hollowing out the space under the ground could be a way to get around these problems, as it gives more scope to expand laterally, rather than linearly. Go wide, not deep.

Another factor might be an inhospitable outdoor environment. In Canada, the northern states of the US, Scandinavia and Eastern Europe, the winters are so bitterly cold that building underground, where the environment is stable and insulated by the surrounding soil and rock, is an attractive prospect. Similarly, nearer the Equator, subterranean spaces could offer an escape from steamy humidity; and in heavily industrialised cities with air quality problems, it could be easier to guarantee a healthy, breathable environment underground.

But sometimes it’s just a matter of space. In Tokyo, for example, bicycle parking has been taken underground using a system devised by engineering firm Giken Seisakusho, which can store 144 bikes in a space just 7m wide. Bikes are becoming more popular in urban Japan, where  air quality from traffic is a serious issue. But parking them is a perennial problem. Giken’s solution, an anti-seismic parking system, takes the bikes underground and out of the way, with only a deposit system at the surface.

Under the ground is a cylindrical silo some 11m deep and 8m  across that holds a racking system, arranged radially around a central mechanism that incorporates a lift system and a robotic placing machine that whisks bikes from the street-level kiosk (it’s this that is 7m wide; the kiosk doesn’t cover the whole area of the shaft throat).

Each user’s bike is equipped with an ID tag attached to its front  forks, with owners holding a matching smartcard. To use the system, the bike’s front wheel is pushed into a slot on the surface kiosk; the placing mechanism grabs onto it, whisks it down into the silo and files it into one of the radial slots. To retrieve the bike, the owner holds the card up to a panel on the kiosk; the mechanism then works in reverse, locating the filed bike and bringing it back to street level; this takes an average of 13 seconds. The store can hold mountain bikes, electric bikes and bikes with front baskets or rear child seats.

”Imagine how much area would be needed on the surface for a bike park to hold 144 bicycles

Haan Admiraal, ITACUS, ITA-AITES

“It’s a formidable space-saving technique – imagine how much area would be needed on the surface for a bike park to hold 144 bicycles,” said Haan Admiraal, chair of the underground space committee (ITACUS) of international tunnelling and underground space association ITA-AITES at a recent seminar on underground engineering at the Institution of Civil Engineers in London. It is built with a proprietary system developed by Giken that uses interlinking piles, pressed into the ground hydraulically to form the walls of the silo; the void is then excavated up to this wall. This is a low-noise, vibration-free, seismically safe system that causes minimal disruption to neighbours when installed, developed for the crowded, earthquake-prone region, and is also used for other types of construction.

For some applications, underground may just be the best environment. ITACUS vice-chair Antonia Comaro gave the examples of museums and art galleries. “Architects and engineers spend an inordinate amount of effort, time and money to design iconic, beautiful buildings, and quite rightly,” she said. “But then they have to spend even more effort and money to devise ways to protect the priceless artworks they are to hold from sunlight and changes in the environment. The Paris Louvre had the idea to put its lobby underground, with the famous glass pyramid as its entrance; but it might well be that below ground would be the best place for the entire institution, and other galleries where light- and moisture-sensitive objects are going to be on display. You are starting from a default position of no light – the effort is spent on bringing it in and controlling it, not keeping it out – and the insulating effects of soil  and rock help keep the environment very stable.”

”It might well be that below ground would be the best place museums, and other galleries where light- and moisture-sensitive objects are going to be on display

Antonia Comaro, ITACUS

This is one of the rationales behind one of the world’s most intriguing plans for a large building: the Earthscraper, which has been designed  for a specific location in Mexico City by architecture practice BNKER Arquitectura (pleasingly, the company name in English is said as  ‘Bunker Architecture’). Best described as an underground skyscraper,  the Earthscraper has museum space as an integral part of its concept. This is partly owing to its location.

Originally devised as an entry for an architecture competition, Earthscaper is designed for the city’s largest public square – and,  indeed, one of the world’s largest – the Plaza de la Constitucion, known as Zocalo. Bordered by the city’s cathedral, the National Palace and the city government buildings, Zocalo is a square 240m on each side, giving it a total area of 57,600m². It is a ceremonial space with a flagpole at its centre that is raised every morning and lowered every night, and is a significant area in Mexico City’s public life.

Which makes it slightly incongruous that the plan for the Earthscraper involves digging it up; especially as Mexico City has a long history, being the site of Tenochtitlan, the capital of the Mexica and Aztec civilisations, and a correspondingly rich archaeological record, parts of which would be showed off in the structure’s museum space. However, the land pressure on the city is extreme. “New infrastructure, office, retail and living space is required but no empty plots are available,” said BNKR founder and chief executive officer Esteban Suarez. “Federal and local laws prohibit demolishing historic buildings and, even if this was so, height regulations limit new structures to eight stories. So we have a massive programme of hundreds of thousands of square meters and nowhere to put it. This means the only way to go is down.”

Earthscraper is designed to be “the antagonist of the skyscraper”. It is an inverted pyramid 300m deep – as deep as the Shard in London is high – whose base would occupy almost the entire area of Zolcalo apart from the roads around the edge. The base would be covered with  a thick glass sheet to allow Zocalo to still  be utilised for its current uses, while still allowing light to penetrate into the void at the centre of the structure, which will act like an enormous lightwell for the structures arranged around the walls of the pyramid.

The pyramidal form is not coincidental. If it were housed in a simple vertical shaft, the walls would tend to cave in and would need enormous supporting structures to prevent  a catastrophic collapse. Sloping the walls inwards on all sides means they are more self-supporting, Suarez explained. It’s also  a matter of concern that Mexico City is in  an active earthquake zone, but again the pyramid is a logical choice. “Because its structure must already resist the lateral forces of the surrounding earth, it would  be especially strong against the lateral forces of an earthquake,” Suarez said.

With the ‘buildings’ sections of the Earthscraper lining the walls of the pit, natural light can penetrate down into its depths, although the plans include a fibre-optic system to illuminate the deepest levels; vents in the top sheet would also allow natural ventilation. “We hope that in creating a pleasant environment underground we would convince sceptics of the viability of our scheme,” Suarez said.

The floors nearest the surface would be museum space, with retail developments below that, then residential, and office space at the bottom. The top glass plate – which we hope will be frosted in some way or only the boldest would walk across it – would be able to host anything from Christmas skating rinks to major artistic performances, religious gatherings and political protests. “It preserves the iconic presence of the city square and the existing hierarchy of the buildings that surround it,” said Suarez.

In engineering terms, one of the biggest challenges would be water. The lowest 165m of the pit would be below Mexico City’s water table, and therefore effectively floating on mud. This would necessitate a “greater investment in structure” than a skyscraper, making it about  30 per cent more expensive. The cost would require government intervention, with tax breaks for developers similar to those that helped finance the new buildings on London’s Isle of Dogs.

For the moment, however, the Earthscraper remains an intriguing  and ingenious concept, a potential space to be watched. For real underground activity, a city much further north shows a way forward.

One of the biggest stumbling blocks with building underground is what’s already there. Whether it’s the basements of buildings, sewerage systems, electrical infrastructure or existing tunnels for roads, subways and underground railways, cities without an underground hinterland of some sort are rare. “You need to have accurate and reliable surveys of  the existing situation,” said Martin Knights, senior vice-president for earth engineering at contractor CH2MHill, “and some sort of overarching plan of what else you want to fit in and how it’s supposed to be used.”

Leading the way in this respect is the Finnish capital of Helsinki, where the local population love outdoor life but, for most of the year, can’t indulge in it without risking frostbite. The city has an underground masterplan that governs all of its subterranean activities, which are extensive: underneath its central park can be found  a 100-yard-long lake that can hold nine million gallons (41 million litres) of icy Baltic water, which is used to cool the city in the summer (when temperatures can reach 30°C). Conversely, the city also has a huge underground heat pump system, which recovers thermal energy from wastewater and diverts it into domestic district heating.

Elsewhere under the city is a running circuit, an ice-hockey hall, the Itäkeskus swimming pool, the Temppeliaukio Church and a shopping centre. A series of light wells dotted around the surface light up the subterranean spaces, whose volume adds up to some nine million cubic metres, with 400 separate facilities linked by tunnels, and the master plan has another 100 locations earmarked for future resources. There are also plans for an 80km undersea tunnel linking Oulo in northern Finland with Helsinki, to create an economic ‘twin town’.

But in many cities, the main reason to go underground is the same as it has been for more than a century: to get roads off the surface, relieve congestion and open up surface ground for new uses. One example is Boston, Massachusetts, where a project known as Central Artery Tunnel or the  ‘Big Dig’ took an elevated highway that  was considered a blight to the city below ground and constructed a new tunnel  under the harbour. Further west, Seattle, Washington, is attempting to bury an the Alaskan Way overpass, which is old and decaying. This is not going well, with the tunnel boring machine stuck 10 per cent of the way through a 1.7-mile dig for more than a year.

In the UK, meanwhile, two major tunnelling projects could transform west and south London beyond recognition. CH2MHill is involved  with feasibility studies to turn the Hammersmith Flyover into a tunnel. Another study is looking at the possibility of burying the South Circular Road. In a £30bn project that includes a tunnel on the North Circular at Brent Cross aimed at improving facilities for cyclists and pedestrians at ground level while also improving air quality as London’s population and therefore its traffic continue to increase.