The twentieth century was a century of skyscrapers, and the world cities were expanding more and more upwards due to the necessities of urbanization. But in the 21st century, there is a new tendency to go underground. Cities seem to be expanding for commercial, industrial and underground transportation purposes.
The global urbanization process has created many common problems in many cities around the world. The increase in population naturally leads to an increase in demand for reliable infrastructure, which should be accompanied by an increase in energy efficiency in urban living and also an increase in public awareness about environmental protection. The use of sub-surface spaces helps cities to respond to these ever-increasing demands, while the urban landscape is well preserved.
According to United Nations statistics, by the year 2050, seventy percent of the world’s population, that is, about seven billion people will live in cities, and the rural population will decrease and at best remain constant. This change in population distribution in the future will meet new needs in terms of continuous improvement of sustainable and efficient urban development, such as reliable transportation, water distribution and urban sewage services, environmental sustainability, expansion of green spaces and recreation areas, optimization And reduction of energy consumption and so forth. Delivering these demands presents many challenges to city managers. Because the space required to create new facilities or to improve the present situation is often unavailable.
Another area where urban managers are accused of using underground space is the severe climate change. For example, a city like New York has experienced extreme storms in recent years, and according to experts, this is becoming a normal practice for the city. In such cases, the city’s economic life and the safety of people are more protected in sub-surface areas. Also, in cities like Beijing and Hong Kong, with high levels of air pollution, the use of structures and underground roads is in the agenda of urban executives to protect citizens’ health.
In most cases, the use of underground spaces to solve urban constraints is seen as a second hand option by many urban planners and managers due to its rigorous access and cost that goes far beyond the realities of a modern city. In cities that are currently developing, there is no longer such a look at the issue because modern city designers look at underground spaces as an opportunity and address the problems, e.g. lack of financial resources by attracting investment.
In many cases, the use of solutions for urban problems based on underground spaces is the only available solution. Also, if in the early stages of planning and starting a project, the use of subsurface space capacity is mentioned as an option that is aligned with other options and not as the last possible way for designers, undoubtedly, we could hope for a change in the settlement of urban problems.
It should be noted that the use of underground spaces is not limited to infrastructure projects; it can rather be used for commercial, residential, storage, transportation and treatment purposes and preservation of historic heritage in a way that provides better urban development.
Using underground cities has a long history. From ancient times to the Cold War, people have used such shelters to protect their lives and property. Here are some examples of underground cities from past to present:
۱- Underground Derinkuyu city in Turkey. The city was built in seven underground floors with twenty thousand inhabitants. In this ancient city, there was a shop, a church, and even a school. It is said that Christians have lived in this city, who were fleeing from the Roman Empire.
۲- Underground Kariz Town in Kish Island. The city was more than 2500 years old and was originally used to manage freshwater for inhabitants of the island.
۳- The underground city of Beijing was built on command of Mao for 10 years. The purpose of the construction of this underground city, which contains 30 kilometers of tunnels and is built on an area of 85 square kilometers, was to protect people’s safety in aerial bombardments. There were many facilities in this city such as school, shop, theater and even a skating track.
۴- During World War II, a secret underground facility called Burlington was created to protect the British men from nuclear attacks. The facility had a train station, hospital, artificial lake and even a BBC studio with a capacity of forty thousand people.
۵- The city of Helsinki, the capital of Finland, has begun to build an underground network since 2011 in an effort to cope with the cold weather. According to a comprehensive plan, more than 400 buildings and urban spaces are to be built at a depth of 30 meters from the ground. In this plan, the underground trails connect the main city hotspots. The ultimate goal is to have space on the ground for real estate and accommodation, while industrial facilities act in the underground.
۶- In Montreal, Canada, an underground network with more than 32 kilometers of tunnels in an area of 12 square kilometers has been built. There are 60 commercial centers, hotels, banks, offices, museums, concert halls, academic spaces, seven subway stations and 12 external access points in the sub-space, which employs more than 500,000 citizens a day.