How to build an ＂underground city＂, deep space research has an answer.
People in The Wandering Earth live in underground "underground cities". In the future, "underground cities" will not only exist in science fiction films. Scientists are currently conducting deep space research to explore how to build "underground cities". Recently, the reporter interviewed Xie Heping, an academician of China Academy of Engineering and dean of Shenzhen University’s Institute of Deep Earth Science and Green Energy, and asked him to describe the future survival of underground space from a scientific perspective.
"Underground City" is a world-class frontier scientific research.
"The development and utilization of deep space is not just science fiction, but a scientific research project that is being studied all over the world, and it is a frontier scientific research topic in the world." Xie Heping said that the comprehensive utilization of underground space has attracted great attention internationally, and many international organizations have been studying the utilization of underground space. These international organizations include the International Association for Tunnels and Underground Space (ITA) established in 1974, the International Joint Research Center for Underground Space (ACUUS) established in 1996, and the International Trenchless Technology Association (ISTT) established in 1986. The Tokyo Declaration, adopted by the International Conference on Urban Underground Space in 1991, also emphasized that "the 21st century will be the century of human exploitation and utilization of underground space", and predicted that one third of people will live in underground space in the future.
According to Xie Heping, there are many cases of scientific development and utilization of underground space in the world. For example, an underground park has been built in Finland, which will turn the space 120 meters underground into an oxygen bar with salty and humid air. The constant temperature is 11℃~12℃ all year round, and there are almost no allergens and bacteria, which can recuperate patients suffering from respiratory tract, tuberculosis and other diseases. The mine playground in North Wales, England, which was built in 2014, is 150 meters underground and has the world’s largest underground trampoline in a thermal insulation and moisturizing environment.
Many countries are also trying to develop underground space. For example, Singapore plans to build an underground science and technology city, which is equivalent to 30 floors underground in the Western Science Park, to be used by biomedical industry and life sciences, and to accommodate new population in the future.
"The total area of a city is not only the ground area, but the total utilization space of a city should be multiplied by 40% of the development depth. These underground spaces have unique advantages such as constant temperature and humidity, sound insulation and isolation, natural resistance to natural disasters, low background radiation and clean environment. " Xie Heping said that using the advantages of these underground spaces can carry out underground medical research and treatment, such as Hodgkin Cave in Uzbekistan, which can improve the cellular immunity of patients with chronic obstructive pulmonary disease; Related scientific research activities can also be carried out. For example, the Large Hadron Collider in Europe is 92 meters underground. "If more exploration and utilization are carried out, it is possible to make deep space a better way of human migration than space settlement and coping with future earth disasters in the future." Xie Heping said.
How to build a future "underground city"
How to build an underground city in the future? Xie Heping introduced his academic article published in Journal of Coal Industry recently, and put forward his strategic conception and scientific research demonstration on the construction of version 5.0 of "Underground City". According to this idea, 0~50 meters underground is underground rail transit, pipe network system and refuge facilities, 50~100 meters underground is underground livable city, 100~500 meters underground is underground agriculture, underground medicine and underground ecological circle and strategic resource reserve, and 500~2000 meters underground is underground energy circulation belt, underground pumped storage, compressed air power station, underground thermal energy and other storage and utilization, and more than 2000 meters underground is underground.
"Regarding the development and utilization of deep space, I put forward the concept of five eras, including the 1.0 era of passive underground space utilization, the 2.0 era of scientific development of underground space and underground ecological city, the 3.0 era of deep ecological circle construction, the 4.0 era of deep scientific laboratory and deep space capsule, and the 5.0 era of liquid mining of deep solid resources." Xie Heping said.
The 1.0 era of deep development is to build air-raid shelters, warehouses, subways, underground shopping malls, underground parking lots, etc. In the 2.0 era, there will be a complete and livable eco-city, with sunshine, self-circulating water pumps and intelligent air regeneration systems. In the 3.0 era, there will be ecological and environmental underground space utilization, and the environment of underground ecological circle will be constructed, including artificial sunshine, ecological vegetation, deep farming and animal husbandry, water and ecological self-circulation system, etc. In the era of 4.0, in-situ scientific experiments with different depths should be carried out, and theoretical systems of deep physics, biology, medicine and rock mechanics should be constructed to lay a theoretical foundation for human beings to March into the deep part of the earth.
In the 5.0 era, it is necessary to invent shield mining, separation, charging, gasification and power generation integrated technology and equipment to directly transform solid resources into liquid, gas and electric energy. By that time, underground roadway mining will be patrolled, inspected and operated by drones and robots. Using the energy generated by coal powder explosion and gas explosion, in-situ power generation will be carried out at a depth of 3,000m underground, and the electricity, hydrogen and liquefied carbon will be transported to the ground instead of solid resources, and a self-circulation development and utilization system with deep in-situ ecological green and low carbon will be built. "At present, the doctoral team led by me is doing pre-research in this area." Xie Heping said.
Step into the era of "Dungeon" 2.0
According to Xie Heping, the earth’s solid mineral resources can be buried more than 40 kilometers, and 70% of China’s proven iron ore, copper ore and bauxite resources are below 2 kilometers. Take geothermal resources as an example, there is 125.4 billion thermal energy in the outermost 10 kilometers of the earth’s crust, which is equivalent to 2000 times of the total thermal energy of coal produced in the world.
At present, China has listed deep-seated development as a major national science and technology project, and it is necessary to comprehensively improve the level and ability of deep-seated engineering science and technology, and strive to reach 15,000 meters by 2035; Oil and gas exploitation should reach 10000 meters; Geothermal development to 6000 meters, solid resources mining to 3000 meters, underground space engineering to 1000 meters.
"At present, the utilization rate of underground space in the world is about 30%, while in our country it is only 17%." Xie Heping said that with the development of China’s deep development strategy, how to rationally develop and utilize these underground spaces is "a major national strategic scientific research project that needs pre-research first".
"Taking coal mines as an example, the existing underground space of coal mines in China is about 13.9 billion cubic meters, and it is expected to reach 24.1 billion cubic meters by 2030, with a length of about 1.6 million kilometers, which can circle the equator 40 times. How to use such a huge underground roadway space? " Xie Heping said that the transformation and utilization of waste gas mines in foreign countries have many uses and forms. For example, using geothermal energy to develop underground agriculture, scholars at Nottingham University are considering using geothermal energy naturally existing in mines to transform 150,000 abandoned coal mines into underground farms.
"We must know that the underground itself is warm in winter and cool in summer, and the construction cost of underground greenhouse is only 1/4 of that of ground greenhouse agriculture." Xie Heping said that in 2017, an underground farm was built in London, England, using an air-raid shelter 33 meters underground. With LED lights as the light source, hydroponics technology can save 70% of water, no pesticides are needed at all, and plant growth is not affected by seasons and weather. It can be harvested in 6 to 28 days, and the underground agricultural product brand has been successfully launched.
"There are also ways to build a small intelligent underground parking garage, underground pumped storage power generation, compressed air storage power generation station, etc., which can be tried in the utilization of underground space." Xie Heping said that underground sewage treatment plants can also be built. For example, Hong Kong plans to put all surface sewage treatment underground; You can also build underground hotels, carry out landscape tours and underground in-situ laboratories. For example, the dark matter laboratory in South Korea is 700 meters below the mine.
In the aspect of deep space utilization, China has also begun some explorations. At present, the first phase reconstruction project of the five major coal mines in the west of Beijing has been started. Xie Heping said that according to the plan, the ground is green mountains and green waters scenic area, college education and training area, tourist resort area, sports and leisure area and high-tech park, and the underground will be developed into underground coal mine safety production training practice area, underground ecological landscape experience area, underground agricultural planting area and deep scientific exploration area. "We hope to turn it into a national demonstration area for the development and utilization of coal mines, a headquarters for scientific research and development and an experimental base for underground space research and development." Xie Heping said. In his view, regarding the construction of "underground cities", "it has just entered the 2.0 era, and it may take decades or even hundreds of years to reach the 5.0 era, but we can imagine the future trends and bright prospects."
(Reporter Zhan Yuan)