Underground cities are part of the cities of the future. People according to the depth of the ground below the ground is divided into five layers: the surface layer, 5 meters deep; ground shallow layer, 10 meters deep; ground middle layer, 30 meters deep; ground deep layer, 100 meters deep; ultra-deep layer, 100 meters deep or less. The surface layer, the shallow layer and the middle layer of the earth have been widely developed and utilized, such as underground streets, underground railroads, underground power stations, underground grain depots, underground radioactive waste disposal sites and so on. People are turning their attention to the deep and ultra-deep layers of the earth.
The advantages of underground cities are constant temperature, heat insulation, sealing, quiet, not subject to climate and other natural conditions, better than the ground building can prevent possible disasters and reduce earthquake damage. If there is already a city above ground and an underground city is developed at the same time, the space of the city will be greatly expanded and the congestion on the ground will be relieved.
Currently, the world's underground city is mainly a supporting network connected by the subway, which basically belongs to the category of transportation. Urban designers in European countries car turn their attention to the underground. The undersea tunnel that crosses the English Channel and connects Britain and France has been built and is in operation. Spain and Morocco are discussing the construction of a submarine tunnel in the Strait of Gibraltar to connect the two countries. Germany and Denmark are negotiating the construction of a railroad tunnel linking the two countries in the Fehmarn Strait. Swiss engineers study the feasibility of building a major city under the Alps.
The island nation of Japan, in an effort to gain more living space, has earlier proposed building underground cities. Japan's Ministry of International Trade and Industry (MITI) has formulated a "large-depth underground space development technology" to dig a 300,000-cubic-meter hole in the ground and build an underground city with office buildings, concert halls, stadiums and other facilities there, with large section tunnels connecting the various subterranean cities, and levitation trains and unmanned underground airplanes to transport people and things.
The Japanese government and some major construction companies are preparing to build a small underground city by 2020. Japan's Tomita Corporation has drawn up plans for the underground city. Located 200 meters deep underground, this underground city would be built with 200-meter-diameter pipes in the shape of a hexagon, and would use computers and other high-tech means to reproduce the natural environment on the surface: the change of day and night, the change of seasons, and the rain, sun, and snow.
In 1994, Japan in the sea level of 40 meters below, the construction of three large underground oil storage tanks; they also have 17 in the planning of the larger underground transportation projects, including a cost of $ 12 billion across the Tokyo Bay Expressway; Japan's Shinjuku has been built in a thousand huge underground city, underground housing dotted with underground transportation in all directions, there are according to the Renaissance There are Italian castles built in the Renaissance architectural style, forest parks with lush flowers and trees and birds singing, shopping centers with a wide range of goods, and wide and luxurious underground plazas.
However, the construction of an underground city requires enormous human, material and financial resources, and its cost is difficult to estimate accurately in advance. In addition, the underground city of air freshness, groundwater seepage, long-term underground life on people's psychological and physiological impact, etc., but also need scientists and engineers to carry out in-depth research and study.