We understand by tunnel that construction whose main objective is to communicate two ends that, otherwise, would remain separated. The tunnel thus allows passage through closed spaces that are generally underground. One of the main characteristics of all tunnels is that they have a roof and that the only ventilation is the one that is maintained at both points, there being no possibility of exiting or crossing it outside of these two points of communication.
Tunnels are mostly artificial constructions that human beings design and execute with the sole purpose of passing from one side to the other when two points are closed or covered with matter. There are two types of spaces in which tunnels are usually built: natural spaces (mountains, hills, canyons) in which the tunnel can be made both for the passage of human beings and for the passage of water, energy or materials of various kinds; and the urban spaces in which underground tunnels serve to energize public transport (whether in the case of subways or tunnels for regular vehicles).
The investment of time, capital and human force for the construction of tunnels is usually very important since tunnels are some of the most complex constructions that can be carried out by the human being (being completely artificial and therefore requiring certain security features). In general, the tunnels are made by blasting or exploding the spaces to be emptied, by drilling and by excavation. Depending on the type of tunnel that you want to build, there will be different methods that are more useful for obtaining specific results. In some cases, tunnels can be abandoned, especially when they are built for specific and specific purposes, such as the extraction of natural resources.
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