What is the Meaning & Definition of tunnel

We understand by tunnel to the construction that has by objective communicate two extremes which, otherwise, would be kept separate. The tunnel allows thereby passing through enclosed spaces that are usually underground. One of the main features of all tunnel is that they have a roof and is unique ventilation which is maintained in both points, there being no possibility of leakage or crossing it out of those two points of communication.
The tunnels are mostly artificial constructs that human designs and executes with the sole purpose of moving from one side to another when two points are closed or covered matter. There are two types of spaces that are often constructed tunnels: the natural areas (mountains, hills, canyons) in which is possible to tunnel both for the passage of human beings and for the passage of water, energy or materials of various kinds; and urban spaces in existing tunnels under the ground serve to boost public transport (either in the case of the subways or tunnels for regular vehicles).
The investment of time, capital and human force for the construction of tunnels is often very important since the tunnels are some of the more complex constructions that human beings can do (to be completely artificial and therefore require certain security features). In general, tunnels are made via blasting or explosion of the spaces to empty, by drilling and excavation. According to the type of tunnel that you want to build there will be different methods most useful for obtaining specific results. In some cases tunnels can be abandoned, especially when they are built with goals specific and timely, as it is the case of the extraction of natural resources.
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