 |  |  |  | Land Use & Location | Isolation & Opacity | Preservation & Protection | Topographic reasons | 
The reasons to go underground for environmental purposes are of different types. They can be for | - Land Use & location, that means mainly lack of surface place which is now the case not only in mega cities but in nearly all town and cities around the world.
| | - Isolation & Opacity : the ground is massive and opaque and provides a variety of advantages in terms of isolation, such as climate, natural disasters and earthquake, protection, containment. Isolation is an important reason for placing facilities underground.
| | - Environmental preservation : the ground also provides a variety of advantages in terms of protection of the environment, such as aesthetics or ecology. These are notably important aspects in designing facilities with a low environment impact.
| | - Topographic reasons : In hilly or mountainous areas, the use of tunnels improves or make feasible various tranport options uch as roads, railways, canals, etc.
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