Tunnel refers to the channel excavated in the existing building or earth and stone structure for three-dimensional transportation, mountain crossing, underground passage, cross-river, cross-sea, pipeline transportation, cable underground, water conservancy project, etc. The tunnels are not necessarily all underground tunnels, but only underground tunnels or underground roads. The main building consists of a hole and a cave door. The auxiliary equipment includes a car shelter, fire fighting facilities, emergency communications and drainage facilities. The long tunnel also has special ventilation and lighting equipment. Most of the functions of the tunnel are for pedestrians, bicycles (bicycles), general road traffic, motor vehicles, rail traffic, or canals, while some tunnels are only responsible for water, oil pipeline transportation or other specific services, including military and commercial logistics. Wait.