Tunnel Engineering Construction
Underpass is built underground or underwater or in the mountains, laying railways or building roads for motor vehicles. According to its location, it can be divided into mountain tunnel, underwater tunnel and urban tunnel. In order to shorten the distance and prevent the ramp from crossing under the mountains or hills, it is called mountain tunnel; in order to cross the river or channel, it is called underwater tunnel; in order to get used to the demand of railway passing through big cities, it is called urban tunnel. Among the three types of tunnels, the mountain tunnel has the most buildings. Including tunnel route selection, vertical section planning, cross section planning, auxiliary tunnel planning, etc.
Route selection: the location and length of Underpass shall be selected according to the route standard, terrain, geology and other conditions. Multiple schemes should be compared for route selection. Auxiliary tunnel and operation ventilation should be considered for long tunnel. The location of the portal should be selected according to the geological conditions. Consider the stability of slope and head slope to prevent collapse.
Vertical section planning: the longitudinal gradient along the middle line of the tunnel shall be subject to the constraint gradient of the line planning. Because of the high humidity in the tunnel, the adhesion coefficient between the wheel and rail decreases, and the air resistance of the train increases, so the longitudinal gradient in the longer tunnel should be reduced. The shape of longitudinal slope is mainly single slope and herringbone slope. Single slope is conducive to elevation, while herringbone slope is convenient for construction drainage and mucking. In order to facilitate drainage, the minimum longitudinal slope is generally 2 ‰ - 3 ‰.