Yangtze River shipping has special regulations on bridge spacing. If it is less than this spacing, it will affect the safety of Yangtze River shipping. In addition, from the perspective of landscape, too dense bridges hinder the visual landscape.
From a practical point of view, the length of the bridge approach on both sides should be considered when building a bridge, so the demolition of the bridge should be considered, and the demolition of the tunnel is much smaller. Demolition in China is often a non-technical problem in engineering construction. Take Wuhan Yangtze River Tunnel as an example. Hankou entrance is a five-nation concession, which is a cultural relic protection building. There is no room for building an approach bridge.
Judging from the use situation, the use environment of tunnel is better than that of bridge. Because the tunnel is embedded in the rock stratum as a whole, it is less affected; No matter what bridge form is inseparable from the pier, it is greatly disturbed by the external environment, such as strong winds and floods.
From the perspective of process cost, the tunnel is obviously higher than the bridge. Tunnels are mostly excavated by immersed tube or shield method, which often goes deep into underwater rock strata, with a large amount of earthwork and complicated construction environment. Bridges are mainly steel structures, which are much cheaper than geotechnical techniques.
Extended data
Wuhan Yangtze River Railway Tunnel is another river-crossing passage in Wuhan. As the name implies, it is a river-crossing passage for highways and subways. The total length of the tunnel is 4.66 kilometers, and the segment diameter is 15.2 meters, which is more than six times that of Metro Line 2. It is the largest tunnel under the river in China at present.
The tunnel is divided into three layers: the upper layer is the flue of the highway tunnel; The middle layer is a one-way three-lane expressway lane; The lower floor is the section of Metro Line 7, as well as the escape route, cable corridor and subway smoke outlet.
Wuhan Yangtze River Railway Tunnel has a main entrance and exit on Macau Road, just below Sanyang Road Interchange. Walking into the tunnel, you can see that it is wider than the previous Yangtze River Tunnel, and there are three lanes in one direction.
The speed limit of the tunnel is 60 kilometers per hour, and there is no dotted line lane change on the ground. In the tunnel, there is an evacuation staircase every 75 meters. Once a dangerous situation occurs in the tunnel, you can directly enter the escape route by pulling open the stair cover. From the escape route, citizens can go to Wuchang and Hankou, and evacuation lights indicate the direction.
The distance from the middle of the tunnel to both sides is about 1 km. You can reach the ground through the stairs, and it takes about seven or eight minutes to really walk. There is an emergency telephone every 200 meters in the tunnel. In case of danger, citizens can contact the staff of the public railway tunnel directly through this phone.
More than 200 cameras are installed in the tunnel, which can monitor the situation in the tunnel in real time through the big screen of the public railway tunnel operation center.
There is a smoke detection system in the public railway tunnel. Once the detector detects smoke, it will trigger the FAS fire alarm and the foam spraying system will start to put out the fire. At the same time, the smoke exhaust system will also play a role in eliminating smoke in the tunnel.
References:
Baidu Encyclopedia-Wuhan River Crossing Tunnel