Why is the subsea tunnel dug so deep that it won't be submerged by seawater? How did you do it?

Our infrastructure capacity and technical level in China are the highest in the world. Over the years, China has built many super projects, such as the Three Gorges Dam, the South-to-North Water Transfer Project, the Hong Kong-Zhuhai-Macao Bridge and so on. These super projects all represent the highest level of construction in China to some extent. Among many engineering construction projects, the construction of subsea tunnel is considered to be the most difficult, because subsea tunnel not only has to overcome the resistance of seawater, but also has to build a fully enclosed tunnel on the seabed. The construction is very difficult. At present, only three subsea tunnels have been opened to traffic in China, namely Xiamen Xiang 'an Tunnel, Qingdao Jiaozhou Bay Tunnel and Hong Kong-Zhuhai-Macao Bridge Tunnel. This shows how difficult it is to build a cross-harbour tunnel. Many friends have a question about this. Why is the cross-harbour tunnel dug so deep in the sea, but the interior will not be submerged by seawater, let alone leak water? How is this done? Let's take a look together.

Engineers have been exploring and studying the construction of subsea tunnels. At present, three subsea tunnels in China are mainly constructed by drilling and blasting method and immersed tube method. Let's talk about the drilling and blasting method, which is a more traditional tunnel excavation method. This tunnel construction method is not in direct contact with seawater, but in the rock layer below the seabed. Engineers first plan the route of the cross-harbour tunnel. Then calculate the explosive quantity and blasting point before blasting. After blasting, clean up debris such as gravel, and then dig through the tunnel bit by bit with a machine. Both Xiang 'an Tunnel in Xiamen and Jiaozhou Bay subsea tunnel in Qingdao use this method to build tunnels. However, this method has strong limitations and high geological requirements on the seabed, so it cannot be applied to all the construction methods of submarine tunnels. What if it is a sea with soft rocks and flat terrain?

Generally speaking, the immersed tube method will be used in this case. This method is to put the immersed tube designed and manufactured in advance directly into the designated water area, and finally connect the tunnels by splicing. Seeing this, many people may ask, won't this method be submerged by seawater? The answer is of course no. The joints between immersed tubes are generally fixed with concrete, and the air tightness between immersed tubes is very high, so the subsea tunnel will not leak water or be submerged by seawater. The submarine tunnel of Hong Kong-Zhuhai-Macao Bridge was designed and constructed by immersed tube method. It can resist natural disasters such as earthquakes and tsunamis, and the seismic grade has reached level 7, so there is no problem in safety, and there is no need to worry about flooding inside the subsea tunnel.

Finally, the headmaster concluded that the construction of the cross-harbour tunnel emphasizes safety. At present, the main tunnel construction methods in China are drilling and blasting method and immersed tube method, which can ensure the safety of the tunnel to the greatest extent and ensure that the tunnel will not be submerged by seawater. After all, if the cross-harbour tunnel collapses or leaks water, the consequences will be very serious, so the construction of the cross-harbour tunnel is very rigorous, and we should praise the wisdom of the engineers.