The longest sea-crossing bridge in the world is located in China, which is the Hong Kong-Zhuhai-Macao Bridge, with a total length of 55 kilometers. In order to facilitate the passage of ships, a 6.7-kilometer-long undersea tunnel extending between two artificial islands was specially built, which can be said to be a very humanized cross-sea bridge. Such a long bridge, in order to resist earthquakes and typhoons, was built with 400,000 tons of steel, enough to build 60 Eiffel Towers. However, to ensure the stability of the whole bridge, it is often supported by piers that go deep into the seabed, but some people wonder how the piers of the cross-sea bridge were built in such a deep sea. Does it float in the water?

In fact, piers can't float in the water. In order to ensure the stability of the cross-sea bridge, it is necessary to drive the pier into the seabed, mainly through three methods: one is cofferdam method; The second is caisson method; The third is piling. How do these methods work?

The first is the cofferdam method. The most troublesome thing in building offshore bridges is restless sea water. After determining the area where the pier needs to be built, the surrounding waters are surrounded by water-stopping structures such as steel sheet piles and earth-rock dams to form cofferdams, just like "wells", and then all the water in the middle is pumped dry by a pump, so that workers can start construction, build the pier and dismantle it after completion. It looks simple, but it actually takes a lot of time. If the sea area is deep, it is difficult to build several docks in ten and a half years, and this method will have an impact on the surrounding waters, so our country has not considered this method.

Cofferdam method can be used in shallow water, but what about deep water? In fact, the two caisson method can be used. The principle of this method is like putting a water cup upside down in the water and then draining all the water inside. The bottom of the sea is so deep, so how do you arrange it? This requires constant delivery of high-pressure air into the box. Because of the pressure, the water in the box will be squeezed out quickly. After sinking to the bottom of the sea, the workers began to dig at the studio at the bottom of the box, and then transported the soil out through a special device well, so that the caisson gradually sank, and the whole caisson sank while digging. After reaching the specified depth, the back cover will be sealed, and finally concrete will be injected to fill the whole studio, creating a perfect pier breaking the surface. This method was invented by Mao Yisheng, a native of China, and the pier of Qiantang River Bridge was built in this way. However, there is a very big disadvantage. Workers have to work in a high-pressure environment, which is harmful to human body and may even get "diving disease". If they get this disease, they may be completely paralyzed, so this method is rarely used so far.