Caisson is a box structure with a top and a bottom. There are blades at the lower end of the shaft wall, and there are partitions inside, which can float in the water. By adjusting the water in the box, the caisson can be controlled to sink or float. The top cover is equipped with an air lock, which is convenient for people, materials and soil to enter and leave the studio, while keeping the air pressure in the studio fixed. During construction, manual excavation will be carried out along the cylinder wall, and mechanical equipment or semi-mechanical equipment will abandon the soil outside the well, and blasting will be carried out when encountering boulders. As people dig in the middle, the caisson gradually sinks by its own gravity or external pressure, and sinks with the excavation, while continuing to pour new wellbore concrete on the water part. To put it simply, the workers took a huge barrel and put it on the sea. Then use the boat to pull the bucket to the designated piling sea surface. At this time, the workers are loading concrete into barrels with machines. When it is full, the bucket will begin to sink due to its own gravity. If the sinking depth does not reach the specified target, continue to inject concrete into the barrel until it sinks to the target position.
The piling method is to directly hit the seabed soil from the water. Generally speaking, you have to make a lot of columns in advance, and then the workers are driving those columns into the depths of the sea with a pile driver. According to the characteristics of different seabed strata, people can drive different kinds of piles. If the distance between the seabed surface and the solid bedrock is short, people will design short-end bearing piles, and the bedrock will provide the bearing capacity. If the solid bedrock is too deep, the pile will have to rely on friction to maintain its bearing capacity, so it is necessary to use long friction end bearing piles.
The above are two methods of fixing piers at sea. It's simple to say, and it needs a lot of technical and theoretical support, so the construction difficulty alone can be imagined. So the countries that can build a cross-sea bridge are really amazing, and China is one of them!