What method is used for seabed piling?

There are many piling construction methods, such as hammering method, vibration method and buried pressure method. Vibration method is widely used in China, that is, vibration pile driver is used to pile, and measures such as water injection and mud suction are used to assist the sinking of hollow circular piles inside and outside the pipe wall. Burying method is to drill or dig holes first, and then bury piles.

Cast-in-place pile is also called bored pile or dug pile. The basic construction method of cast-in-place pile is to drill or dig holes first, then put down the reinforcing cage and pour concrete. This method has the advantages of fast construction speed, low labor cost and simple equipment. 1965, a bored pile with a pile diameter of 1 m was first used in the construction of a bridge in chengdu-kunming railway. Since then, bored piles have been widely used in railway bridge construction in China.

Third, the pipe string

The hollow circular pile with larger diameter is called pipe pile, and the pile foundation built with pipe pile is also called pipe pile foundation. Pipe string foundation is generally suitable for bridge site conditions such as water depth, no overburden, overburden thickness and rock surface fluctuation. The pipe string can pass through various soil cover layers or caves and be supported on the surface of dense soil or fresh rock. Generally, prestressed concrete pipe columns or steel pipe columns are used.

The Wuhan Yangtze River Bridge in China, which was built at 1957, adopted the pipe pile foundation with the diameter of 1.55m for the first time. The pipe string sinks to the foundation rock stratum through the overburden, then the rock in the pipe string is drilled to the required depth with a large rig, then the steel skeleton is placed, underwater concrete is poured, and the pipe string is anchored in the rock wall. In the early 1960s, the Nanjing Yangtze River Bridge in China adopted a large prestressed concrete pipe pile foundation with a diameter of 3.6 meters. The pipe pile foundation can reach the depth of underwater construction that pneumatic caisson can't reach, which can avoid working under water and high air pressure, is beneficial to the health of workers, and can be constructed all year round without being affected by flood season. Therefore, pipe string foundation is widely used. The diameter of the pipe string is also increasing. For example, the diameter of the pipe string used in Ganjiang Bridge in Nanchang, China is 5.8 meters. ..

Four, open caisson foundation

Bridge foundation constructed by open caisson or pneumatic caisson (Figure 2 caisson foundation). This foundation is used less now. Because of its good integrity, high stiffness and reliable force transmission, it is still used for bridge repair in long-span and deep-water areas.

The open caisson is a vertical shaft, and the lower end of the lowest section is provided with a steel or reinforced concrete blade foot. Its plane shape can be made into rectangle, circle, round end, etc. According to the shape of pier and abutment, add a partition wall in the middle to make it double-hole or porous. Building materials can be wood, steel, concrete, reinforced concrete, etc. Open caissons can be built on piers in shallow water, prefabricated on shore in deep water, and then transported to piers by floating. The construction procedure of open caisson foundation is generally to dig in the hole wall, and the shaft will gradually sink by self-weight or pressurization. One shaft will quickly sink into the soil, then another shaft until the last shaft sinks into the design elevation. Then clean up the soil at the bottom of the well, pour a layer of underwater concrete to seal the bottom of the well, then pump water and fill it with concrete or sand, or make a hollow caisson. Finally, a reinforced concrete cover plate is poured on it, and a pier is built on it. In the construction process, in order to reduce the friction between the shaft wall and the soil when the shaft sinks, steel pipes can be embedded in the shaft wall and pressurized with high-pressure water, mud or high-pressure airflow to assist the sinking. 1936, the caisson foundation of the anchorage pier of the Oakland Bay Suspension Bridge in San Francisco, which was built in the United States, was sunk with a circular cover caisson for the first time, with a plane size of 60×28 meters and 55 shafts. This kind of open caisson foundation is also applied to Nanjing Yangtze River Bridge and Zhicheng Yangtze River Bridge in China. The sinking depth of the open caisson of Nanjing Yangtze River Bridge is 54.87 meters. The rock surface elevation difference at the pier of Zhicheng Yangtze River is 3.7 meters. In the design, the traditional vertical plane method is broken, and the high and low blade feet are made according to the slope of the rock surface, so that the bottom surface of the open caisson is consistent with the rock surface.

Pneumatic caisson is a bottomless box structure with a double-door corridor at the top for people and materials to enter. After the caisson sinks to the bottom, inject compressed air to prevent water from entering. People dig the foundation inside, so that the caisson will continue to sink to the design elevation. During the construction of pneumatic caisson foundation, it can deal with sinking obstacles without pouring underwater concrete, and can directly observe the foundation prototype with reliable quality. But construction workers need to work in high-pressure air, which is not only inefficient, but also harmful to health. Bridges built in China in the early days, such as Qiantang River Bridge, adopted this technology.