A long box shaped hydraulic structure built on the shore of a water area for repairing and shipbuilding is conventionally called a dock. The dock bottom is lower than the water surface, three sides are dock wall, connected with the shore, one side has dock mouth leading to water area, and has dock door. The dock was originally mainly used for repairing ships. With the development of large-scale ships, it is safer and more advantageous for ships of more than 100000 tons to be built in docks. Therefore, docks are also used for shipbuilding and are developing to large-scale.
The traditional method of building a dock is to build a cofferdam in the water near the bank, drain the water in the dam, and then excavate the foundation pit for dry construction. If the dock is built in the harbor basin, or the foundation is sandy soil with great permeability or rock foundation with river and sea cracks, or the cofferdam construction and removal is laborious, the cofferdam construction method is not suitable.
The dock is composed of dock chamber, dock head, dock gate, irrigation and drainage system and auxiliary equipment. When the ship is to be docked for repair, the water filling system shall be used to fill the dock chamber until the water surface is level with the water surface outside the dock. The dock door shall be opened to pull the ship into dock, and then the dock door shall be closed. The water in the dock chamber shall be discharged by the drainage system, and the ship shall be located on the pier seat on the dock floor.
For the ships repaired and newly built in the dock, water shall be poured into the dock chamber until the water surface is level with that outside the dock, and then the dock door shall be opened to pull the ship out of the dock.
Dock head and Dock Chamber dock head are water retaining structures separating dock chamber from water area, and dock door is set on it. Dock chamber is a space enclosed by dock head and dock wall, which is a place for repairing and shipbuilding.
The dock head and dock chamber are mostly reinforced concrete structures, which are divided into gravity type, anchorage type and decompression drainage type. The selection of structure and type is mainly based on the foundation conditions and considering how to deal with the buoyancy of groundwater acting on the dock floor. Each type has its own treatment method. Gravity dock uses the self weight of reinforced concrete dock to resist the buoyancy of water, which was used in previous docks.
Anchorage type dock is a kind of anchorage structure which is built in the good foundation under the dock bottom plate to resist the buoyancy of water. It is usually used in the soil with high friction resistance. Decompression and drainage dock is the use of drainage pipe system to drain the groundwater under the dock floor, and then eliminate or reduce the water buoyancy supporting force. It is generally used in cohesive soil with low permeability. As for sandy soil, because of its high permeability, groundwater can not be drained, this method is not suitable.
Because the size of the dock is becoming larger and larger, the cost of handling the buoyancy of water by the dock's self weight is increasing. Therefore, most dock designs give priority to the decompression and drainage structure. The development trend of dock structure is from heavy to light, from integral structure of dock wall and bottom plate to separated structure.
Source: Jiangmen floating dock factory http://www.campuppet.com/