In geotechnical engineering, a caisson ( or ) is the waterproof retaining structure used, for example, to work on foundations of bridge docks, for the construction of concrete dams, or for ship repair. It is built so that water can be pumped out, keeping the work environment dry. When the dock is built using an open caisson, and it is impractical to reach the appropriate soil, friction poles may be pushed to form the appropriate foundation. This stack is connected by the base upon which the column pole is erected.
Video Caisson (engineering)
Etimologi
Borrowed from French caisson , from Italian cassone , which means box .
Maps Caisson (engineering)
How caisson works
The shallow Caisson may be exposed to air, while the pneumatic caisson , which penetrates the soft mud, is sealed at the top and filled with compressed air to keep the water and mud out at depth. Airlock allows access to the room. The worker moves mud and rock debris (called dirt) from the edge of the workroom to a hole filled with water, connected to a tube (called a dirt tube) to the surface. The cranes on the surface remove the soil with a clamshell bucket. The pressure of the water in the tube balances the air pressure, with the excess air coming out of the sewage tube. The pressurized air flow must be constant to ensure regular airflow for workers and prevent excessive mud or water flow at the bottom of the caisson.
Installation
To install the caisson in place, it is brought down through the soft sludge until the suitable foundation material is encountered. While the bedrock is preferred, stable, hard sludge is sometimes used when the bedrock is too deep.
Danger found in pressured caissons
Construction workers who leave the caisson-pressurized environment must decompress at a level that allows the release of inert gases free of symptoms dissolved in body tissues if they wish to avoid decompression disease, a condition first identified in caisson workers, and originally named "Caisson disease" in recognition of the dangers work. The construction of the Brooklyn Bridge, built with the help of pressurized caisson, resulted in many workers being killed or permanently injured by caisson disease during its construction. Barotrauma in the ear, sinus and lung cavities and osteonecrosis of dysbaric are other risks.
Other uses
Caissons have also been used in hydraulic elevator installation where single-stage ram is installed beneath the ground.
Caissons, codenamed Phoenix , is an integral part of the Mulberry port used during the Allied World War II invasion of Normandy.
Type
The four main types of caisson are caisson boxes , caisson open , caisson compressed air and monolith caisson .
Square
A caisson box is a prefabricated concrete box (has sides and bottom); it is set on a prepared basis. Arriving on the spot, it is filled with concrete to be part of a permanent job, such as the foundation for the bridge dock. Hollow concrete structures are usually less dense than water so the caisson box has to be replied or anchored so as not to float until it can be filled with concrete. Sometimes elaborate retaining systems may be needed, such as in tidal zones. Adjustable retaining systems combined with GPS surveys allow engineers to position the caisson box with precise accuracy.
Open
An open caisson is similar to a caisson box, except that it does not have a down face. It is suitable for use in soft clay (eg in some rivers), but not for a place where there may be a large obstacle in the soil. An open caisson used in soft base or high water table, where open ditch excavation is impractical, can also be used to install deep pits, pumping stations and reception/launch holes for micro tunneling, pipe bombing and other operations.
A caisson is drowned by a self-contained, concrete or water loader placed on top, or with a hydraulic jack. The spearhead (or cutter ) of the caisson tilts out at a sharp angle to help drown vertically; usually made of steel. Shoes are generally wider than caisson to reduce friction, and the cutting edge may be supplied with pressurized bentonite slurry, which swells in the water, stabilizes the settlement by filling the hollows and cavities. An open caisson can be filled with water during drowning. The material is excavated with a clamshell excavator bucket in the crane.
The level of subsoil formation may still be unsuitable for excavation or carrying capacity. The water in the caisson (due to the high water table) balances the upthrust strength of the soft ground underneath. If dried, the base can "pipe" or "boil", causing the caisson to sink. To solve this problem, the stack can be pushed from the surface to act as:
- The load-bearing wall, where they send the load to the deeper ground.
- Anchors, because they resist floatation due to friction at the interface between their surface and the surrounding earth where they are moved.
The part of the H-ray (a typical column part, due to resistance to bending in all axes) can be pushed at a "scratched" angle to rock or other stronger soil; H-beam is allowed to extend over the base. A reinforced concrete plug can be placed underwater, a process known as Tremie concrete placement . When the caisson is removed, the plug serves as a pole cover, holding up the upward force of the soil layer.
Compressed air
A compressed air caisson has the advantage of providing dry working conditions, which is better for placing concrete. It is also suitable for the foundations on which other methods may lead to the completion of adjacent structures.
Monolithic
A monolithic caisson (greater than just monolith ) is greater than other caisson types, but is similar to an open caisson. These kind of Caissons are often found on the dock walls, where resistance to the impact of the vessel is required.
Boat boats caissons
The word caisson is also used as a synonym for the moving portion of the caisson lock, the lift of the canal and the slope at which the ship and vessel rest while being lifted from one channel elevation to another; water is stored on the inside of the caisson, or removed from the caisson, in accordance with the principle of operation of each.
Structural Suai
Caisson is also sometimes used as a colloquial term for a reinforced concrete structure formed by pouring into a vacuum cylinder, usually by placing the caisson form below the level in the open excavation and pouring once the slurping is complete, or by drilling in the class, although this may cause problems with deep caissons, since unsupported excavations may collapse before the caisson form can be inserted. In this way, the earth is placed around a blank form of caisson providing stability and strength, allowing the concrete to be poured with fewer complications and with less risk than the form of explosion. While, technically speaking, only the form itself is actually a caisson, it's not uncommon for any concrete cast pillars below the class to be called, just, a caisson .
Ventilation filtration system
The word caisson is also used as a name for airtight housing for ventilation filters in facilities that handle hazardous materials. Housing usually has upstream compartments for pre-filter elements and downstream compartments for high-efficiency filter elements. It may have several sets of compartments. Housing has a gas access door to allow changes out of the filter element. Housing is usually equipped with a connection point used to test filter efficiency and monitor changes in differential pressure in the filter media.
See also
- Cofferdam, temporary waterless structures built in places, sometimes around work areas as well as open caisson.
- Offshore geotechnical engineering, for information on geotechnical considerations.
Patent
- AS. Patent 123,002 - Improvement of sub-water foundation construction
References
External links
- Works related to Caisson on Wikisource
Source of the article : Wikipedia
0 Comments