Caisson (engineering)

A caisson is a large, strong box.

It helps people build in water. People use them to make bridge legs. They also help fix big ships.

Some caissons are open at the bottom. They sink through soft mud. They stop when they hit hard ground.

Other caissons are closed at the top. They use air to push water out. This keeps the inside dry for workers. This makes it easy to use concrete.

Workers move mud and rocks out of the box. They use tools to clean it. This keeps the space ready for building.

These big boxes help us make strong things.

A caisson is a strong, watertight structure.

Engineers use them to build in water. They help make bridge legs and big dams. They can even help fix ships.

There are different kinds of caissons. A box caisson is a big, hollow box. It has a bottom but no top. Workers sink it into the mud. Once it stays in place, they fill it with heavy weight called ballast. This keeps it from moving.

An open caisson is like a box without a bottom. It sinks into soft mud. Workers use a crane to scoop out the mud from inside.

This lets the caisson go deeper.

A pneumatic caisson is a special type. It is a bottomless box sealed at the top. It uses compressed air, which is air pushed under high pressure. This air pushes the water and mud out. This keeps the workspace dry for the workers. People often call these workers "sandhogs." They move mud and rocks out through a tube. When the caisson hits hard bedrock, the workers fill the box with concrete. This creates a solid base for building.

A caisson is a strong, watertight structure used for big jobs. Engineers use them to build things in water or soft ground. They are very important for making bridge piers and concrete dams. They can even help with the repair of ships.

These structures allow people to work in places that would normally be too wet. By using a caisson, builders can create a dry space deep under the water. This makes it much easier to build a solid foundation.

There are several ways a caisson works depending on its type. A box caisson is a hollow box with a bottom but no top. It is set down on a flat base and filled with ballast. Ballast is heavy material that keeps the box from moving.

An open caisson has no bottom at all. It sinks into the mud using its own weight or hydraulic jacks. Workers use a clamshell excavator on a crane to scoop out the mud from the inside.

A pneumatic caisson is a special kind of bottomless box. The top is sealed tight to hold in compressed air. This high-pressure air pushes the water and mud out of the way.

This creates a dry workspace for the people inside. These workers are often called sandhogs in America. They move mud and rocks, called muck, through a tube to the surface. When the caisson reaches hard bedrock, the workers fill it with concrete.

Engineers have used caissons for a long time. We can see examples from the 19th century. The Royal Albert Bridge was finished in 1859. The Eads Bridge was completed in 1874. The famous Brooklyn Bridge was finished in 1883 using pressurized caissons.

Working with air pressure was very hard for those builders. Many workers became sick from a condition called caisson disease. This happened because they had to change air pressure slowly. It was a very dangerous job for the sandhogs.

You might see caissons used in many different ways today. They are used to install hydraulic elevators below the ground. During World War II, special caissons named Phoenix were used in Normandy. They were part of the Mulberry harbours.

The word is also used for parts of canal locks. These parts lift boats from one height to another. Whether building a bridge or a canal, caissons help us master the water.

In geotechnical engineering, a caisson is a watertight retaining structure. These heavy-duty tools allow engineers to perform construction in difficult environments. They are essential for building bridge piers and concrete dams. They are also used for repairing ships.

By creating a controlled workspace, caissons enable builders to reach stable ground deep beneath water or soft soil. This process ensures that massive structures have a solid foundation to rest upon.

The installation process depends on the type of caisson used. Generally, a caisson is brought down through soft mud. It continues to sink until it reaches a suitable foundation material. While bedrock is the preferred stopping point, engineers sometimes use stable, hard mud if the bedrock is too deep. This movement is achieved through various methods. Some caissons sink by their own weight. Others use concrete or water ballast placed on top. In some cases, engineers use hydraulic jacks to push the structure down into the earth.

There are four primary types of caissons: box, open, pneumatic, and monolithic. A box caisson is a prefabricated structure with sides and a bottom, but it is open at the top. It is typically placed on a prepared, flat base. Because hollow concrete is often less dense than water, engineers must secure box caissons to prevent them from drifting. They may use elaborate anchoring systems or GPS surveys for pinpoint accuracy. Once positioned, the box is filled with ballast to become a permanent part of the foundation.

An open caisson is similar to a box caisson, but it lacks a bottom face. This design is ideal for soft clays found in riverbeds. However, they are not suitable for areas with large underground obstructions. These structures can also be used to install deep manholes or pump stations. To help the caisson sink vertically, the leading edge, or cutting shoe, is sloped at a sharp angle. This shoe is usually made of steel and is wider than the caisson to reduce friction.

Sometimes, pressurized bentonite slurry is supplied to the edge to fill voids and stabilize the settlement.

A pneumatic caisson, also called a pressurized caisson, is a bottomless box sealed at the top. This top seal allows the interior to be filled with compressed air. This air pressure keeps water and mud from entering the workspace at great depths. Workers inside these chambers are known in American English as sandhogs. They move debris, called muck, from the workspace into a water-filled tube called a muck tube. A crane at the surface then removes the soil using a clamshell bucket.

Pneumatic caissons offer the advantage of dry working conditions, which is better for placing concrete. However, this method carries significant health risks. Workers must decompress slowly when leaving the pressurized environment. If they do not, they may suffer from decompression sickness, once known as caisson disease. This condition involves the release of inert gases in body tissues. It can cause barotrauma to the ears, sinuses, and lungs, or lead to dysbaric osteonecrosis. During the construction of the Brooklyn Bridge, many workers were killed or permanently injured by this disease.

History shows the growing importance of caisson engineering throughout the 19th century. The Royal Albert Bridge was completed in 1859. The Eads Bridge followed in 1874. The Brooklyn Bridge was finished in 1883. These projects demonstrated how caissons could conquer challenging waterways. Beyond bridges, caissons have various other roles in modern technology. They are used to install single-stage ram hydraulic elevators below ground level. During World War II, caissons codenamed Phoenix were used in the Mulberry harbours during the invasion of Normandy.

The term caisson is also used in other engineering contexts. In canal systems, it refers to the moving trough in a caisson lock that lifts ships between elevations. In ventilation, a caisson is an airtight housing for filters in facilities handling hazardous materials. It may contain multiple compartments for pre-filters and high-efficiency filters. Finally, in structural engineering, the term is sometimes used colloquially for any reinforced concrete pillar formed by pouring concrete into a hollow shape below grade.