A cofferdam is a temporary structure designed to keep water and/or soil out of the excavation in which a bridge pier or other structure is built. When construction must take place below the water level, a cofferdam is built to give workers a dry work environment.
In which condition a cofferdam is not required?
Explanation: The cofferdam is generally constructed at the site of work. The cofferdam should be reasonably watertight. It may either raised on the impervious soil or may be extended to impervious strata through pervious soils. It should be noted that absolute water tightness is not desired in a cofferdam.
What do cofferdams mean?
A cofferdam means an empty space provided in a ship so that compartments on each side have no common boundary; a cofferdam may be located vertically or horizontally.
Are cofferdams permanent?
Cellular cofferdams can be left in place as permanent structures. They can also provide crane access to different areas of the work site if a road is built across the top.
Which is the simplest form of cofferdam?
2. Earth-Type: It is the simplest type of cofferdam. It consists of an earth bank with a clay core or vertical sheet piling enclosing the excavation. It is used for low-level waters with low velocity and easily scoured by water rising over the top.
How deep can cofferdams go?
Wooden sheet pile cofferdam is suitable for up to 9 feet, steel sheet pile is suited up to 18 feet head of water, similar to concrete, which suitable when headroom is limited.
What is the difference between cofferdam and caisson?
The main difference between the two is that a cofferdam is a temporary structure which is removed after completion of the work, whereas a caisson is built to remain in place as part of the completed structure.
How long does it take to install a cofferdam?
The setting of the template takes about a half a day. The falsework is usually installed in one day. The spuds (H-piles) are driven through the cofferdam frame to provide an exact location and plumbness to the frame.
Are cofferdams safe?
Safety when using a cofferdam begins with a proper site inspection. … A water filled cofferdam is generally a safer solution to water intrusion issues than traditional methods such as pile-driven cofferdams as they mean your crew will be spending less time in the water.
When the depth of water is more say 4.5 to 6 m which cofferdam is used?
4. Single Walled Cofferdam. This type of cofferdam is used in places where the area to enclosed is very small and, the depth of water is more, say 4.5 to 6.0. Timber piles are known as guide piles are first driven deep into the firm ground below the river bed.
What is the importance of cofferdams?
Cofferdams help protect construction crews, materials, and equipment. Additionally, they help protect completed work until your structures are ready for contact with the water. Therefore, cofferdams are an important part of the marine construction process.
How do caissons work?
A caisson is sunk by self-weight, concrete or water ballast placed on top, or by hydraulic jacks. The leading edge (or cutting shoe) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner; it is usually made of steel.
What is gravity cofferdam?
A gravity dam is a massive, man-made concrete dam designed to hold large volumes of water. Because of the heavy concrete used, it is able to resist the horizontal thrust of the water, and gravity essentially holds the dam to the ground.
Are caissons still used?
Caissons are generally used as the means to complete new construction, and may act as a cofferdam of sorts while the construction is ongoing. Cofferdams however, are not part of the permanent structure, and are typically employed to perform repairs or maintenance on the structure.
Who invented caissons?
History. The caisson lock was first demonstrated at Oakengates on a now lost section of the Shropshire Canal in 1792, where its inventor, Robert Weldon (b:? 1754 to d:1810) built a half-scale model.
What is cofferdam and its types?
Rockfill cofferdam. Single-walled cofferdam. Double-walled cofferdam. Braced cofferdam. Cellular cofferdam (Circular or diaphragm type)
Which is the most common type of cofferdam?
To better understand the capabilities of cofferdams, consider the differences between the three most common types.
- Braced Cofferdams.
- Cellular Cofferdams.
- Aqua-Barrier Inflatable Cofferdam.
Are dams hollow?
Hollow gravity dam. A dam constructed of concrete and/or masonry on the outside but having a hollow interior relying on its weight for stability. Crib dam. A gravity dam built up of boxes, crossed timbers, or gabions filled with earth or rock.
Is the simplest form of joint?
2. ___________________ is the simplest form of joint. Explanation: Lapped joint is form by putting the two Timber pieces one over the other from a short distance and the binding them together by means of iron straps or Stirrups.
What are the horizontal forces that are prone to act on a well Foundation?
Explanation: A well foundation is liable to the following horizontal forces: i) force on account of water current ii) wind forces iii) seismic forces iv) earth pressure v) centrifugal forces. Explanation: Based on the assumptions done by Banerjee and Gangopadhyay in 1960, the analysis of well foundation can be done.
Which of the following is the most commonly used shallow foundation?
Which of the below is the most commonly used shallow foundation? Explanation: In spread footing, load is transmitted through an isolated column or wall to the subsoil; hence this is most common type of foundation.
What is structural shoring?
Shoring is the process of temporarily supporting a building, vessel, structure, or trench with shores (props) when in danger of collapse or during repairs or alterations. Shoring comes from shore, a timber or metal prop. Shoring may be vertical, angled, or horizontal.
What is Storage Dam?
Storage dams:
As the name suggests, this dam is constructed to store the water during the rainy season when there is a large flow of water. Storage dams store water for hydroelectric power generation, irrigation or flood control project or may be used for improved habitat for fish and wildlife.