The different types of cofferdams are listed below.
- Braced Cofferdam
- Cellular Cofferdam
- Earthen Cofferdam
- Rockfill Cofferdam
- Single-walled Cofferdam
- Double-walled Cofferdam
We will learn about these six types of cofferdams dams in detail.
Table of Contents
1. Braced Cofferdam
A braced cofferdam is a type of temporary structure that is used to create a dry area in which construction or repair work can be carried out underwater. It consists of two piles that are driven into the bed of a body of water, and lateral support is provided by wooden cribs that are installed in alternate courses to form pockets. These pockets are then filled with stone and earth to create a stable foundation. The framework of the cofferdam is constructed on land and then floated to the site where it is needed.
To begin the construction process, the layers of sand and loose material overlying the hard bed are dredged out and the cribs are sunk into position. The bottom of each crib is shaped to fit the contours of the bedrock to ensure stability. Once the pit has been dewatered, the structure can be concreted. Once the concreting is complete above the water level, the cofferdam can be removed.
Braced cofferdams are used in situations where it is difficult to drive piles into the bed of the water directly. They provide a stable, dry area for construction or repair work to be carried out, and can be easily dismantled and removed once the work is finished.
2. Cellular Cofferdam
Cellular cofferdams are a type of dam used in the construction of dams, locks, and weirs when the water depth exceeds 20 meters. These dams are made by driving straight steel sheet piles into the ground, arranging them to form interconnected cells. The cells can be constructed in various shapes and styles to suit the needs of the site. Once constructed, the cells are filled with a stable material such as clay, sand, or gravel to provide stability against various forces.
3. Double Walled Cofferdam
Double walled cofferdams are used when the construction site is large and the water is deep. Single-walled cofferdams are not practical because they would need too many supports. Double-walled cofferdams are stronger and can hold water up to 12 meters high. They have two walls instead of one. To build a double-walled cofferdam, piles are driven into the water bed and connected with bolts. The space between the walls is filled with soil to keep the water out. The sheet piles are also driven deep into the ground to prevent leaks.
4. Single Wall Cofferdam
A single wall cofferdam is a type of dam used for construction in deep water, typically for building bridges. It is made by driving wooden or steel sheets into the river bed around the construction area. The sheets are held in place by wales, which are bolts connecting the sheets on both sides. Sandbags may also be placed on either side of the walls to increase stability. To use a single wall cofferdam, the water inside the dam is pumped out and construction can begin.
5. Rock Fill Cofferdam
Rock fill cofferdam is made from easily accessible rock at the construction site, are a type of dam that is preferred due to their high permeability. To prevent water from seeping through, an impervious layer of soil is included in the dam’s design. These dams can be up to 3 meters tall and have a slope ratio ranging from 1:1.5 to 1:125, with the slope on the water side being steep to protect against wave action.
6. Earthen Cofferdam
An earthen cofferdam is a temporary dam that is constructed in an area where the water is relatively shallow and the current is slow. It is typically made from local materials such as clay, fine sand, or soil. The height of the dam is typically about one meter higher than the maximum water level, with a “freeboard” of another meter at the top to allow for waves. The slope of the dam is usually 1:1 or 1:2, and the side facing the water is reinforced with rubble stones to protect it from the force of the water. Sheet piles may also be driven into the center of the dam to prevent water from seeping through. Once the cofferdam is in place, the water on the other side can be pumped out, allowing for construction to take place.