Working around water poses a plethora of challenges. There are always two parts of a water-based project, the above and below water sections. Access to the above water section is easy, however when working below the waterline access is not that easy. One of the more apparent issues is what do you do when the water is in the way of your work? One solution is to build a cofferdam.
A cofferdam is a structure that retains water and allows a work area to be dewatered so that crews can pour concrete, excavate, repair, weld, etc.
There are numerous configurations, sizes, and material options when it comes to cofferdams. Below are a few examples:
Cofferdams can be customized to fit the needs of any project. Each of these systems has their pros and cons, depending on conditions such as site location, site conditions, and price restrictions.
Below we take a look at three types of cofferdams, their construction, and applications:
Braced cofferdams are made by vertically driving a single wall of sheet pile around the work area. This type of cofferdam is typically driven into the shape of a box. Struts, or beams, then brace the walls to keep them from collapsing inward, which is where it gets its name. When dewatered, a cofferdam will withstand the force of the water while allowing crews access to the work area. This cofferdam is an excellent choice for bridge pier and abutment repairs. These cofferdams may form confined space work conditions, so it is imperative that they are sized correctly for all the tasks that need to be accomplished for the project. Emergency evacuation should also be planned as it can be very difficult to remove an injured person from a deep, confined space.
There are two types of cellular cofferdams, diaphragm and circular. Diaphragm types are cofferdams with circular arcs at the sides, connected to straight diaphragm walls. Circular types are large circle-shaped cells, connected to one another by slightly smaller circular cells. Projects, where cellular cofferdams come into play, include dam construction projects, barrier walls, and dock facilities. 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.
*Source: Portadam.com
There are many risks involved in installing and maintaining an effective cofferdam such as ice flows, current, vessel traffic, rock fissures, flood events, soil conditions and more. When working inside a cofferdam, crews are often in a confined space, meaning an emergency response plan is a must. For the cofferdam itself, maintaining an effective dewatering plan is crucial for successful project completion. By having effective seals and dewatering systems with backups, you can make the difference between the success and failure of a project.
Working around water is going to be an ever-present hurdle for contractors. Fortunately, cofferdams are around to offer a practical, proven method for selectively and temporarily removing water from the work area. Understanding which type of cofferdam is best as well as knowing their strengths and limitations will allow you to complete your project safely and on time.
For more educational content on structural projects, view Helical Piles 101 and see how we help our clients strengthen their foundations.