What Is Cofferdam In Construction?
What Is Cofferdam In Construction?
Definition Of A Cofferdam
A cofferdam is a temporary watertight structure that is built to keep water out of areas during construction. It is typically made of steel, concrete, or wood and can be either free standing or anchored to the existing ground.
Cofferdams are most commonly used to divert waterways and dewater areas when constructing bridges, dams, docks, and other similar structures. They can also be used in sewage treatment plants and other wet industrial processes such as agricultural irrigation systems.
By building a structure that seals out the water from the construction site, excavation work can proceed without being hampered by water-related obstacles.
Generally, a cofferdam is a structure that is used to separate a work area from water so that construction or repair work can be done. It does this by retaining water on one side and allowing the work area to be drained, enabling activities such as pouring concrete, digging, welding, and more.
Cofferdams can be used in various situations such as bridge construction and riverbank stabilization, providing a secure foundation for work to commence on these otherwise inaccessible areas.
With their ability to shield engineers from unpredictable weather conditions and other risks that come with working near bodies of water, cofferdams are often vital components of large-scale infrastructure projects
Types Of Cofferdams In Construction
There are several different types of cofferdams that come in various configurations, sizes, and materials. These include box-type, braced, double-walled sheet pile, cellular, earthen, single-walled sheet pile, and Portadam systems.
Each of these types has its own benefits and drawbacks depending on the project’s specific location, site conditions, and budget. The following are three examples of cofferdams, along with information on their construction and uses:
Braced Cofferdams
A braced cofferdam is a temporary structure used to enclose and protect a work area from water. It is created by driving a wall of sheet piles into the ground and bracing them with struts or beams to form a box-like shape.
These cofferdams are often used for bridge pier and abutment repairs and can be effective in providing a dry workspace. However, it is important to ensure that they are properly sized and equipped with an emergency evacuation plan in case of an accident, as confined spaces can be challenging to escape from in an emergency.
Cellular Cofferdams
Cellular cofferdams are large-scale construction projects that create a watertight barrier to enclose a work area. They are created by driving sheet piles in a circular pattern to form a series of interconnected cells.
There are two types of cellular cofferdams: diaphragm, which have circular arcs at the sides connected to straight walls, and circular, which are made up of large circular cells connected to smaller ones.
These structures are often used in dam construction, barrier walls, and dock facilities, and can be left in place as permanent structures or provide access to different parts of the work site with a road on top.
Portadam Systems
The Portadam system is a unique temporary cofferdam option that does not require ground penetration for installation. This minimizes subsurface risks, such as environmental or schedule delays, that are often associated with sheet piling.
The Portadam consists of frames assembled on the bed of a river or lake enclosing the area that needs to be dewatered. A vinyl fabric membrane and impervious fabric sealing sheet are then placed over the frames to secure the area and allow for dewatering.
The units can reach up to 12 feet high, making them a potential solution for low-cost, temporary access to work areas in shallow water. However, it is important to be cautious when using Portadams in rivers or lakes with strong currents, fluctuating water levels, ice, or wind seiches.
Advantages And Disadvantages Of Using A Cofferdam
A cofferdam is a temporary barrier used in construction to isolate a particular area of water, creating a dry space for the duration of the project.
While this technique can be immensely helpful in aiding large-scale projects that require access to otherwise submerged areas, there are some advantages and disadvantages associated with its use.
Some advantages include decreased build time due to dry conditions as well as providing increased safety during construction due to reduced risk of flooding.
On the other hand, disadvantages include high cost of building and maintenance as well as environmental impacts from using cofferdams, such as disruption of aquatic habitats during their setup and removal.
Safety Of Cofferdams
Cofferdams can be risky to install and maintain due to factors such as ice flows, vessel traffic, soil conditions, and flood events. It is essential to have an emergency response plan in place, especially when working in confined spaces inside a cofferdam.
To ensure the success of a project, it is crucial to have effective seals and dewatering systems with backups. Although working around water can be challenging for contractors, cofferdams provide a reliable method for temporarily removing water from the work area.
To ensure a safe and timely project completion, it is important to understand the various types of cofferdams and their strengths and limitations.
Conclusion
In conclusion, cofferdams are essential tools in the construction industry. They can be used to dewater and excavate, provide access for workers, and keep concrete workspace dry during construction projects.
Cofferdams are commonly used for bridge piers, underground mines, dams, locks, shipwrecks repair and more. They offer a safe, cost-effective way to perform construction work in water environments and ensure the safety of workers and equipment.
