Cofferdam Types – Materials and Construction Techniques

Cofferdam types are essential in civil engineering. They act as temporary structures designed to create dry work areas in water bodies like rivers, lakes, and coastal regions. These watertight barriers prevent water intrusion, allowing submerged foundation construction. Cofferdam construction involves building enclosures within water bodies to create a dry environment. Engineers use various types of cofferdams like sheet pile, earth-filled, and double-walled types, circular type cellular cofferdams etc. based on the project’s requirements. They pump water out from the site. This creates a dry, controlled environment. This ensures safe, clean, and efficient construction in challenging water-based locations. The correct choice of cofferdam types allows engineers to handle various depths, soil conditions, and construction goals successfully.

This article explores the various types of cofferdams. It covers their construction methods and applications. It also discusses key considerations for successful implementation in underwater construction projects.

What is a Cofferdam?

Cofferdams are innovative structures that play a crucial role in underwater construction projects. These watertight barriers temporarily hold back water, enabling construction teams to work on submerged foundations safely and efficiently. The primary function of cofferdam construction is to create a dry workspace. This is done by pumping out the water inside once the structure is in place. This is essential for projects such as bridge construction, underwater excavation, and marine infrastructure development.

There are various types of cofferdams, each tailored to the specific requirements of the construction site. Cofferdams range from simple sheet pile designs to more intricate cellular designs. These cofferdam types are engineered to withstand the pressure of surrounding water. Proper cofferdam construction ensures a stable work environment, allowing for efficient operations even in challenging conditions. Understanding the different types of cofferdams is vital for selecting the right solution for each project. Let us dive deep into the Types of Cofferdams and their applications.

Applications of Cofferdams Types

Cofferdams provide a safe, dry environment necessary for working on submerged structures and foundations. They are indispensable in creating controlled conditions for underwater construction projects. This allows engineers and workers to access areas that would otherwise be inaccessible. These areas might also be extremely challenging to work in.

The versatility of cofferdams makes them suitable for a wide range of applications in civil engineering and construction.

• Essential for creating safe, dry workspace in submerged environments.
• Used extensively in constructing and repairing bridge piers and foundations by isolating the work area from water.
• Engineers employ various types of cofferdams for dam and hydroelectric power plant projects to support construction, upgrades, or repairs.
• Key in facilitating marine and harbor infrastructure work, enabling wharf, pier, and harbor facility construction and maintenance.
• Vital for underwater excavation, providing a controlled and stable environment for submerged structures.
• Ensures efficient and safe completion of civil engineering projects in aquatic environments through proper construction methods.

Materials Used For Cofferdam Construction

The construction of cofferdams involves various materials depending on the type and scale of the project. The main materials used for cofferdam construction are as follows

1. Steel Sheet Piles: Engineers utilize steel sheet piles in most cofferdams, especially in cellular and braced types, to form the walls. They drive these piles into the ground, creating a watertight barrier that retains soil and prevents water intrusion.
2. Fill Materials: Workers fill the cells or spaces between the sheet piles with materials like sand, gravel, or clay, providing stability and resistance to water pressure.
3. Bracing Members: In braced cofferdams, engineers install steel beams or struts to offer lateral support to the walls and maintain their alignment during construction.
4. Geotextiles: Engineers occasionally use geotextile fabrics for soil separation, enhancing the overall strength and integrity of the cofferdam structure.
5. Concrete: For permanent or long-term cofferdams, such as those used in bridge pier construction, workers pour concrete into the structure. This helps to reinforce the walls or base.
6. Water Pumps: Although not a material, engineers deploy water pumps to keep the excavation area dry. They constantly remove seepage from inside the cofferdam.

Engineers select these materials based on factors such as water depth, soil conditions, and the project’s duration. The specific requirements of each construction site dictate the most suitable materials to ensure stability and effectiveness. .

Cofferdam Types

There are several types of cofferdams used in construction, each suited to different water depths, soil conditions, and project requirements. Understanding the various cofferdam designs is crucial for selecting the most appropriate solution for a given application.

Depending on the design requirements, water depth, soil conditions, type of material used, etc., coffer dams are classified into many types.

• Earthen cofferdam
• Rock fill cofferdam
• Single wall sheet pile cofferdam
• Double-wall sheet piling cofferdam
• Braced cofferdam
• Cellular cofferdam

Earthen cofferdam – Common Cofferdam types

Engineers commonly use earthen cofferdams as temporary structures, constructing them from soil or gravel. These cofferdams are ideal for shallow waters with low flow velocity. As one of the common types of cofferdams, earthen cofferdams creates a barrier. This barrier enables dewatering of the enclosed area for construction purposes. Engineers carry out cofferdam construction by placing soil material to block water and then pumping it out to keep the area dry. This cofferdam type proves to be economical and can utilize locally available materials. However, contractors limit earthen cofferdams to shallow waters, and they can erode in areas with strong currents.Proper maintenance and regular inspections are essential to ensure the integrity of these structures in active water environments.

For extensive excavations, construction teams use earthen cofferdams, which require a large base area. They place an impervious clay core or sheet piles in the center to resist water pressure and seepage. To prevent scouring, workers apply stone-pitching on the upstream side. However, these types of cofferdams are not fully waterproof, requiring pumps and additional systems to manage water.

Rock-fill cofferdam – Second Popular Cofferdam types

A rock-fill cofferdam is a type of cofferdam that uses boulders or rocks to create a barrier. It is similar to earthen cofferdams but has greater strength and durability. Cofferdam construction with rock-fill materials is ideal for areas with moderate water flow. It is also suitable for weak soils where erosion is a concern. This cofferdam type provides better resistance to erosion. It is more suitable for environments where water currents are stronger. However, rock-fill cofferdams are more expensive and labor-intensive due to the heavier materials required and the need for precise placement.

Although these cofferdams offer enhanced durability, they are still a temporary solution and may require pumps to manage water seepage.When compared to earthen cofferdams, rockfill cofferdams are superior. The cost and availability of rocks in the area influence the choice of rockfill dams. Engineers should limit the rockfill dam’s maximum height to under 10 feet. They line the pervious rockfill area with an impervious clay layer to prevent seepage and ensure dam stability.

Merits: Excellent erosion resistance and suitable for moderate water flow.

Demerits: Higher cost and labor demands compared to other types of cofferdams, such as earthen cofferdams. Despite these drawbacks, rock-fill cofferdams are a reliable option for challenging construction sites.

Single wall sheet pile cofferdams

A single-walled sheet pile cofferdam is a type of cofferdam used in shallow waters. It is typically less than 6 meters deep. It is used for localized work like bridge pier construction. Cofferdam construction involves driving timber sheets as guide piles and then securing steel sheets inside as the primary support. In deeper water, guide piles may be steel sections. Engineers bolt wooden wales or runners at intervals to maintain the distance between internal and external piles. They place sandbags on both sides for added stability. Once they pump out the water, construction proceeds smoothly. For clay, the penetration depth should be approximately 1 meter, 0.5-0.75 meters for sand, and 0.25-0.5 meters for gravel, etc.

Merits: Single-walled cofferdams are cost-effective and simple to construct for small-scale projects in shallow waters. They are ideal for quick installations in localized areas.

Demerits: These cofferdams are less stable in deep water and cannot withstand strong currents. They also require additional stability measures, such as sandbags, which can increase the complexity of construction. Penetration depth varies depending on the soil type, affecting overall durability.

Double-wall sheet piling cofferdam

Double-walled cofferdams are a type of cofferdam used in deep waters. Engineers use them for projects requiring enhanced stability. Examples include bridge or pier construction. Unlike single-walled cofferdams, they feature two parallel walls. The walls are usually made of steel or timber sheet piles. These walls are filled with materials like sand, gravel, or concrete. This design provides greater strength and resistance to water pressure. It also withstands external forces, making it suitable for areas with strong currents or deeper water levels.

Double walled Cofferdam construction involves driving both walls into the riverbed or seabed. The space between them is filled to provide additional support. The double-walled structure helps prevent seepage and minimizes the risk of collapse during dewatering. Once the area is dry, construction can safely begin.

Merits: High strength, ideal for deep water and high-pressure environments, offers better protection against seepage.

Demerits: More expensive and labor-intensive compared to other types of cofferdams like single-walled or earthen cofferdams.

Braced Cofferdams

A braced cofferdam offers a solution when driving piles into the bed underwater is difficult. Engineers drive two piles into the bed and laterally support them using wooden cribs, which are installed in alternating courses. These cribs create pockets that are filled with stones and earth to stabilize the structure.

The cofferdam framework, typically made from logs, is constructed on land and then floated to the worksite for assembly. Workers dredge out loose material above the impervious bed and submerge the cribs to match the bedrock’s contours. After dewatering the pit, they pour concrete to form the foundation. Once the concrete cures above the waterline, the cofferdam is removed, leaving a stable base for ongoing construction activities. This method effectively provides a dry work area, showcasing the advantages of braced cofferdams.

A braced cofferdam serves as a temporary enclosure that enables construction in shallow water or earth by utilizing vertical or horizontal sheeting supported by internal struts. This design effectively keeps water out, creating a dry environment essential for projects like bridge construction or aquatic maintenance. Braced cofferdams are versatile, supporting shallow trench excavations and providing bracing for multi-level basements. They are often chosen for constructing bridge piers and abutments due to their cost-effectiveness compared to cellular cofferdams and caissons in depths up to 40 ft. However, constructing them in extensive, deep excavations can be challenging, necessitating alternative excavation methods.

Cellular Cofferdam

A cellular cofferdam is a type of temporary structure used to dewater large areas, particularly in deep water construction projects such as dams or bridge piers. It consists of interconnected steel sheet piles forming either circular type cellular cofferdams or diaphragm cells filled with materials like sand, gravel, or clay. These cofferdams are ideal when large surface areas need to be enclosed and when the water depth is considerable.

This category of cofferdams includes two main types. Engineers design circular type cellular cofferdams with round cells, while diaphragm cellular cofferdams use straight diaphragms connected by arcs of sheet piles.. This construction provides stability due to the weight of the fill material and the interlocked design. Cofferdam construction of this type is robust and cost-effective in terms of material use.

The selection of cofferdam types depends on the specific project requirements, including water depth and the size of the area to be enclosed. Engineers typically use cellular cofferdams in deep water environments because of their ability to provide stability and resistance to high water pressures.

Key Takeaways

• Cofferdams are essential temporary structures used in underwater construction to create a dry environment for submerged projects.
• Various types of cofferdams—including earthen, rock-fill, single-walled, double-walled, braced, and cellular—are used based on water depth, flow conditions, and project requirements.
• Materials such as steel sheet piles, fill materials, and concrete are chosen based on the project’s complexity, water pressure, and soil conditions.
• Cofferdams are widely applied in bridge construction, dam building, and marine infrastructure projects, making them indispensable for safe and efficient underwater construction.

Conclusion

Cofferdams provide a reliable solution for underwater construction projects by creating a controlled, dry work area. Their versatility in design—from earthen to cellular types—ensures they meet the specific demands of different environments. Choosing the right type of cofferdam is crucial. Selecting the appropriate materials guarantees stability and safety during construction. This enables successful completion of projects in challenging aquatic settings.