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How cofferdams are built

How Are Cofferdams Built?

Cofferdams, temporary structures created to exclude water and soil from construction sites, play a crucial role in various projects. Among the different types, sheet pile cofferdams offer a robust and versatile solution, particularly effective for deep excavations or challenging environments. This blog delves into the construction process of these impressive structures, focusing on the specifics of sheet pile implementation.

Understanding Sheet Piles

Imagine interlocking steel sections, forming a continuous wall that can withstand significant forces. These are sheet piles, typically made of high-strength steel and designed to efficiently interlock, creating a watertight barrier.

Choosing the Right Type:

The optimal cofferdam type depends on project requirements. Here are the three main categories:

  • Cantilever Sheet Pile Cofferdams: Suitable for shallow excavations and stable soil conditions, these self-supporting cofferdams rely on the sheet piles’ embedded depth to resist inward pressure.

  • Braced Sheet Pile Cofferdams: Deeper excavations or weaker soil necessitate additional support. Braced cofferdams incorporate a system of internal steel beams and struts that distribute pressure evenly, ensuring stability.

  • Anchored Sheet Pile Cofferdams: Complex projects facing strong water currents or unstable ground often require external support. Anchored cofferdams utilise sturdy cables connected to external anchor points, pulling the sheet piles inwards for enhanced security.

A Step-by-Step Look

Now, let’s explore the construction process:

1. Site Preparation:

Thorough investigation of the soil conditions and water levels is crucial. These findings guide the design and selection of appropriate sheet piles and construction methods.

2. Sheet Pile Installation:

Specialised equipment, like pile driving hammers or vibratory machines, drive the sheet piles into the ground until they reach the desired depth, ensuring a tight interlock between each section.

3. Bracing and Anchoring (if applicable):

For braced cofferdams, a network of steel beams and struts is strategically positioned to provide internal support. In anchored cofferdams, cables are connected to secure external anchor points, creating additional stability.

4. De-watering and Excavation:

Powerful pumps remove water from the enclosed area, creating a dry and workable environment. Once dewatered, excavation begins, carefully removing soil to create the designated space for the intended construction.

5. Construction:

Here, the project comes to life. Whether it’s a bridge, foundation, pier, or another structure, the cofferdam provides a protected area for safe and efficient construction.

6. Removal:

Once construction is complete, the cofferdam’s purpose is fulfilled. The sheet piles are extracted, often recycled for future projects, leaving behind the completed structure.

Beyond the Basics:

While the core process remains the same, specific projects might necessitate additional considerations:

  • Interlocking Systems: Different sheet pile profiles offer varying interlocking mechanisms, impacting watertightness and overall strength.
  • Environmental Concerns: Measures like silt curtains might be necessary to minimize the impact on aquatic life during construction.
  • Safety First: Stringent safety protocols are paramount, considering the heavy machinery and potential hazards involved.

The Strength of Sheet Piles: Not Just Walls

Sheet pile cofferdams represent more than just steel walls; they are vital enablers for construction in challenging environments. From bridges spanning rivers to underwater foundations, their versatility and strength pave the way for remarkable feats of engineering