06/10/2026
HOW ENGINEERS BUILD IN THE MIDDLE OF WATER
What do you do when the foundation needs to be built underwater—but the workers need a dry excavation?
The answer is often a cofferdam: a temporary watertight or low-permeability enclosure that allows engineers to isolate an excavation, control water, and create a safer working area.
Different site conditions require different cofferdam systems:
🔹 Earth or Rock-Fill Cofferdams
Used mainly in relatively shallow water and lower-flow conditions where locally available fill can provide economical temporary containment.
🔹 Sheet-Pile Cofferdams
Interlocking steel sheet piles are driven into the ground to form a continuous enclosure. They are widely used for bridge piers, marine works, and excavations where groundwater and soil conditions must be controlled.
🔹 Cellular Cofferdams
Large interconnected steel cells are filled with granular material, creating a massive and stable temporary structure suitable for demanding water environments.
⚙️ The engineering challenge goes beyond simply stopping water.
Engineers must consider:
• Water depth and velocity
• Soil and foundation conditions
• Hydrostatic and seepage pressures
• Excavation stability
• Pumping and dewatering requirements
• Structural stability and deformation
• Construction sequence and environmental constraints
A successful cofferdam is a carefully engineered balance between hydraulics, geotechnical engineering, structural stability, and construction methodology.
🌉 From bridge foundations to dams and marine infrastructure, temporary works often determine whether a complex project can be built safely and efficiently.
