Engineering and building under water — how is it done, and the modern use of Cofferdams

On the surface, pun intended, building underwater is “simple.” Engineers erect prefabricated walls or piles and pump water out to create a dry working area within the walls known as a cofferdam.

However, today with more and more underwater construction, on a massive scale, planning and engineering are increasingly challenging. As populations grow, the need for underwater tunnels and harbor improvements make versatile cofferdams essential. With immense water pressure pressing from all sides, the safety and effectiveness of cofferdam technology have been reinvented and innovated to suit increasing demands.

 

Engineered Design Insider Building a cofferdam in harborOil Gas Automotive Aerospace Industry Magazine
Building a Cofferdam in a harbor.

 

A Brief History of Cofferdams

Cofferdams can be traced back to the Persian Empire and have stood the test of time due to their effectiveness and the lack of alternatives when it comes to underwater construction. The original cofferdams used by Persians were constructed by piling earth around the area to be constructed and bucketing water out to create a dry work area. Even though this process was tedious and risky, it got the job done. The earth walls were removed once the construction was completed.

Cofferdam engineering was advanced further by the Romans, where woodpiles were used instead of earth. The woodpiles were driven into the waterbed to create a wall around the area to be constructed. In the early 1900s, the same technique was adopted and reinvented by German engineers to create the modern steel cofferdams by replacing woodpiles with steel sheets with the first design utilizing interlocking U shaped steep. This innovative cofferdam design is effective in controlling water-flow and is still used by modern underwater engineers to build cofferdams with minor changes in the interlocking design and technology.

 

Engineered Design Insider Building an underwater tunnelOil Gas Automotive Aerospace Industry Magazine
The construction work of the University of Macau Hengqin campus including the library and central teaching buildings in Macau. The work on first phase includes of the seabed tunnel connecting Macau and the campus also commenced with the construction of a cofferdam, which will provide a watertight enclosure within the river that will be pumped dry to provide a dry work environment below the waterline. Preliminary design and environment assessment concerning the seabed tunnel have already been completed and the project has also passed the experts’ examination. The Secretary for Transport and Public Works of Macau has stated that the campus construction is progressing on schedule and the completion of construction is scheduled within a period three years.

 

Modern Cofferdams

The process of creating cofferdams goes beyond driving steel sheets into the ground to create an enclosure; it requires geotechnical expertise. For one, the structure must provide not only a dry surface for construction but also guarantee the safety of engineers and constructors working inside the cofferdam from collapse. In terms of geotechnical engineering, the steel piles should be driven down deep enough to ensure that water does not seep through but not too deep because it can be difficult to remove once the construction is completed.

The cellular, braced, single-walled, and double-walled are the four types of cofferdams commonly used to create a dry work area for construction. For each type, engineers determine the depth at which the wall should be driven into the ground depending on soil type and water table to ensure that water does not seep up through the ground into the enclosed dry working area. Having a dry work area is particularly important in the construction of support piers for bridges because these structures are built using concrete that requires perfectly dry conditions to cure evenly and thoroughly. Uncured or unevenly-cured concrete piers cannot support immense weight, which increases the risk of collapse. Apart from support piers for bridges, engineers can build cofferdams to act as drydock for large ships that need to be repaired but cannot be lifted out of the water due to size.

 

Engineered Design Insider CofferdamOil Gas Automotive Aerospace Industry Magazine

 

Cofferdam safety

In terms of cofferdam safety, engineers calculate the most appropriate height of the piles taking changes in the water levels due to factors such as tides, flood, and so on to keep water out. Erecting a very tall cofferdam wall not only increases instability but will also make it harder for the cranes to offload construction materials from a floating staging site into the cofferdam. The steel sheets are driven into the waterbed to attain the desired depth, height, and shape; then, water is pumped out to create a cofferdam using powerful water pumps. In case the cofferdam begins to flood during construction, a series of primary and backup pumps on standby kicks into overdrive to provide a window for the crew to be evacuated from the cofferdam.

After completion of the project, the walls are pulled out using powerful cranes. The price tag for creating cofferdams is enormous, and they are only used when there are no other viable construction alternatives.

Did you miss this?

Other Popular Stories

  • Swimming Robot to Examine Damage from Japan’s Nuclear Reactor
  • Scientists Develop Plastic-Eating Enzyme
  • Supercapacitors Increase Performance and Longevity, Charge in Minutes
  • Continued strength in manufacturing in November: RBC
  • Eleventh hour intervention by Marchionne secured Fiat Chrysler deal
  • Scientists Develop Sustainable Battery Using Tree Bark Tannins
  • New MRO operation rising in former Aveos plant
  • Solar-powered nanoheaters offer solution for off-grid medical sterilization
  • Manufacturing grew in August; oil industry to lose $2.1 billion in 2015
  • Global car sales will set new record in 2014: Scotiabank
  • Canada's prosperity at risk from disruption, lack of skilled workforce: reports
  • Cap and trade law passes in Ontario, carbon pricing set to begin
  • Diesel emissions fallout continues: US. to sue Chrysler Fiat if talks fail
  • Canadian oil production up; producers turning to railways for shipment
  • Robocop becomes real-world: robot law enforcement in Dubai may bring Robocop to a neighborhood near you
  • Tesla Roadster not only zero-to-sixty in 1.9 seconds — the next iteration may actually fly, says Elon Musk, CEO
  • Wind projects going ahead in Quebec, public not necessarily on board
  • Research: What is the temperature effect on battery backs in Electric Vehicles: charging up to 3 times longer in coldest temperatures
  • Canada risks losing out in renewable energy revolution
  • General Motors Planning Autonomous Vehicles Sans Controls
Scroll to Top