Shield tunneling
Port and
harbor technology
Urban rejuvenation
/green technology

Civil Engineering Business: Dolphin Dock (DD) construction method

The construction method for manufacturing caissons on the dolphin-type working ship


Outline of the construction

The dolphin dock construction method is a prompt and effective construction method for installing caissons for breakwaters (*), as well as underwater structures that include quay walls, seawalls, and intake of power plants by using a dolphin-type working ship. Since the equipment is settled in the mound at the seabed to be used in the dolphin dock construction method, the water area occupied for the work is small, which makes it superior with regard to safety and workability against waves generated at the time of manufacturing the caisson. Moreover, since high tranquility is ensured in the harbor, it can be used as a floating type working ship. This construction method has been adopted for more than 4,000 projects.
(*) Caisson: The concrete box composing breakwater. Patent: No. 595545


Characteristics of the
construction method

Improves work efficiency.

Since the dolphin-type working ship is settled on the seabed, it is possible to reduce the impacts of the sinking and floating movement, tilt, and shock caused by waves compared to when it is floating, thereby improving the operation rate.

Improves work environments.

The rocking movement is much less compared to when the ship is floating, which allows for a work environment equivalent to that of work on the ground.

Capable of reducing the water area occupied by work.

As the ship is settled on the seabed, installation of a mooring anchor can be minimized, which makes it suitable for small water areas.

Increases stability at the time of launch.

Because the large dolphin docks are equipped with auxiliary floats, it is also possible to control the tilt of the ship upon the launch of the caisson.

It can also be launched in white water.

Thanks to the thin platform, it can also be launched in white water.

Work in the floating state is also possible.

If the harbor is highly tranquil, it can be used as the floating type working ship.

Origin of dolphin dock
construction method

The dolphin dock construction method was developed in the renovation work for Naoetsu Port in 1965. It was named the dolphin dock construction method because the ship floats and sinks like a dolphin. It was actively used in many projects as a construction method suitable for small water areas with high waves. In 1970, the method obtained patent No. 595545 as the Method for Building Concrete Structures in Water.