DL E&C has completed the installation of the final caisson, a key structural element in the construction of Ulleung Airport, marking a significant milestone in laying the foundation for the runway.
On May 8, DL E&C announced that all 30 caissons — the large concrete structures used as foundations for port walls and breakwaters — had been successfully installed. This represents approximately three years since the first caisson was installed in May 2022. The completion of this work signifies the end of preliminary foundation construction necessary for the runway development.
Ulleung Airport is notable for being South Korea’s first airport built on an island without a land connection. To overcome the limited flat terrain suitable for a runway on Ulleungdo, DL E&C applied the ‘caisson method’ for the first time in Korea. This technique involves sinking caissons into the sea, creating a barrier against seawater, and then filling the interior to form the runway site.
Ulleungdo, a volcanic island with depths reaching around 30 meters, required the use of some of the largest caissons in the country. The largest caisson measures 28 meters in height, 32 meters in width, and 38 meters in length, weighing up to 16,400 tons — comparable to over 10,000 mid-sized cars.
To mitigate the impact of strong coastal currents, DL E&C developed and employed a ‘wave-dispersing caisson,’ inspired by a honeycomb structure. This lattice design disperses wave energy, increasing stability, while its curved shape is engineered to withstand maximum wave heights of 22.6 meters, which could occur once in 200 years.
The caissons, manufactured in Pohang’s Youngilman area, were transported to Ulleung Island via a specialized vessel called IPCCV (Individual Pushing Caisson Carrier Vehicle). The IPCCV is equipped with 96 hydraulic jacks capable of lifting up to 250 tons and moves along installed rails on the seabed.
Transporting the caissons involved multiple trips over approximately 210 kilometers from Pohang to Ulleung, with each caisson being towed by barge. The total transportation distance reached about 6,300 kilometers — roughly equivalent to eight round-trips between Seoul and Busan. Transportation was challenging, as sea conditions required waves lower than 1.5 meters and stable conditions for at least five days, necessitating careful scheduling with an average of only 10-15 operational days per month.
Once installed, the caissons were anchored in position, and approximately 60,000 tons of gravel were used to support the 16,400-ton structures. Due to the varying size and shape of the gravel, divers manually filled the gaps to ensure precise positioning and stability.
Ulleung Airport is currently under construction on an area of approximately 434,455 square meters near Sado Port, with a total project cost of around 607.3 billion KRW. Managed as a turnkey project — covering design, material procurement, and construction — DL E&C has been progressing since breaking ground in July 2020, with the project now at 61% completion. The final stages include filling major airport infrastructure and constructing the runway, with plans to open the airport by 2028.
Once completed, travel time from Seoul to Ulleung Island will be drastically reduced from about seven hours to roughly one hour.
A DL E&C spokesperson stated, “Ulleung Airport is being built under challenging natural conditions, such as strong waves and deep waters, requiring advanced technology and utmost stability. Our entire team is committed to completing this project safely and to the highest standards.”
