[ The Geumbit Noeulgyo Bridge underpass offers a wider sense of space by constructing curved walls ]

Sejong Special Self-Governing City in South Korea that was first developed by putting together the natural environment and systematic urban planning initiative. Sejong City, which marks its 10th anniversary this year, is about three-quarters (464㎢) of the capital Seoul, more than twice the area of the tier one to tier three new towns developed in the region of Gyeonggi Province. Sejong is largely divided into ‘administrative-centered complex city’ where more than 70% of the population resides, and its vicinity such as Jeonui-myeon, Jeondong-myeon, and Jochiwon-eup. "Administrative-centered complex city" is a key district, where numerous administrative agencies, government-funded research institutes, apartments, schools, and commercial facilities are concentrated, and is characterized by the design of a ‘double-circular’ structure with a donut-shaped transportation network placed in two layers, along the green spaces at the center. Currently, a wide range of infrastructure projects to build expressway and outer ring roads connecting the Living Zones one to six are under step-by-step implementation. Soon, a new road is scheduled to open to make the lives of Sejong citizens more convenient. 

What is striking about the ‘Geumbit Noeulgyo Bridge and Outer Ring Road Living Zone 5’ is that the 3.6km section excluding the bridge was designed as an underpass. The underpass which allows vehicles to pass without waiting for signals, not only helps alleviate traffic circulation, but also make ground spaces greener, resulted in much higher satisfaction for both drivers and pedestrians. Usually, an underpass feels dark and stuffy when you drive for a long time. But the underpass built by Hyundai E&C offers greater sense of illumination and openness. This is thanks to the ‘curved wall’ embedded across the entire section for first time in Korea. The underpass seems to provide more room for air because the spaces seem larger compared to the flat-wall type. It was laborious process, to construct by dividing forms and sections into exclusive molds, but definitely contributed greatly to easing a sense of closure.

Brighter and pleasant underpass, with permeating sunlight!

[ A sunken shaft is installed on the sound-proof tunnel (right) underpass before the entrance of the main underpass (left), illuminating overall environment. ]

Another key to providing a pleasant environment for drivers is ‘sunken shaft’. The sunken shaft, which gives the underground space a sense of lighting and openness, is mainly found in buildings, and Hyundai E&C placed three sunken shafts on the side of the underpass so that natural ground sunlight can naturally permeate. A sunken shaft can also be used as a space for evacuation in case of an emergency. That’s not all! Numerous disaster prevention facilities are essential. In the case of underground structures over 3km, evaluation and disaster prevention grade 1 or higher should be applied to the design, and the Outer Ring Road Living Zone 5 is also equipped with facilities certified with evacuation and disaster prevention grade 1 or higher to better respond to potential case of emergencies including fire. In particular, the internal air quality of the underpass is measured in real time, and in case of deterioration, fresh air is blown into the entire section from duct slabs installed in empty spaces of the ceiling. 

There is a two-story tunnel traversing the city center?!

[ Point connecting 2 tunnels (Dasom tunnel and ramp tunnel). When going up the ramp tunnel, ‘National Route no. 96’ is accessible ]

On the ‘Geumbit Noeulgyo Bridge and Outer Ring Road Living Zone 5’, a special instrument is hidden to resolve habitual congestion while communiting. That is, the ‘two-story tunnel’, which is rarely found on other roadways. The section where the tunnel is located is the intersection joining the National Route no. 96. It is a habitual congestion zone for commuting as drivers can go to Namcheongju, Sejong Government Complex, Osong, and Daejeon, from the east to west. Hyundai E&C built Dasom tunnel (460m) at the lower segment and excavated sequentially a ramp tunnel on top of it (290m). For tunnel excavation was used the New Australian Tunneling Method (NATM) method of drilling a hole in a solid rock, mounting gunpowder, and then triggering an explosion. Despite the fact that the distance between the upper and lower tunnels is only 20 meters, the tunnel was successfully excavated based on Hyundai E&C’s precise construction technology. In addition, since Mount Chuldongsan (148.9m above sea level), registered cultural heritage of General Lim Nan-soo's tomb, and the semi-conductor factory are located near the tunnel, it was crucial to focus efforts on management of blasting vibration. 

Hyundai E&C applied 'Integrated Triangular Core Shield Method' to ensure construction safety. This engineering method involves placing entrance and exit tunnels in a triangle formation at the upper part of the two lower tunnels (ascending and descending lines), so that the force of the fault is evenly distributed and supported by the three tunnels. Hyundai E&C carefully installed and reinforced steel pipes on the side walls of each tunnel and made every effort to ensure safety through additional reinforcement work on the fault zone.

Geumbit Noeulgyo Bridge embodying waters of Geumgang River

[ Geumbit Noeulgyo Bridge is the longest hybrid twin arch bridge in Korea, with lower pier and upper arch creating soft structural aesthetics ]

The grand finale of the site is decorated with ‘Geumbit Noeulgyo Bridge’, which perfectly blends in with the surrounding environment. By fully leveraging the benefits of ‘concrete bridge’ and ‘steel bridge’*, the lower segment was constructed as a concrete bridge and the upper segment was as a steel bridge to maximize durability. The span (between bridge tower to tower) is 175 meters, making it the longest among hybrid twin arch bridges in Korea.

*Steel bridge: A bridge which uses steel materials based on steel processed as construction material, to build key components of the bridge as a material for construction, etc.

The design of the bridge is inspired by images of water streaks and the golden sunset of Geumgang River. It presents a beautifully curved aesthetics, in which the lower piers (column supporting the legs) and the upper arch are naturally connected like flowing water. While the piers commonly seen are constructed by placing the top plate on a vertically raised pillar, the piers of the Geumbit Noeulgyo Bridge are in the form of a ‘reverse arch’ that inverts the top and bottom of the arch. There are few cases of construction of reverse arch piers in Korea, and construction itself is very challenging. The amount of puncheon (a post temporarily supporting the weights during construction) steels used to withstand the massive concrete load is 10,000 tons, equivalent to the weight of the Eiffel Tower. It took Hyundai E&C 8 to 10 months to complete one pier using the Free Cantilever Method (FCM)*. It also devoted a lot of efforts by placing 150 workers a day on the construction site, which amounted to a total of 100,000 workers during the 30-month period.

*Free Cantilever Method (FCM): Constructing sequentially using mobile temporary trusses to balance the left and right sides of the superstructure (segment)

Core infrastructure in five living zones, embodying expectations of local residents

Currently, the Geumbit Noeulgyo Bridge and Outer Ring Road Living Zone 5 site is in its final phase, working on  power construction and lane painting, awaiting its official opening early next year. Various amenities an auto camping site and a water playground are built at the lower segment of the bridge. They will be transformed into a happy outdoor space for citizens, perfectly blending in with Chungcheong Province’s largest Hapgang camping site located nearby. Along with the opening, it not only will improve accessibility between Sejong, Cheongju, and Osong, but also help resolve chronic traffic congestion. The site manager Lee Kwang-chul explains, "We have experienced many crises such as Covid-19 and disrupted supply and demand for materials over the past five years, and yet thanks to the employees' concerted efforts, we were able to carry out the construction without difficulty," adding, “I hope this project will not only improve the quality of life of local residents, but also set a good precedent for the civil engineering projects that Hyundai E&C will lead in the future.”

▼ Watch the video of Hyundai E&C’s Geumbit Noeulgyo Bridge