Korean highway links Seoul to the sea 27 Jul 2017

The new 72km long Dongsea highway in South Korea to link the capital Seoul to the east coast city of Yangyang will cut the current fastest route via Chuncheon of more than two hours on a 78.5km long heavily congested expressway built in 2009, to 90 minutes (Fig 1).

Alignment of the new route to the sea

Some 73% of the new Dongsea highway runs through 35 tunnels and across 58 viaducts to navigate the mountainous terrain. The longest tunnel on the new route is the 11km long Inje Tunnel, which is also the longest highway tunnel in the nation and the 11th longest in the world.

Construction of the long tunnel was awarded for a contract value of Korean Won 534 trillion (US$510 million) to a consortium of five Korean companies led by Daewoo E&C with a 50% stake. Drill+blast NATM excavation of the twin tube tunnel started in 2011 and progressed from both portals and in both directions from a 1.4km long mid-point adit to achieve final breakthrough on the twin 11km long tubes within two and half years. The adit is a permanent structure that will be used during operation for ventilation and as an access for fire-fighting and emergency vehicles. Another two vertical shafts add to the ventilation of the twin tube tunnel

A priority during construction was environmental protection of the Baekdu Daegan, a mountain range and watershed crest that runs most of the length of the Korean Peninsula. Deputy General Manager Chung Yeon Hoon explained that the tunnel alignment was optimized based on geological features and passes a maximum 556m below the mountain range and beneath a local river.

The 11km long Inje twin-tube tunnel is longest of 35 tunnels on the new route

“As well as being the longest highway tunnel in the country, the tunnel is designed to be the safest in Korea,” said Lee Yong Woo, General Manager of Daewoo E&C and Project Manager of the construction site. “One of the outstanding features is design and construction of six vehicular cross passages. Emergency vehicles are stationed on standby in these connecting passages and large vehicles can be directed through the passages and back out of the tunnel in the parallel tube in the event of an in-tunnel emergency. An additional 20 cross passages will accommodate passenger cars in the event of emergencies.”

Final lining at a vehicle cross passage point

Lee Yong-woo, Project Manager of the Inje Tunnel

Firefighting vehicles will use the central adit to access emergencies more quickly and the adit will also provide temporary shelter for motorists if necessary. Another 37 cross passages fitted with double doors will protect passages should evacuation of cars be needed in an in-tunnel emergency.

In combination with emergency response traffic management, the tunnel is fitted with deluge sprinklers along its full twin-tube length. There are also 10 stations of foam generating equipment for addressing fires caused by petroleum vehicles and large-scale fire accidents. Six automatic dampers and high-pressure precision sprinkler systems are in place to prevent secondary car pile-up fires.

The tunnel is also fitted with longitudinal ventilation fans plus freeze protection and remotely-controlled fog detection systems for added safety at the portals. To maintain the interest, attention and concentration of motorists as they travel through the long highway tubes, artistic landscape lighting impressions are projected onto the crown at four locations.

As well as creating a faster route between Seoul and the east coast, the new Dongsea highway is expected to boost economic growth in northern Gangwon Province and regions across Mt Seorak and along the eastern seaboard.