Seoul's super-fast subway is taking shape 50 meters below the ground. Photo: Asia Times/Andrew Salmon

South Korea is breaking new ground literally and figuratively: Work is underway on a subway line on which trains will run at up to 180km/h.

Seoul’s GTX (“Great Train Express”) network is set to be the world’s fastest underground rail line when it begins operations under the capital’s streets in three years. It aims to hyper-accelerate passengers across the vast sprawl of Seoul and slash commuting times between the metropolis and its surrounding satellite cities.

Project visionaries call it the beginning of a transport revolution. And indeed GTX could provide a congestion-smashing model for mega cities around Asia – and across the world.

But to be successful, it has to overcome a range of engineering challenges, deal with protests related to underground real estate ownership and overcome fears over buried cultural properties uncovered during construction.

South Korea’s bullet train, the KTX, is going underground in a bid to overcome urban congestion. Photo: Asia Times/Andrew Salmon

Seoul’s siren lure

“As long as you reach Seoul, you can achieve anything you want,” is a traditional saying that showcases the significance of their capital to Koreans. But it is as much a curse as a blessing.

For decades, multiple administrations have undertaken decentralization initiatives, included shifting major ministries and governments agencies outside Seoul and even raising an entirely administrative city, Sejong City, south of the capital, from scratch.

Yet Seoul remains one of the most centralized conurbations on earth.

It is home to some 10 million people, but when its surrounding cites – notably the port/industrial city of Inchon to the west, the electronics industry hub of Suwon to its south and the dormitory town of Ilsan to the north – are added, the population of the Great Seoul Metropolitan Area leaps to 25 million people, fully half the national population.

To move these millions, Seoul offers a modern, economical and extensive subway system, dedicated bus lanes on its major road arteries and even inner-city expressways along the banks of the Han River. Yet, the compression of so many people into this shared space has had dire results.

The average daily commute for Seoulites is 133 minutes, compared with 28 minutes in the OECD, Jang Chang-seog, Capital Region Express Rail Director of the Ministry of Land Infrastructure and Transportation (MOLIT) said in a presentation last week.  

Seoul’s subway conveys some 10.69 million passengers per day, Jang said. As it dates back only to the 1970s, its equipment is modern and efficient, but though 353km long, is weighed down with more than 700 stations on its nine inner city and ancillary lines. That means stop-start trains that never get up a head of steam.

The vast city of Seoul has superb public transport – but dire commutes. A new solution is needed. Photo: Robert Koehler

Enter the GTX

GTX is the opposite concept.

Using similar technologies to those deployed in the above-ground “KTX” (“Korea Train Express”) bullet trains, GTX will race along at an average 100km/h, revving up to a maximum of 180km/h. GTX will boast 237km of line but only 33 stations.

However, GTX will connect to strategic hubs, such as downtown’s Seoul Station. From there, passengers will be conveyed via high-speed escalators into the subway net for “last mile” transit.  

While most of Seoul’s subway lines are about 20m below ground, and sewers are between one and 17 meters below the surface, GTX avoids conflicts by being 50m below ground.

Following a feasibility study in 2014, the project was announced in 2017, and work began on the first line in December 2018. Eventually, GTX will comprise three lines –  A, B, and C – crossing Seoul on different axes.

The ambition of the project, which is more than five times longer than the Channel Tunnel, is massive. GTX should slash commuting times in the metropolitan area by 71%, Jang said.

That means someone living in the dormitory town of Ilsan – a middle-class, new city noted for its lake park and its KINTEX Convention Center – will be able to reach Seoul Station within 20 minutes rather than 40. Or, a resident of Incheon’s high-tech, smart city of Songdo will be able to reach Seoul in 23, rather than 57 minutes.

The first of three project lines, GTX Line A, is 83km long with 10 stations, running roughly northwest to south, from Paju to Dongtan. Construction started in 2019 and completion is expected in 2023. Anticipated cost is 4.8 trillion won ($4.2 billion). By 2023 or early 2024, the line will be carrying more than 262,000 passengers per day on 141 eight-car trains.

Underground is where the new action is for high-speed rail. Photo: Tom Coyner

The second line is 80km with 13 stations running roughly east-west from Maseok to Songdo. Construction should start in 2023, with a cost of 5.7 trillion. The third line is 74.8km with 10 stations running roughly northeast to south, Deokjeong to Suwon. Construction should start in 2022, with a budget of 4.3 trillion.

GTX’s financial format is a public-private partnership that will hand over the asset to the government on completion. Companies engaged at present include Hyundai Rotem, which is supplying trains, and Daewoo Engineering and Construction, which is engaged in tunneling.

Jang noted that his team had “researched a lot of cases in other countries,” and in terms of both speed and scale, GTX looks to be the world leader in underground high-speed rail transit.

London’s upcoming east-west Crossrail runs for 117km  at up to 140km/h. France’s ongoing RER is longer than GTX in total, but only 76.5km of its track  is underground and it, too, boasts a maximum of 140km/h.

The three GTX lines will not only link Seoul with satellite cities, they will accelerate cross-city commuters. Image: MOLIT

Going underground

The scale and promise of GTX is impossible to grasp at ground level.

In parts of Seoul, small construction sites are visible behind gray hoardings. These are emergency access roads being built into the tunnel. And in downtown’s bustling Seoul Station, marked by both a fine colonial-era red brick building and a glass-and-steel KTX station, a GTX station is being built below the converging subway platforms.

To appreciate that project’s scale, one has to go deep. One site to do that is the GTX Line A tunnel being dug at KINTEX, a giant exhibition center in the satellite city of Ilsan, an hour’s drive from central Seoul.

The site is only about 100 square meters. Inside, a large sign warns: “Nobody is a veteran when it comes to safety!” The main facility is a cage elevator large enough to convey vehicles up and down. On Monday, Seoul-based foreign reporters were welcomed to the site. After donning hard hats, the group entered the cage and descended.

Elevator and air shaft at the GTX site in KINTEX, Ilsan, South Korea. Photo: Asia Times/Andrew Salmon

The tunnel itself is a floodlit, concrete-lined arch. Tracks have not yet been laid, and no trains are in evidence, but pipes and cables snake along the floor, and muddy excavators are parked along the tunnel walls. Though water drips constantly – the tunnel is below Ilsan’s water table – the air is surprisingly cool and fresh.

The tunnel’s terminus is an earthen disc with three holes drilled into it for placement of explosives. The site’s engineering supervisor, Park Rak-soo, explained the process.

Explosive charges are placed in the holes. After the tunnel has been evacuated, they are detonated sequentially or all together. Park, who has been tunneling for 35 years, says the depth of the excavations is challenging. Most of his experience has been in open-cut excavations.

“Safety is the issue,” he said, citing the high-rise buildings on the surface. A 20m steel hoop – an “umbrella arch” – has been secured over the disc of earth to ensure there is no tunnel collapse when the explosives are detonated. Explosives, counterintuitively, are safe and gradualist. Park and his team are advancing their section of the tunnel about three meters per day.

In other sections of the tunnel, faster excavations will be undertaken by unleashing 100m-long Tunnel Boring Machines, or TBMs. These monsters are being constructed to GTX specs in China. They can advance tunnels around 15 meters per day.

Two types will be used to deal with different characteristics of Seoul’s geology, explained Kim Chang-yong, who heads the Future Infrastructure Center of the Korean Institute of Civil Engineering and Technology.

A “Gripper” TBM,  which clings to the sides of the tunnel, will be used in areas of hard rock, which define most of Seoul’s underground. A “Shield” TBM will be used in areas of sand, soil and soft rock, such as the area in the vicinity of Seoul’s Han River. Both include conveyer belts that carry detritus back into the tunnel for disposal.

Given the depth of the tunnel, there are no underground obstacles such as piping, cables or subway tunnels to evade, except for geothermal power facilities. As these are all modern, they have been thoroughly mapped, Kim said.

The obstacles facing GTX have, thus far, have been above ground.

A South Korean engineer points out the terrain-chewing features on this diagram of the business end of a Tunnel Boring Machine. Photo: Tom Coyner

Teething troubles

South Korea has an unusual aspect to its property law, Kim explained, in which property rights extend to 40m below the ground. Even though GTX is 50m underground, there have still been complaints from residents along its route about the possibility of vibrations from the system undermining their properties.

Subways lines have not faced these complaints, Kim said, as most are build under roads, and roads are government owned. That is not the case for the GTX.

“Technically, it’s all feasible,” Kim said, but – echoing the complaints of entrepreneurs and innovators in other areas of the economy – noted that regulatory issues are the holdup.

“Government has the responsibility to tell the citizens what is going on, so there have been public hearings,” he said. “But residents are not well aware of this, and there have been protests.”

In a city in which real estate valuations are one route to riches – and therefore very politically sensitive – this has led to demands for compensation.

However, a revision to related laws is currently pending at the National Assembly. That, Kim hopes, will clear this logjam.

But another hitch has also been hit. At the end of 2020, GTX excavations under central Seoul’s Gwanghwamun area uncovered buried cultural artifacts, leading the Chosun Ilbo, Korea’s leading newspaper, to dub GTX, “the unlucky line.”

It is unclear, at time of writing, whether, or for how long, this will delay work.

Given its potential to cure so many commuter frustrations, the importance of the GTX project extends beyond Korea, Kim insisted.

“This is a really rare experiment,” Kim said. “Other countries will be paying attention to the technologies we are using.”