South Korea is venturing into new territory with the GTX network, the "Great Train Express": Construction is currently underway for a metro line that will transport trains at speeds of up to 180 km/h. The GTX network, which will span 237 kilometers, is set to become the fastest metro line in the world and a significant solution to the traffic issues in Seoul. With the goal of drastically reducing commuting times between the metropolis and its satellite cities, this project could serve as a model for other megacities around the world.

In Seoul, most metro lines are located about 20 meters underground, while the sewage systems lie between 1 and 17 meters below the surface. The GTX network, however, takes an innovative approach: It will run 50 meters below the earth's surface, avoiding conflicts with existing infrastructure. Ultimately, the system will consist of three lines – A, B, and C – crossing Seoul along different axes.

For Line A, Herrenknecht supplied two specially configured tunnel boring machines. In the bustling downtown area of Seoul, at Seoul Station, where a beautiful colonial-era building meets a modern glass-and-steel KTX station, a Gripper TBM is being used. 

For the geological layers with sand, soil, and softer rock, such as those around the Han River, a Mixshield is employed. These machines provide tailored solutions for the various geological conditions, ensuring that tunnel construction proceeds efficiently and safely.

The two machines achieved successfull breakthrough in August 2023 and March 2024, respectively.