China is building a high-speed railway station under the country's most popular section of the Great Wall outside Beijing.

The Badaling Terminal, schemed to open by the end of 2019, will occupy 36,000 square meters. The gigantic labyrinth, some 100 meters underground, is the deepest and largest high-speed train station in the world.

The tunnel spans 12.01 kilometers from Beijing’s Changping District to Yanqing District and is an important section of the Beijing-Zhangjiakou High-Speed Railway. The tunnel ranges from four to 432 meters underground.

Chinese engineers used small explosions to dig the tunnel. The controlled explosions reduce the impact so as to protect the Great Wall and carve out tunnel.

The underground construction is the country's most complicated, because the station has to contain 78 caverns and lots of intersections, said Chen Bin, a commander-in-chief of the project.

The Great Wall at Badaling

According to an initial plan, workers could excavate the tunnel 6 to 8 meters a day, but the tough rock meant they could dig only about 2 meters a day.

Another problem in the tunneling is the underground water. Every day, workers have to pump out no less than 19,000 cubic meters of water, which equals about 10 swimming pools.

An estimated 4,500 controlled explosions have been carried out, according to a construction worker surnamed Zhang. Zhang said he once stood on the Great Wall and did not feel the force of the explosion.

The underground station will have three floors and separate levels for arriving and departing passengers. Two escalators with vertical heights of 62 meters, the highest in the country, will also be installed in the station.

The Beijing-Zhangjiakou High-Speed Railway is an important project for the 2022 Winter Olympic Games.