China is constructing a 12-km-long high-speed train tunnel through one of the portions of its iconic Great Wall to connect Zhangjiakou city, which is due to co-host 2022 winter Olympics along with Beijing.

It took the Chinese engineers months to choreograph the best intersection point. In the end, the tunnel, deep below the Badaling section of the Great Wall, passed experts’ appraisal, State-run People’s Daily reported.

The line is designed for trains travelling up to 350 km per hour, which is expected to shorten the single-journey time from more than 3 hours to approximately one hour. The line is estimated to be completed in 2019.

The depth of the tunnel will range from four meters to 432 meters. Now, people are holding their breath on the completion of the tunnel while ensuring that the Great Wall is not damaged in the process, the Global Times reported.

Luo Duhao, chief engineer of the Beijing-Zhangjiakou High-Speed Railway Line, being built by China Railway Number 5 Engineering Group Co said the frim will employ “precision micro-blasting” technology, which has a velocity of 0.2 cm per second and is able to make the tremor weaker than the traditional firepower blasts that have a velocity of 5 cm per second.

Luo told the Global Times that the new technology will ensure that the Great Wall will not be affected by the blasts, as they will be barely felt.

“The new technology causes little damage to the geological environment, which will help protect the Great Wall,” Dai Longzhen, deputy manager of the Beijing-Zhangjiakou High-Speed Railway Line, told the Global Times.

“I myself once stood on the Great Wall and I could not feel the blast at all,” Dai added.

Zhang Xuehua, a blast expert at the construction site, told the People’s Daily that the construction of the tunnel has completed 4,500 blasts since early February this year.

In the middle of the tunnel, workers will build a spacious and well-decorated station right under the Great Wall, with a record-breaking construction space of 36,000 square meters, the Xinhua News Agency reported.

The station will be 102 meters below the surface of the Badaling Great Wall.

Originating from the Beijing Railway Station North, the Beijing-Zhangjiakou High-Speed Railway Line runs through Haidian, Changping and Yanqing districts of Beijing. The line continues northwest through Huailai and Xunhua counties in Hebei province before terminating in the city of Zhangjiakou, making for a total length of 174 km.

Built from the third century BC to the Ming Dynasty (1368-1644), the Great Wall stretches over 21,000 km. Over a four million tourists visit the Great Wall every year as it is the centre of China’s tourism campaign.

According to official statistics, about 30 per cent of a 6,200-km section of the wall built in the Ming Dynasty has disappeared, and less than 10 per cent is considered well- preserved.

The Great Wall has faced threats from both nature and humans. Earthquakes, rain, wind and other natural elements have left the wall with many decayed and crumbling bricks.