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Tunneling Success
The world's deepest underground high-speed railway station is under construction beneath the Great Wall
By Deng Yaqing | NO. 39 SEPTEMBER 28, 2017

The construction site of the high-speed railway station at the foot of the Badaling section of the Great Wall in Beijing's Yanqing District(XINHUA)

About one century ago, pioneering railroad engineer Jeme Tien Yow built the first railway in China connecting Beijing to Zhangjiakou in Hebei Province, which crossed the Great Wall. Today, a super construction project is underway 102 meters beneath the Great Wall—the Beijing-Zhangjiakou High-Speed Railway.

Running 174 km and dotted with 10 stations, it is the first ballasted track railway capable of carrying trains running at speeds up to 350 km per hour. The high-speed railway, which is expected to be completed by 2019, will shorten the journey time between Beijing and Zhangjiakou from more than three hours to roughly 50 minutes. When the 2022 Winter Olympic Games convene in Beijing and Zhangjiakou, the new line will serve as an important public transportation option for spectators shuttling between the two cities.

A difficult task

Running 12.01 km, the tunnel for the high-speed railway under the Badaling section of the Great Wall in north Beijing's Yanqing District passes through fault fracture zones and faces risks such as falling debris, water and mud bursts.

"Since the construction started in April 2016, we have tunneled 5,000 meters and joined the tunnel with the station, boring at an average speed of 20 meters per day," said Chen Bin, Assistant General Manager of China Railway No.5 Engineering Group, the contractor for the tunnel.

The tunnel passes under a number of world cultural heritage sites, such as the Badaling, Juyongguan and Shuiguan sections of the Great Wall. "The tunnel goes through Shifo Village and the Qinglongqiao Station of the old Beijing-Zhangjiakou railway line at depths of merely 10 and 4 meters, respectively," Chen told Beijing Review, adding that they had to develop new blasting technology to excavate the tunnel carefully in order to preserve the cultural sites.

Large-size shield tunneling machines couldn't be used, and workers could only use accurate blasting methods. The smallest explosion could only advance the tunnel by 0.8 meters.

"More than 4,500 explosions have been carried out for the tunnel's construction. We used electronic detonators to control the vibrations in batches of small explosions to reduce the impact on the inside of the hills and the Great Wall. The force exerted by each explosion is equivalent to stamping your foot on the Great Wall," said Chen.

Aside from that, the Badaling Great Wall Station on the new rail line is 102 meters beneath the Great Wall, with a total construction area covering 36,000 square meters—the size of six football fields. After completion, escalators will take passengers 62 meters to and from the surface. The station will be three-stories high, including the platforms, entrance and exit.

"Channels for outbound and inbound travelers are separated, and they will not meet inside the station. The architectural structure is unprecedented in China," said Jiang Si, head of the Project Department of the Beijing-Zhangjiakou High-Speed Railway.

"When completed, the Badaling Great Wall Station will facilitate development in Yanqing, serving the 2022 Winter Olympic Games and the Badaling scenic area," said Lu Gang, chief designer of the project.

"The burrowing work is quite complicated, because the station has to contain 78 caverns and lots of intersections. The main span of the tunnel reaches 32.7 meters, the widest span of a railway tunnel in China," said Zhao Yong, an engineer working on the project.

Safety first

To reinforce the tunnel, workers first seal up the walls with a layer of mixed cement, then embed bundles of steel bars several meters into the wall, which are called pre-stressed anchor cables and serve as huge screw spikes. "The depth and density of the cables vary with tunnel span," Zhao said.

In addition, workers have to pump at least 19,000 cubic meters of underground water out of the tunnel every day, which equals to the volume of about 10 swimming pools with eight lanes.

To secure the safety of passengers, the inclined shafts which are used to transport construction materials, waste soil and debris will be converted into permanent rescue channels.

"By now, the construction is 40 percent complete. It will only take 20 minutes to travel from downtown Beijing to Badaling when it is completed," said Chen.

As a matter of fact, during the 13th Five-Year Plan (2016-20) period, China has made great progress in terms of high-speed railway construction, with a total operating length exceeding 22,000 km, accounting for over 60 percent of the world's total.

"The length is likely to reach 45,000 km by 2030, when the national high-speed railway network consisting of eight vertical and eight horizontal lines is completed," said Liu Xiaoguang, Director of the Railway Engineering Research Institute of the China Academy of Railway Sciences, at a forum on railroad bridge construction in Beijing on September 5.

Copyedited by Bryan Michael Galvan

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