The Zhengzhou-Wanzhou High-Speed Railway starts in Zhengzhou, Henan, passes through Xiangyang, Shennongjia, Yichang, and Enshi in Hubei, and ends in Wanzhou, Chongqing.
Recently, after four years, the Gaojiaping Tunnel, the most karst-developed and high-risk tunnel on the entire Zhengzhou-Wanzhou High-Speed Railway, was successfully holed through. The tunnel is 5,506 meters long and is located in Nanzhang County, Xiangyang. It is a demonstration project for mechanized supporting construction and intelligent construction of China's high-speed railway tunnels, marking a new step forward in China's intelligent and mechanized tunnel construction. On the same day, a reporter from Hubei Daily's all-media team walked into Nanzhang County to explore the story behind the tunnel breakthrough.
Building over 5,000 meters of drainage tunnel for the tunnel
On April 12, the reporter walked to the breakthrough point and saw two dark tunnel portals, one on the left and one on the right, on the right side of the main tunnel. "The left tunnel is the drainage tunnel, and the right tunnel is the bypass adit," said Liu Jiang, deputy commander of the 5th bid section project department of the Hubei section of the Zhengzhou-Wanzhou High-Speed Railway of China Railway 11th Bureau. To ensure tunnel construction and normal railway operation later, the drainage tunnel and bypass adit built on one side of the main tunnel total more than 5,600 meters, longer than the main tunnel itself. "Once water flows down from the karst cave above the main tunnel, it will be discharged through the bypass adit and the tunnel drainage tunnel."
As one of the most karst-developed and high-risk tunnels on the entire Zhengzhou-Wanzhou High-Speed Railway, the Gaojiaping Tunnel has more than 30 large and small karst caves alone and is prone to water and mud inrushes and other dangerous situations. Construction is difficult, and it is a key and difficult control project on the entire line. The most difficult one was a karst cave with a diameter of 15 meters and a height of nearly 300 meters.
Liu Jiang said that on September 19, 2020, when the exit of the Gaojiaping Tunnel had been excavated to 2.5 kilometers, a mud inrush of about 25,000 cubic meters occurred, covering the working face for nearly 100 meters and interrupting construction for a time. Exploration found that a large karst cave with a diameter of 15 meters and a height of nearly 300 meters intersected the main tunnel vertically. The project department invited experts from China State Railway Group, Wuhan-Jiujiang Passenger Dedicated Line Hubei Company, and nationally renowned tunnel experts to conduct on-site "consultations" many times and decided to excavate a bypass adit and a drainage tunnel on the right side parallel to the main tunnel to release ground stress and drain water.
During the Spring Festival, more than 200 construction workers gave up the chance to go home for the holiday and worked overtime on 18 working faces to excavate the drainage tunnel, which was holed through in January 2021. The tunnel took only more than three months to complete a drainage tunnel that would normally take two years to build, setting a construction record for drainage tunnels. "The drainage tunnel not only played a role in draining water for construction, but also, during later train operation, can guide the accumulated water in the karst cave through this drainage tunnel to ensure the safety of the main tunnel and train operations," Liu Jiang said.
Full-process mechanized and intelligent construction
The Gaojiaping Tunnel is one of the most complex high-risk karst tunnels in China, and its construction process created a demonstration project for mechanized supporting construction and intelligent construction of China's high-speed railway tunnels.
"For weak surrounding rock, stepped construction was used in the past, which was slow and had high safety risks. Under the leadership of Wuhan-Jiujiang Passenger Dedicated Line Hubei Company, we achieved mechanized and intelligent construction of the full cross-section, all surrounding rock grades, and all processes for the first time in the Gaojiaping Tunnel," said Li Jianhua, commander of the project department. The project department used advanced geological forecasting to pre-explore ahead of the tunnel, combined with the measurement-while-drilling system of intelligent three-arm rock drilling jumbos, digital imaging technology for the surrounding rock at the tunnel face, and a cloud platform data processing center to automatically analyze and judge the surrounding rock grade. The system also automatically recommends support schemes, greatly reducing manual judgment errors.
Moreover, the degree of mechanization in construction was greatly improved. In the past, drilling at the tunnel face and loading explosives relied entirely on manual labor, which was time-consuming and risky. Intelligent three-arm rock drilling jumbos can automatically drill in 30 seconds, saving more time than manual drilling. In the past, explosives were loaded manually; the Gaojiaping Tunnel used the most advanced intelligent charging equipment in China instead, making explosive loading more precise, and used pump injection to press the explosives into the blast holes. "A tunnel face that used to require 50 to 60 workers can now be completed with only 10 people. Mechanized and intelligent construction not only ensured construction safety and reduced the number of construction workers but also greatly improved work efficiency," Li Jianhua said.
Tunnel construction also used new equipment and new tooling such as multifunctional arch installation jumbos, wet spraying manipulators, and self-propelled invert trestles, achieving mechanization of the entire excavation process. "The efficient breakthrough of this tunnel has provided rich experience for more intelligent and mechanized tunnel excavation in China and laid a solid foundation for the opening of the entire line," Li Jianhua said proudly.
After the Zhengzhou-Wanzhou High-Speed Railway opens to traffic, Xiangyang to Chongqing and Zhengzhou can both be reached within 2 hours. It will also connect with the Beijing-Guangzhou, Lanzhou-Lianyungang, and Lanzhou-Chongqing railways, becoming a fast high-speed corridor connecting the Central Plains, Central China, and Southwest China. It is of great significance for facilitating travel for people along the line, promoting the development of tourism resources in the Three Gorges, and advancing the construction of the Yangtze River Economic Belt.