By Qiu Chaoyi, People’s Daily
The world’s longest highway spiral tunnel is currently under construction in Jiaoding Mountain of central China’s Henan province.
The world’s longest Hankou tunnel of 27km constructed by the Road and Bridge Group under China State Construction Engineering Corporation (CSCEC) winds through rocks.
On a straight grid, the tunnel should be a stretch of just 7km, but the windy and tortuous bends stretch it almost four times longer, with a highly challenging elevation.
The tunnel project is an extremely difficult task. “Construction teams arrived here 10 years ago, and many refused to contract the project after field investigation,” said Wang Xiaodong, an employee with the CSCEC Road and Bridge Group Co., Ltd.
Ma Zhanchao, who is in charge of the tunnel project, introduced that the tunnel has an elevation difference of 109 meters between its entrance and exit. Due to the elevation, the tunnel has to be built in spiral, and the curve radius is only 700 meters at the minimum, which could easily lead to insufficient oxygen and deflection.
In addition, construction workers have to operate on nearly-vertical cliffs, which poses huge challenges for the transportation of materials and water, he said. Also, the thin and layered sandstone around the tunnel would possibly collapse and further increase safety risk, he added.
The tunnels, including the Hankou Tunnel, along the Jincheng-Xinxiang Expressway, total only 7 kilometers in straight-line distance, but they actually stretch 27 kilometers in the mountains, Ma told the People’s Daily. What he said demonstrated from the side the difficulty of the project.
To tackle the challenges, the project department employs the BIM+ (Building Information Modeling+) technology, a cutting-edge tool that is widely used in housing projects but rarely in tunnel construction.
“We are not taking the technology simply as an animation display, but a smart brain that guides the construction of the project and makes the construction safer, more efficient and more precise,” Ma said.
The BIM+ technology is able to generate geographical profile models based on investigation drawings, which helps constructors make pre-warnings of possible collapses and rock bursts in the Hankou tunnel that features complicated lithological changes.
“We categorized the wall rocks in accordance with their hardness and integrity,” Ma introduced, saying that different excavation methods are adopted for different wall rocks. According to him, the BIM+ is also connected with an air monitoring device to monitor real-time air quality and oxygen content, so as to ensure the health of the constructors.
In addition, the BIM+ is also making management more efficient. “We installed cameras at the tunnel entry, in the tunnel and on the construction vehicles, so that we can see in the office what is happening at the construction site,” Ma said, explaining that it is not easy to reach the construction site due to the poor road conditions. Thanks to the cameras, engineers can now guide workers to solve the problems at site from the project department, which saves plenty of time.
Besides, the BIM+ can automatically calculate in advance the consumption of steel bars and concrete of each section, and every batch of these materials is recorded with corresponding codes, so that they can be traced once problems are identified.
The tunnel will be installed with more sensors to capture ground settlement and crown settlement, and these data will be input into the BIM+ system for analysis for construction guidance and pre-warning, so that the construction will be smarter and safer, Ma said.
The expressway where Hankou Tunnel locates connects Henan province’s Xinxiang and Jincheng of north China’s Shanxi province. It will further complete the expressway network in northwestern Henan once it opens to traffic. The Hankou Tunnel is expected to be holed through at the end of 2022.