In less than a month, the tunnel in Yunnan has reduced its diameter from 12 meters to less than 3 meters due to tectonic plate shifts.
A bridge leading into the Kaba Snow Mountain Tunnel, one of 20 tunnels on the Yunnan-Tibet railway. (Photo: SCMP)
The forces of nature have posed an unprecedented challenge for engineers constructing a new railway line in southwestern China. Specifically, several completed sections of the 9-kilometer Kaba Snow Mountain Tunnel in Diqing Tibetan Autonomous Prefecture, Yunnan, are being compressed due to the collision of the Eurasian and Indian tectonic plates.
In less than a month, this tunnel has shrunk from a diameter of 12 meters to less than 3 meters, barely enough for a vehicle to pass through, the project engineering team reported to Science and Technology Daily on July 27.
Measurements taken with specialized equipment indicate that the rock surrounding the tunnel is under pressure of up to 30 megapascals, equivalent to the total weight of 75 elephants standing on one foot. The rocks, primarily formed from lava, are not sturdy enough to withstand this pressure.
“The Kaba Snow Mountain Tunnel completely surpasses my understanding of tunnel construction. Currently, it is the most challenging tunnel in China, with rates of deformation, construction time, and damage all breaking previous records,” said Tian Weiquan, project manager at China Railway Group 6.
The project team is attempting to support the tunnel with super-strong reinforced concrete structures designed to meet high safety standards. However, the immense pressure is turning cement into dust and destroying even the strongest steel bars.
The Kaba Snow Mountain Tunnel’s diameter has reduced from 12 meters to less than 3 meters in about 20 days due to the collision of the Indian and Eurasian tectonic plates. (Photo: SCMP)
When completed, the Kaba Tunnel will be part of a 139-kilometer tourist route connecting Lijiang to Shangri-La. The route passes through many famous ancient towns and habitats of ethnic minorities, snow-capped mountains, and deep gorges in the southeastern Tibetan Plateau, operating at speeds of no more than 120 km/h. This railway will also connect Tibet with Southeast Asia, promoting economic development.
Construction began 8 years ago and is expected to be operational by the end of this year. The railway will pass through 20 tunnels, with Kaba being the last and the only one not yet completed.
Tian and his colleagues have found a solution to complete the project on time, which involves digging a smaller tunnel through the mountain to help relieve much of the pressure accumulated in the rocks. Once conditions stabilize, they will expand the tunnel size to meet design requirements. Currently, more than 1,200 workers are on site day and night, four times the previously planned workforce.
