After eight years of effort, a group of Chinese workers has completed the construction of a railway linking Lanzhou and Chongqing, finally conquering the Humaling Tunnel, which is considered one of the hardest railway projects in the world.

The tunnel connects Xiaguanying in Lanzhou to Min County in Dingxi, where complicated geological conditions have long obstructed the construction of the railway. Water-rich sand stratum is the hardest problem to solve, as it causes the surrounding sand to break apart and flow. Construction workers compare the drilling of the tunnel to digging through soft tofu.

“Building a tunnel in water-rich sand stratum has no precedent, but the workers independently created a sound construction plan in 2015,” said Chen Dongjie, vice general-manager of the Lanzhou-Chongqing Railway Company.

Lanzhou-Chongqing railway, on which construction began in September 2008, stretches 873 kilometers and was built using a total investment of 82.92 billion RMB. Connecting with Chongqing-Guiyang railway, it represents one of the three railway arteries to link Lanzhou, Chongqing and Guangzhou.

The running time from Lanzhou to Chongqing will be shortened to six hours after completion of the railway, which is expected to fully open to traffic at the end of 2017.