The Dazhushan tunnel, the riskiest digging on the Dali-Ruili Railway in southwest Yunnan province, was drilled through at 8:36 on April 28. It took 12 years for the diggers to make the breakthrough, finally. They were excited at the feat, hugging each other to mark the occasion.

Dazhushan is the riskiest tunnel on the Dali-Ruili Railway, with its digging kicked off on August 8, 2008. The tunnel was first expected to be holed in 5 and a half years, which was adjusted to 8 years. It took 12 years in the end! 

It’s quite beyond us that it took 12 years to dig a 14.5-km tunnel. What a challenging project! In the past 12 years, many of the diggers in their 20s have become fathers.

The Dazhushan tunnel is actually the most challenging project on Chinese railways. It can even be taken as a miracle in tunnel engineering worldwide. Few can imagine how difficult it is in digging the tunnel. Here are some figures:

Water drained in great amount 

The tunnel runs through six faults in the southern section of the Hengduan Mountains, with the maximum depth reaching 995 meters. 

As a result, gushing water often occurred during the construction. The water amount mounted to 200 million cubic meters, which is 15 times as much as that in the West Lake in east China’s Hangzhou.

The water inflow in the tunnel can reach 12,000 cubic meters per hour, with a top 3-MPa pressure, equivalent to that in the sea 300 meters deep.

To drain out a daily maximum of 220,000 cubic meters of water, 7 pumping stations were built in succession, with 56 large pumps working concurrently. 116 pumps wore out.

20-ton ice daily for 40-degree temperature

Geothermal energy abounds in Baoshan, where the tunnel happens to pass through. "It seems that we’re digging a hole in the volcano," joked a worker.

In the tunnel under construction, the temperature can be over 40 degrees, with a humidity of 80%. To cool down, the workers need 20 tons of ice cubes every day.

Workers have to take breaks every 20 minutes in the hole, with each shift lasting three hours. At times, they can advance only 1 meter a day! 

26 months to dig 156 meters 

The Yanziwo/swallow nest fault makes the most difficult tunnel section. And it took them 26 months to dig the section of 156 meters.

The fault resulted in frequent gushing water in great amount. Once, a 13-ton excavator nearby was washed 40 meters away by the gushing torrent.

During its drilling, this tunnel presented engineers the biggest challenges: faults, mud, gushing water, weak rocks, geothermal heat, rock burst, gas, and radiation. 

"Here is a geo-museum. We’ve encountered all the possible risks in tunnel digging," said Jiang Dong, manager of No 4 Company of China Railway First Group Co, which is digging the tunnel.

The tunnel was build on wax-like earth fractures, which triggered frequent falls, collapses, and other fragile conditions. 

In 2013, a mud-gushing sealed a 200-meter-long and 6-meter-high tunnel section in 5 hours.

Why didn’t they choose an easier site for the tunnel? 

During the survey and design, more than 60 schemes were proposed for site selection, and the chosen one turned out to be the best, said experts. 

When the railway is put to use, it’ll only take a train 7 minutes to pass through the Dazhushan Tunnel. The passengers should remember the tunnel diggers who devoted 10 plus years to the project.

April 28, 2020 is a special date. 

The Dali-Ruili Railway starts from Dali City in Yunnan. Running westward through the localities of Baoshan, Shidian, Longling and Mangshi, it ends in Ruili, a town near the China-Myanmar border.

As part of the China-Myanmar Railway and the Pan-Asia Railway network, the 330-kilometer railway will open to traffic in 2022.

When the railway is put to use, the Dali-Ruili trip will be cut to three hours. Let’s wait and see.