The construction of the Gaoligong Mountain Tunnel on the Dali-Ruili Railway in southwest China's Yunnan Province is a testament to the builders' unwavering dedication. Despite complex geological conditions and numerous challenges, these workers have remained steadfast in their efforts to complete this monumental engineering feat.
The Dali-Ruili Railway, a vital link between Dali and Ruili cities in Yunnan Province, stands as a significant infrastructure project under the Belt and Road Initiative.
This railway, divided into two sections -- Dali to Baoshan and Baoshan to Ruili -- has already seen the completion of the Dali-Baoshan section in 2022 after 14 years of construction.
However, the full operation of the railway hinges on the completion of the Gaoligong Mountain Tunnel, a project fraught with challenges and known as the "world's most difficult railway tunnel to build" due to its complex geology, dense vegetation, and abundant underground water. With the tunnel in place in the future, the estimated travel time through the mountain will be reduced from about one day to just 15 minutes.
The entire railway spans 330 kilometers, with the Gaoligong Mountain Tunnel accounting for 34.538 kilometers, or one-tenth of the total length.
Construction of the Gaoligong Mountain Tunnel began in 2015, and this year marks its 11th year of work. Currently, 55.7 percent of the project is finished.
During the just-ended Spring Festival, a holiday of family reunion in China, many builders remained at their posts in the mountain.
The tunnel is being constructed simultaneously at five locations: the entrance and exit, two vertical shafts and one inclined shaft. The tunnel was so deep that workers must take a five-minute trip in a special elevator to reach the construction sites at the bottom of the shafts -- a route that took over four years to create.
The construction environment is extremely humid and sweltering, with temperatures reaching as high as 42 degrees Celsius. While the surface experiences distinct four seasons, the underground remains constant. Even the water is warm.
To address the issue of high underground temperatures, the tunnel is equipped with ventilation pipes to bring fresh air from the surface to each work site. A giant air conditioner is also installed to keep the temperature at around 34 degrees Celsius.
The tunnel is excavated using the blasting method. After each blast, workers have to advance with their hands inch by inch, aside from the debris removed by excavators.
Every 60 centimeters along the tunnel's arch, a support is installed. Due to the loose geological conditions, each blast affects the progress, limiting the speed. A successful blast that advances two meters is already considered a good result.
During construction, water ingress has been a frequent and significant challenge.
"During the well construction, the most feared situation is water gushing emergencies. The most severe high-pressure water gushing emergency we encountered had a water flow rate of 314 cubic meters per hour, which far exceeded our pumping capacity. In just one night, the 630-meter high shaft was completely filled with water, rendering all previous efforts in vain. It took us five months just to pump out the water," said Li Hang, project head of the first vertical shaft.
In 2018, China's self-developed Caiyun hard rock tunnel boring machine started to be used in the tunnel's construction. However, even with this powerful tool, excavation remained extremely difficult under the complex geological conditions of the Gaoligong Mountain.
The hard rock tunnel boring machine almost fills the entire tunnel, leaving construction workers with only a narrow space to complete all other procedures. Due to the high underground temperature, workers sweat a lot and consume a lot of energy. Their working time underground is generally controlled to two to three hours before rotation. Sometimes, a worker has to go up and down four or five times a day.
"We are now using manual methods to assist machine work. We first install a layer of arch supports and then proceed with shotcrete work. Each process basically takes two to three hours, and then another team has to take over. Otherwise, it's really unbearable for people to work in such a high-temperature environment for so long," said Cao Yaozu, chief engineer of the exit area of the project.
Reflecting the shared spirit of perseverance among the workforce, one worker expressed his commitment.
"This year marks my 11th year working on the Gaoligong Mountain Tunnel project. I will stay here out of dedication and passion until the tunnel is completed," said a worker.
Builders' dedication drives progress on "world's most difficult" railway tunnel
