Good news from China's most difficult tunnel!

"It takes only seven minutes for the train to cross the 14.5 km Dazhushan tunnel, but few people know that Jiang Dong and his brother have spent 13 years of their youth for the smooth passage of more than seven minutes..." Do you remember this "China's most difficult tunnel"? On June 26, 2019, good news came from it. In the morning, the parallel pilot tunnel of Dazhushan Tunnel of Darui Railway passed through smoothly, which laid a solid foundation for the comprehensive connection of the whole tunnel in 2020.

What is tunnel leveling?

The horizontal guide is a tunnel parallel to the main tunnel, and the construction should be ahead of the main tunnel. The main function is to provide geological reference for the excavation of the main tunnel. At the same time, through the cross passage between the horizontal guide and the main tunnel, the working surface of the main tunnel construction can be increased, the overall construction progress of the tunnel can be accelerated, and the functions of drainage, slag discharge, ventilation and transportation of construction materials can be achieved. After the completion of the tunnel, Pingdao can also play an important role in emergency evasion and line maintenance.

Dazhushan Tunnel, known as "the most difficult tunnel in the world" and "China Tunnel Construction Geology Museum", is located in Baoshan City, Yunnan Province. It is one of the controllable projects of Dali-Ruili Railway. It crosses the southern section of the famous Transected Mountains. The length of the tunnel is 14484 meters and the maximum depth of the tunnel is 995 meters. The geological environment of the tunnel is complex and the fault structure is well developed. It has the characteristics of "three highs" (high geothermal, high geostress, high seismic intensity), "four active" (active neotectonic movement, active geothermal water environment, active external dynamic geological conditions, active shallow surface reconstruction process of bank slope).

The longitudinal slope in the cave is designed as a small "man" slope with a maximum of 23.5. It passes through six fault zones, five karst development zones and three fold structures. The geology is extremely complex and changeable through the radioactive site supervision area and low-high temperature zone, and the construction is extremely difficult. During the most difficult period, the builders worked 24 hours in shifts and only excavated 156 meters in 26 months.

Since the construction of Dazhushan Tunnel in 2008, the water inflow has been about 200 million cubic meters, which is equivalent to the water inflow of 15 West Lake. Meanwhile, the high ground temperature section in the cave has long been in harsh construction environment of about 40 degrees Celsius and over 85% humidity. Due to the extremely harsh construction environment and the extremely difficult construction, the construction period of Dazhushan Tunnel was adjusted from the initial five and a half years to eight years, and then again to 13 years. At present, the main tunnel of Dazhushan Tunnel still has 1.8 kilometers left, which is expected to be fully connected by 2020.

After the tunnel was completed, it took only a few minutes for the train to pass through, but few people knew that more than 2,000 builders had spent more than 10 years here. Some of them had just graduated from college, and now their children were in primary school. Some of them came as young people and are now middle-aged with white temples. "When the tunnel runs through, my daughter should go to college, which is as good as I am from elementary school to college." Jiang Dong, manager of Darui Railway Project Department of China Railway Bureau 1, said.

Da-Rui Railway is one of the projects of improving the layout of railway network and developing new lines in the west of China in the medium and long-term railway network planning of China. It is also an important part of China-Myanmar international railway corridor, one of the entry and exit corridors in the southwest of China. It is also an important link of China's economic corridor connecting the Central-South Peninsula.

The Da-Rui Railway is also an important channel for implementing the national strategy of developing the western region, remolding the "ancient Southern Silk road" and highlighting Yunnan's role as a bridge and link facing Southeast Asia and South Asia. The construction of Da-Rui Railway will have a significant and far-reaching impact on promoting the economic and social development of the areas along the railway, promoting the implementation of the "precise poverty alleviation" work in Yunnan Province, enhancing the level of Yunnan's opening up, and promoting the exchanges and cooperation between China and Southeast Asian and South Asian countries.