At 10:36 on January 20, after 13 years of arduous efforts, the parallel adit of Xiuling Tunnel, constructed by the Group Company, was successfully holed through. The parallel adit has been excavated to 9,677 meters from a single heading! As the longest single-head excavation tunnel on the entire line, it has once again broken the Asian record for the longest single-head excavation of a railway mountain tunnel. Officials from the Dali Prefecture Transportation Bureau, Yangbi County, Yungui Company and other government and relevant units attended the breakthrough ceremony. Xia Fabao, Assistant General Manager of the Group Company, attended the ceremony and delivered a speech.

The builders of the Group Company have been stationed at Xiuling Tunnel for 13 years. Once the Dali-Ruili Railway is fully open, trains will pass through Xiuling Tunnel in only about 8 minutes. Since construction began in 2008, the Group Company has continuously strengthened construction organization research, deeply optimized construction plans, constantly innovated techniques and methods, strived to solve construction difficulties, and focused on researching and solving various prominent problems restricting rapid project progress. In the construction of Xiuling Tunnel, by taking the lead in introducing the cantilever roadheader construction technology in railway single-track tunnels, deeply promoting standardized techniques and methods, continuously improving the high-ground-temperature working environment of extra-long tunnels, and striving to enhance the ability to cope with complex and special geological conditions, the safe and smooth breakthrough of the parallel adit was achieved.

Xiuling Tunnel is located in Yangbi County, Dali Prefecture, Yunnan Province, with a total length of 17.623 kilometers and a maximum burial depth of 1,115 meters. It crosses the Hengduan Mountains and passes through 7 fault zones. Most of the tunnel body lies in the soft rock of the "Western Yunnan Red Beds," with frequent geological hazards such as faults, fracture zones, interlayer compression zones, high ground stress, and mud and water inrushes. The surrounding rock changes frequently, groundwater is abundant, and construction is extremely difficult. The breakthrough of the parallel adit has created multiple milestones in China's tunnel construction!

Set a new record for the longest single-head excavation tunnel in Asia

As a key control project of the Dali-Ruili Railway, Xiuling Tunnel is one of the longest and most difficult tunnels on the entire route. At present, in the construction of extra-long tunnels in China, most adopt methods such as setting up cross adits, inclined shafts, and vertical shafts to increase excavation faces and achieve "long tunnel, short driving" to improve construction speed. However, limited by geographical and topographical conditions, Xiuling Tunnel can only adopt long-distance excavation from both the entrance and exit, which makes it difficult to speed up tunnel construction and results in slow progress, becoming a "super obstacle" affecting the full opening of the Dali-Ruili Railway.

As the tunnel goes deeper, another headache for the builders follows—high ground heat. Since January 2017, the working face at the entrance of Xiuling Tunnel has shown temperatures above 35°C, and the air humidity inside the tunnel is close to 100%. The temperature at the working face can reach up to 40°C, greatly reducing construction efficiency.

To improve the working environment and enhance operational efficiency, both the entrance and exit work sites transport more than 10 tons of ice to the construction site every day for cooling. At the same time, by improving the tunnel's ventilation method and air circulation mode, they ensure a temperature drop of more than 3°C and a dust reduction rate of over 95%.

Filled the gap in construction under "Western Yunnan Red Beds" geological conditions

Xiuling Tunnel is located in the Hengduan Mountains' western Yunnan high mountain and gorge area, with large terrain fluctuations. The locally unique Western Yunnan Red Beds are the only soil layer named after a region, composed of alternating mudstone, siltstone, and sandstone, brown in color, easily broken and deformed, severely weathered, and frequently changing. Often, the previous cycle is relatively stable hard rock, and the next cycle suddenly presents interbedded sandstone and mudstone; a slight negligence may even cause tunnel collapse. At present, there is little research on construction technology under the geological conditions of the Western Yunnan Red Beds in China, and no mature experience can be borrowed. When the construction personnel first entered the site, it could be said they were "crossing the river by feeling the stones."

"During construction, workers not only have to adapt to the harsh environment caused by the stuffiness from high temperatures and turbid air, but also face many difficulties such as large-scale collapses, large deformation of soft rock, and water and mud inrushes," said Wu Lijun, head of the entrance work site of Xiuling Tunnel. According to different rock properties and different construction conditions, they researched and formulated four levels of technical plans. Whenever problems are encountered during excavation in each shift, technical personnel will promptly adjust the construction plan and parameters.

To overcome world-class tunnel construction challenges such as mud and water inrushes, large deformation of soft rock, fault fracture zones, and high-temperature heat damage in Xiuling Tunnel, the Group Company carried out more than 100 research projects, obtained 2 national patents, 3 provincial and ministerial-level scientific research achievements, and 41 enterprise-level scientific research achievements, providing corresponding scientific research results and pioneering experience for future domestic "extra-long" difficult and key tunnels, especially the construction of the Sichuan-Tibet Railway. Among them, the innovative application of the cantilever roadheader method alone, compared with the drill-and-blast method, increased the average annual progress by more than 40% and saved more than 8 months of construction time.

Created the first track transportation in single-track railway tunnel construction

Because there are no conditions to open cross adits or inclined shafts, the frontal single-head excavation of Xiuling Tunnel will be 10 kilometers. If diesel vehicles are used for transportation inside the tunnel, the exhaust gas from vehicles deep in the tunnel is difficult to discharge, which will raise the temperature inside the tunnel and is also harmful to the health of workers ahead.

To ensure the construction environment inside the tunnel, the entrance construction section of Xiuling Tunnel adopts battery-powered tram transportation for construction organization. The transport trams adopt a large circulation mode of "entering via the parallel adit and exiting via the main tunnel." All vehicles entering the tunnel use the passing bays and cross passages of the parallel adit for meeting and passing. Although track transportation improves the environment inside the tunnel, it is not as flexible and convenient as automobile transportation, making it difficult to speed up tunnel construction.

"To this end, we set up a 'small railway bureau' inside the tunnel," introduced the construction manager. "On average, every 6 to 7 minutes there is a train entering the tunnel for transportation organization, dispatch, daily line inspection, maintenance, and upkeep, maximizing transportation efficiency and reducing the failure rate."

It is reported that the Dali-Ruili Railway has a total length of 330 kilometers and is an important project in China's "Medium- and Long-Term Railway Network Plan" for improving the road network layout and developing the western region. It is a major land transport corridor for connectivity between China and Myanmar and other Indochina Peninsula countries and access to the Indian Ocean. After completion and opening to traffic, it will connect the "last section" of the China-Myanmar International Railway within China, improve the transportation pattern of western Yunnan, and become an important trunk line of the China-Myanmar railway corridor. It will end the history of no train service in ethnic minority areas such as Baoshan City and Dehong Prefecture in Yunnan Province. At that time, the railway travel time from Dali to Ruili will also be shortened from the current 6 to 7 hours by road to more than 2 hours.