The photo shows the right-line portal of the Zhongtianshan Tunnel, completed ahead of schedule by China Railway Tunnel Group.

      The Zhongtianshan Tunnel is located in the ridge area of the eastern section of the Middle Tianshan Mountains in Toksun County and Hoxud County of southern Xinjiang, with a maximum altitude of 2,951.6 meters, a maximum burial depth of 1,728 meters, and a designed longitudinal slope of 11 per mille. The tunnel passes through the Middle Tianshan Mountains, connecting Toksun County to the north and Hoxud County to the south. It is a double-tube, single-track tunnel with a total length of 22.449 km. The tunnel straightens the original route of the Southern Xinjiang Railway that crossed the Middle Tianshan Mountains, shortening the journey by 123.6 km. Construction began in April 2007; the right tube broke through in September 2013, and the entire line broke through in February 2014. It is expected to be put into operation by the end of 2014.

      The Zhongtianshan Tunnel, with a total length of 22.449 km, is a key controlling project of the second line of the Southern Xinjiang Railway from Turpan to Korla that breaks through the Tianshan barrier. The second line of the Turpan-Korla Railway has a total length of 334.12 km. It is the main railway corridor from southern Xinjiang to northern Xinjiang and the interior of China, and also an important part of the new Silk Road connecting China with the Eurasian continent.
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      Geological environment
      The Zhongtianshan Tunnel is located in the barren Gobi mountains, where the natural environment is harsh. It is characterized by “four highs and one rich”: high ground stress, high temperature, high humidity, and high-pressure water-rich conditions. The geological environment is complex and changeable, and the pressure of sudden water inrush is rare in China. Rockbursts and rock thrusts occur from time to time, and the working faces inside the tunnel are extremely humid with highly corrosive water quality. The tunnel construction is located in a warm temperate arid climate zone, where it is dry and receives little rain, winters are cold and windy, and the temperature difference between day and night is large. In summer, daytime temperatures reach above 43 degrees Celsius, while in winter the temperature outside the tunnel drops below minus 28 degrees Celsius. The construction environment is extremely difficult. In particular, reverse-slope drainage in the long tunnel is difficult, and various construction challenges converge, making the construction difficulty very rare in China.
      Key and difficult points of the project
      Project focus: The Zhongtianshan Tunnel is a controlling project for the entire line. The AK2 section constructed by China Railway Tunnel Group has only three working faces: the entrance, the exit, and the inclined shaft (which itself must be excavated 2,545 m to reach the main tunnel). Among them, the TBM needs to pass through a 2,895 m granite section. How to improve the TBM's excavation efficiency, especially in the granite section, is the focus.
      Technical difficulties

      1. Complex geology: The tunnel body passes through 3 major regional fault zones (F2, F3, F4) and 8 secondary fault zones, with well-developed structural fissure water. Adverse geological conditions mainly include high ground stress, sudden water inrush, high ground temperature, and rockbursts.
      2. Inclined shaft construction: The No. 2 inclined shaft is 2,545 m long, with a tunnel cross-section of 32 M2 and an average slope of 11%. Reverse-slope drainage and transportation problems in the long and large tunnel are prominent.
      3. Ventilation for long-distance blind heading: First, excavation at the exit working face; second, excavation at the inclined shaft working face. In the early stage, blind ventilation was used for the 4.5 km exit section and the 5.3 km inclined shaft working section to solve the ventilation problem inside the tunnel. In the later stage, blind ventilation must be solved for the 8.68 km drill-and-blast section.
      4. High organizational requirements for simultaneous TBM excavation and secondary lining construction.