The Sangmaying No. 2 Tunnel on Section 4 of the Guinan High-Speed Railway was successfully holed through recently. This is the first long tunnel over 2,500 meters to be completed in the Guizhou section of the Guinan High-Speed Railway.

The Sangmaying No. 2 Tunnel is located on the section between Duyun East Station and Dushan East Station of the Guinan High-Speed Railway, with a total length of 2,585 meters. The tunnel site area features the erosional and karst landforms of the Yunnan-Guizhou Plateau. The entire tunnel has a single-face upgrade gradient of 12.2‰, with a maximum burial depth (the distance from the mountaintop to the tunnel crown) of 150 meters. The tunnel's geological conditions are complex, and during excavation, collapse and rockfall are highly likely to occur, affecting the construction schedule.

Construction at the tunnel entrance began on October 10, 2018. Due to the influence of geological conditions, progress was slow, and single-head excavation posed a risk of affecting the girder erection schedule. The project department decided after study to add a working face at the tunnel exit, where construction began on July 26, 2019.

To ensure the smooth progress of tunnel construction, the Party Working Committee of the Section 4 Project Department carried out overall planning, held multiple special meetings, and conducted process simulations to ensure that construction personnel, equipment and materials, technical follow-up, and safety management were in place; it organized construction and implemented plan assessments to ensure that milestones remained controllable. The project department overcame unfavorable geological conditions such as thick soil layers, dangerous rockfalls, and karst, promptly discharged seepage water out of the tunnel during construction, and adopted controlled blasting measures to ensure the safety of houses and roads. The tunnel was holed through as scheduled on March 11 this year.

The Guinan High-Speed Railway is a component section of the Baotou-Haikou corridor of the “eight vertical and eight horizontal” high-speed railway network in China's Medium- and Long-Term Railway Network Plan. It is the first double-track high-speed railway with a design speed of 350 kilometers per hour in Guizhou and the southwestern region. The newly built line has a total length of 482 kilometers, of which the Guizhou section is 199.255 kilometers long. The entire line is expected to be completed and opened to traffic by the end of 2023. By then, the travel time by EMU train from Guiyang to Nanning will be reduced from the current more than 5 hours to less than 2 hours.