Paomashan No. 1 Tunnel

On January 18, the Kangding Bypass Section of the Ya'an (Sichuan) to Yecheng (Xinjiang) National Expressway (hereinafter referred to as the "Ya-Ye Expressway") achieved a major milestone — the Paomashan No. 1 Tunnel was fully holed through on both tubes, laying a solid foundation for the opening of the entire Kangding Bypass Section of the Ya-Ye Expressway.

Invested by Zanggao Yakang Company of Shudao Group and constructed by Sichuan Road & Bridge Transportation Construction Group, the Paomashan No. 1 Tunnel is located in Kangding City, Ganzi Prefecture, Sichuan Province. Its left tube is 8,865 meters long and its right tube 8,780 meters long, making it a two-tube, two-way separated extra-long "S"-shaped curved tunnel. The tunnel portal sits at an elevation of 2,388 meters and the exit at 2,608 meters, an elevation difference of 220 meters — equivalent to the height of an 80-story building — the largest elevation difference between the inlet and outlet of a single expressway tunnel in the world.

The Paomashan No. 1 Tunnel lies in the transition zone between the Sichuan Basin and the Western Sichuan Plateau, a typical area of high altitude, severe cold, and high seismic intensity. It crosses the Longmenshan and Xianshuihe fault zones, with seismic intensity reaching Grade IX, extremely complex geological conditions, and extremely high construction difficulty. In addition, the tunnel's maximum burial depth reaches 1,250 meters, resulting in high in-situ stress in the rock mass and great variation in lithology; 51% of the tunnel is in rockburst zones, and since construction began in January 2018, a total of 425 rockbursts of varying sizes have occurred. Water inflow in some construction areas is severe, with a maximum daily inflow of 12,500 cubic meters — equivalent to the volume of 28 standard indoor swimming pools.

Faced with a series of challenges, the participating units took multiple measures and adopted a number of special measures to tackle the difficulties. On the one hand, they used three-boom rock drilling jumbos, added advanced pressure-relief holes, applied water spraying, and set up rockburst emergency escape passages to overcome the interference of high in-situ stress and ultra-high-frequency rockbursts on construction and to ensure the safety of frontline workers. On the other hand, they adopted an "S"-shaped curve design, which underwent three turns totaling 341 degrees, to reduce the gradient, solve the problem of the elevation difference between the inlet and outlet, and further enhance traffic safety.

At present, tunnel excavation for the Kangding Bypass Section of the Ya-Ye Expressway is 96% complete, the bridge substructure is 100% complete, the superstructure is 100% complete, and the roadbed works are 80% complete.

The Kangding Bypass Section of the Ya-Ye Expressway is part of the Chengdu–Kangding–Tibet Expressway in the Sichuan Provincial Expressway Network Plan (2014–2030). Once completed, driving from Kangding urban area to Xinduqiao will be shortened by more than one hour, which will effectively divert through traffic from Kangding's urban area, ease congestion pressure in the main urban area, and promote all-for-one tourism development. It is of positive significance for strengthening links between the Chengdu Plain and Tibetan-inhabited areas and enhancing emergency support capacity.