After 609 days, on the morning of January 20, the right tube of Chunping No. 2 Tunnel in Section A4 of the Dayong Expressway was successfully holed through, marking the first tunnel breakthrough on the Dayong Expressway.

　　Chunping No. 2 Tunnel, constructed by China Railway Construction Bridge Engineering Bureau Group, has its entrance located in Jinzhulin, Luxi Village, Huanghua Town, Yongshan County, and its exit located in Yujiahegou, Luxi Village. It is designed as a separated double-tube tunnel. The left tube has a total length of 1,161 m and a maximum burial depth of about 345.0 m, while the right tube has a total length of 1,196 m and a maximum burial depth of about 372.0 m.

　　According to Zhang Xuehui, chief engineer of Section A4 of the Dayong Expressway under China Railway Construction Bridge Engineering Bureau Group, when excavation of Chunping No. 2 Tunnel first began, the portal was situated atop a cliff, with 47,500 cubic meters of dangerous rock above the tunnel crown reaching as high as 82 m, crisscrossed by cracks on a steep, high mountain, making mechanical equipment unusable for construction. For this reason, the project department could only use manual blasting and manual clearing to eliminate the hazards. It ultimately took more than seven months to deal with the dangerous rock and remove the safety hazards. In addition, during tunnel construction, unfavorable geological conditions such as karst caves, landslide bodies, gravelly soil, and large water inflows were encountered many times.

　　In response to these problems, the A4 project department actively cooperated with the Dayong Expressway Construction Headquarters, strengthened construction organization, carefully studied countermeasures, added pipe roofs and increased advance support, strengthened support measures, and repeatedly invited experts to study and verify the plans on site. On the basis of the original design, measures such as increasing the number and strength of advance supports were adopted to ensure construction safety and steady progress of the project.

　　The main line of the Dayong Expressway is 61.691 km long, with an estimated total investment of 12.7347 billion yuan. The project starts north of the Shanggaoqiao interchange of the G85 Yinkun Expressway near Shanggaoqiao Village in Daguan County and ends at the Yunnan-Sichuan provincial border, connecting to the tail end of the Yunnan abutment of the bridge over the Jinsha River on the Yongshan branch of the national expressway network G4216. It is another important interprovincial corridor from Yunnan into Sichuan. The entire line passes through deep mountains and gorges, with a bridge-to-tunnel ratio as high as 94.4%, making it one of the expressways under construction in the city with greater construction difficulty. The successful breakthrough of the right tube of Chunping No. 2 Tunnel not only set an example for all projects along the line but also strengthened everyone's confidence in overcoming difficulties.