After three years of construction, on May 23, the left tube of the Lianfeng Tunnel—the longest tunnel on the Daguan to Yongshan Expressway in Zhaotong, Yunnan (abbreviated as the Dayong Expressway), a major corridor from Yunnan into Sichuan—was successfully holed through, laying the foundation for the full line to open to traffic within the year.

As the ** long tunnel on the entire line and a controlling project of the whole route, the Lianfeng Tunnel is being built simultaneously on the left and right tubes by China Railway Tunnel Group. Its right tube is 11 kilometers long, and the left tube holed through this time is only 5 meters shorter than the right tube, reaching 10.995 kilometers. The construction area is located in the Wumeng Mountains, where the terrain is highly undulating and groundwater is abundant. During construction, four relatively large water inrush emergencies occurred in succession. At the same time, complex geological conditions led to frequent geological hazards such as karst collapses, large deformations, and high ground temperatures.

In response, the construction unit organized and invited tunnel construction experts to conduct on-site surveys on multiple occasions, and after comprehensive analysis and assessment decided to adopt a curtain grouting scheme to effectively solve the on-site water hazards. In view of the ambient temperature in the construction area exceeding 37 degrees Celsius caused by high ground temperatures, various measures such as improving fan efficiency and shortening the shift times of workers were taken, so that construction and production advanced steadily while ensuring personal safety.

During construction, the participating personnel also adopted targeted measures such as reducing blasting intensity and strengthening tunnel support to solve construction difficulties such as broken fault-zone surrounding rock and operations at intersections of irregular sections. They used cross passages to add water storage tanks and uniformly set vehicle traffic routes, effectively solving the difficulties of long-distance transport and reverse-slope drainage.

According to reports, the right tube of the Lianfeng Tunnel is expected to be holed through in mid-June. Once the entire tunnel is holed through, it will lay the foundation for the full line to open to traffic on October 1 this year. After opening, it will end the history of Yongshan County having no expressway access, and Zhaotong City will also achieve "expressway access in every county."