Final Tunnel Breakthrough Completes Full Tunnel Works on Chongqing–Kunming High‑Speed Railway

According to People’s Network reports, the Zhaotong Tunnel achieved full breakthrough on the morning of 26 June, marking the completion of all tunnel construction sections along the entire Chongqing–Kunming high‑speed railway line. The milestone breakthrough represents major progress in China’s capability to build 350km/h high‑speed rail tunnels under extremely complex geological conditions, laying a solid foundation for the full opening of the key southwest transport corridor.

Located in Yiliang County, Zhaotong city within the remote Wumeng Mountain range, Zhaotong Tunnel is classified as a Grade I high‑risk engineering project. It spans 16.26 kilometres with a maximum burial depth of 980 metres and features a 1.6‑kilometre gradient section with a vertical climb of 478 metres, constructed as a single‑tube double‑track structure. As one of the earliest and most challenging control works on the route, the tunnel traverses 18 complex geological strata and two regional fault zones, combining multiple extreme construction hazards rarely seen in high‑speed rail projects worldwide.

The construction site faced overlapping geological difficulties including coal and gas outburst risks, severe large‑scale deformation of deep soft rock, active fault structures, intensive karst development and high‑pressure underground water systems. The maximum gas pressure recorded on site reached 1.83MPa, while maximum in‑situ stress hit 44.42MPa. Nearly 10 kilometres of the tunnel alignment was threatened by frequent mud and water inrush, with single working faces recording maximum daily water inflow of 130,000 cubic metres throughout the construction phase.

Full sets of specialised construction equipment, including explosion‑proof machinery, intelligent excavation devices, high‑pressure grouting systems, secondary lining facilities and real‑time stress monitoring instruments, were deployed to support site operations. Construction teams dynamically adjusted implementation plans according to evolving geological conditions and adopted rigorous rapid excavation, rapid support and rapid closure procedures. Systematic technological innovation effectively neutralised major safety risks and resolved complex on‑site technical bottlenecks, ensuring stable construction quality and continuous progress.

Yunnan Investment Railway, under Yunnan Investment Group, has delivered robust financial backing for the mountainous rail project. As the sole provincial fund representative for Yunnan’s railway development, the entity has injected a total of 25.8 billion yuan into the project, setting a new record for provincial railway investment in Yunnan and delivering stable financial support for the challenging cross‑mountain infrastructure scheme.

The full breakthrough of Zhaotong Tunnel concludes all subgrade, tunnel and bridge works across the Chongqing–Kunming high‑speed railway. Subsequent station and auxiliary engineering works are advancing steadily, with track laying on the Kunming–Zhaotong section nearing completion. External environmental renovation and municipal supporting facilities are being implemented in parallel, maintaining efficient overall project progression.

The 700‑kilometre Chongqing–Kunming high‑speed railway forms a vital component of China’s national eight vertical and eight horizontal high‑speed rail network and represents Yunnan’s first 350km/h high‑speed railway route. Upon full operation, the line will shorten travel time between Kunming and Chongqing to approximately two and a half hours, and cut journeys between Kunming and Chengdu to under three hours.

The upgraded transport corridor will strengthen fast connectivity between the Chengdu‑Chongqing twin‑city economic circle and the central Yunnan urban agglomeration, enabling efficient flows of passengers and cargo across southwest China. The high‑speed rail network expansion will continuously boost high‑quality socioeconomic development throughout the regions along the route.