Twelve project managers and safety officials are facing administrative penalties following the release of an investigation into a catastrophic water and mud inrush at a high-speed railway tunnel site in July 2025 that left seven workers dead and four others injured. The results of the investigation were published by the Zhaotong Emergency Management Bureau on Monday.

On July 12 last year, a water and mud inrush accident occurred at the working face of the Zhaotong Tunnel on the Chongqing—Kunming High-Speed Railway Yunnan—Guizhou section, which was under construction in Zhaotong city.

According to the released report, fractured surrounding rock, rockfalls and seepage water were observed at the tunnel's working face on the morning of July 10. The construction unit halted operations and set up warning signs while, on July 11, a joint site meeting decided to suspend construction.

However, on the morning of July 12 personnel entered the tunnel for work and, shortly after 12 pm, a sudden water and mud inrush occurred at the working face, discharging approximately 6,000 cubic meters of mud and about 100,000 cubic meters of water, sweeping 11 workers to locations ranging from 200 to 700 meters away from the working face. While seven workers died, four recovered from their injuries following hospital treatment.

According to the report, the initial inrush was compounded by the project participants' weak risk awareness, inadequate effectiveness in hazard identification and control, insufficient precautions and improper handling of abnormal operating conditions.

Additional contributing factors included heavy rainfall, soluble rock formations, tectonic fracture zones and high-level water-rich bodies.