A wall inside the "Doi Luang Tunnel" collapsed on workers during construction of the Den Chai-Chiang Rai railway line, killing 2 and injuring 2. The project engineer suspects the cause is related to unstable weather and accumulated rainwater. The Chiang Rai governor emphasized it was an unavoidable accident that does not impact the main structure.
At approximately 16:00 on 20 Jun 2026, a collapse occurred inside the Doi Luang Tunnel on the Den Chai-Chiang Rai-Chiang Khong railway line in Doi Luang District, Chiang Rai Province, resulting in 2 immediate fatalities and 2 injuries.
Mr. Patthapong Boonkaew, the project engineer, explained that the Doi Luang Tunnel is 3.4 kilometers long. Drilling through was completed last year, and permanent concrete lining is underway to protect the tunnel walls, with over three-quarters of the work finished. The collapse occurred at a section of the wall still exposed and awaiting protective lining.
The preliminary cause is believed to be a "geological force majeure," as Chiang Rai has experienced abnormal weather and heavy rainfall over the past 2-3 years. Excessive water accumulated in the rock layers of Doi Luang Mountain, exceeding initial estimates, leading to temporary support structures failing and a localized wall collapse at the exposed tunnel section.
However, Mr. Patthapong firmly confirmed that the main structure where concrete lining is complete remains stable and safe. This incident will not affect the overall construction schedule or future operational safety. Geological experts will conduct detailed rock layer assessments, and safety and temporary support measures will be strengthened to prevent recurrence. The casualties include 2 deceased and 2 injured, all immediately transferred to Chiang Rai Prachanukroh Hospital.
Mr. Chucheep Pongchai, Governor of Chiang Rai, who promptly visited the site after the report, stated he was on duty in Wiang Kaen District when informed by the Doi Luang District chief. He quickly reported to the Director-General of the Department of Disaster Prevention and Mitigation and the Permanent Secretary of the Ministry of Interior, who were on duty with the Prime Minister. The Prime Minister expressed serious concern and instructed the governor to inspect the situation immediately and report back.
The Chiang Rai governor added that this was an engineering accident beyond control, influenced by natural disasters and heavy rainfall. Relevant agencies and contractors must analyze accumulated rainfall in planning construction during the rainy season. He has coordinated directly with Chiang Rai Prachanukroh Hospital's director to ensure comprehensive care and support for the injured and families of the deceased. He reassured the public that this was a localized collapse within the construction site, not a catastrophic structural failure, and the project will continue as planned.
The Den Chai-Chiang Rai railway line was approved by the Cabinet on 31 Jul 2018, with a budget of 85.345 billion baht and a 7-year construction period, aiming for completion and service launch in Jan 2028. The project includes four tunnels, the longest being the Ngao Tunnel in Lampang Province at 6.24 kilometers. Others include tunnels in Phrae, Phayao, and Doi Luang. Construction progress stands at 64.448%, slightly behind the planned 65.092% by 0.644%, with visible trackwork outside the tunnels along the route.