Two workers were killed and two others injured after a section of wall collapsed inside the Doi Luang railway tunnel on the Den Chai-Chiang Rai-Chiang Khong railway project in Doi Luang district, Chiang Rai, on 20 June 2026. The collapse occurred in an area of the tunnel that had not yet been lined with concrete, with debris falling onto workers inside the construction site.
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According to project engineer Pattapong Boonkaew, the Doi Luang tunnel is 3.4 kilometres long and was successfully bored through last year. Construction is currently focused on installing a permanent concrete lining to protect the tunnel walls, with more than three-quarters of the work already completed. The collapse occurred in an exposed section that was awaiting protective treatment as part of the normal construction process.
Pattapong said preliminary findings suggest the collapse was caused by an “unforeseeable geological event”. He explained that Chiang Rai has experienced unusually heavy and prolonged rainfall over the past two to three years, resulting in excessive water accumulation within rock layers beneath Doi Luang mountain. This is believed to have affected temporary support structures in the exposed section, causing a localised failure and collapse.
The engineer stressed that the tunnel’s main structure, including sections already lined with permanent concrete, remains stable and safe. He said the incident would not affect the overall construction schedule or the future safety of railway operations. Geological specialists will now conduct a detailed assessment of rock conditions, while additional safety measures and reinforced temporary supports will be introduced to prevent similar incidents.
Authorities confirmed that two workers died at the scene and two others were injured. All casualties were transferred to Chiangrai Prachanukroh Hospital.
Chiang Rai Governor Chucheep Pongchai visited the site shortly after receiving reports of the incident. He said he had been attending official duties in Wiang Kaen district when informed by the Doi Luang district chief. The matter was immediately reported to the Director-General of the Department of Disaster Prevention and Mitigation and the Permanent Secretary of the Ministry of Interior, who were attending duties with the Prime Minister.
The governor said the Prime Minister had expressed concern and ordered an immediate on-site assessment. He described the collapse as an engineering accident influenced by natural factors, including persistent rainfall. He added that accumulated rainfall data would be incorporated into future construction planning during the wet season.
Authorities have coordinated with Chiangrai Prachanukroh Hospital to ensure support and compensation for the injured workers and the families of those who died. Chucheep emphasised that the collapse was confined to a specific construction area within the tunnel and did not involve a major structural failure of the project.
Matichon reported that the Den Chai-Chiang Rai railway project was approved by the Cabinet on 31 July 2018 with a budget of 85.345 billion baht and a construction period of seven years. The line is expected to open in January 2028 and includes four railway tunnels.
Pictures courtesy of Matichon
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Adapted by ASEAN Now Matichon 21 June 2026
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