The Department of Rail Transport (DRT) has attributed the recent collapse of the Khlong Phai tunnel on Thailand’s high-speed rail line to geological instability. The incident, which occurred on August 24, 2024, at around 11 p.m., tragically claimed the lives of three foreign workers and damaged machinery involved in the construction. According to officials, the collapse resulted from weak rock formations and unstable geological conditions in the area.
The Khlong Phai tunnel is part of the high-speed rail project connecting Bangkok to Nakhon Ratchasima. The section where the collapse occurred is on a steep slope and situated within a curved segment of the tunnel, spanning from kilometer marker 189+390 to 189+460. This area is characterized by weak and fractured rock formations, particularly a type classified as “Very Poor Rock” (Vb), which is prone to significant erosion and instability. The surrounding geology includes siltstone and shale mixed with weak sandstone, all located below the waterline of the nearby Lam Takhong Reservoir.
The collapse occurred as workers were removing soil and rock from the tunnel, with large rocks breaking away from the roof and walls. An official investigation found that geological factors—such as weak rock formations, uneven erosion, and high water pressure in the tunnel’s surrounding areas—likely caused the incident. Reports suggest that the structural integrity of the tunnel could not withstand the pressure, leading to a failure of the initial support system installed during construction.
In response to the incident, the Department of Rail Transport has outlined five key measures to prevent similar events in the future. These include enhanced real-time monitoring of tunnel movement, the installation of automatic extensometers to measure ground shifts, and strict adherence to construction methods and risk mitigation procedures. Additionally, areas with significant geological changes will be re-evaluated to ensure that construction methods are adjusted accordingly.
The high-speed rail project, which is 77.09% complete, remains halted following the incident. The Ministry of Transport has instructed the State Railway of Thailand (SRT) to cease construction until a full investigation is conducted. The SRT will also consider whether contract extensions are necessary due to the delay caused by the collapse.
Key figures attending the investigation include Pichet Kunadhamraks, Director-General of the Department of Rail Transport, alongside representatives from the National Science and Technology Development Agency, the Thailand Council of Engineers, and the State Railway of Thailand, among others.
