MRTA takes responsibility for road subsidence, to investigate all tunnels on Bangkok’s Purple Line
MRTA halts construction at Vajira Hospital site after road subsidence.
Investigation underway into Purple Line tunnel work; public safety measures in place.
The Mass Rapid Transit Authority of Thailand (MRTA) has taken responsibility for the road subsidence that occurred on September 24 in front of Vajira Hospital, Samsen Road, Dusit, Bangkok, near the construction site of Vajira Hospital Station (PP19) on the Purple Line of the metro.
The area of subsidence falls under Contract 1, which involves the design and construction of the tunnel and underground stations along the Taopoon-National Library section, covering a distance of 4.8 km and worth 19.43 billion baht. The contractor for this section is the CKST-PL Joint Venture, consisting of CH. Karnchang Public Company Limited and Sino-Thai Engineering & Construction Public Company Limited.
Construction halted for investigation
MRTA Governor Gardphajon Udomdhammabhakdi visited the site with officials from the Ministry of Transport to closely oversee the resolution. The MRTA has immediately halted construction at the affected area to investigate the cause.
The MRTA has also coordinated with utilities, including Metropolitan Waterworks Authority (MWA), Metropolitan Electricity Authority (MEA), telecommunications companies, and local police to address the situation swiftly. Traffic management in the area is also in place to facilitate public movement.
MRTA accepts responsibility for damages
Gardphajon explained that the cause of the subsidence is believed to stem from soil and groundwater movement beneath the 20-metre deep tunnel, leading to displacement between the tunnel and the station wall, which triggered surface soil subsidence. This also caused a main water pipe to break, allowing soil and water to flow into the station.
The exact cause will be determined through joint inspections with the relevant engineering bodies. The MRTA will take responsibility for the damage caused.
“Firstly, we need to identify the true cause and stop further soil and water movement underground. If we rush to refill the area without understanding the root cause, further shifts could lead to the same issue,” Gardphajon said.
The MRTA has also instructed contractors to halt construction and close off parts of the construction site, while evacuating nearby residents to ensure their safety.
All Purple Line tunnels to be inspected
Gardphajon confirmed that the MRTA will be inspecting all tunnels of the Purple Line subway project. The inspections are expected to take time, but are necessary to ensure public confidence. He acknowledged that the project may need to adjust its original timeline, with services now expected to be delayed from the planned gradual openings in 2028.
“Although the chances of this happening again are extremely low, we need to conduct a thorough inspection to assure the public,” he said.
Regarding the Purple Line tunnel construction under Contract 1, which has already been completed, there was a landslide into the tunnel. It has been confirmed that the main tunnel structure and drilling were finished three months ago, and it is believed that external factors may have caused the issue, which will require further investigation. The MRTA also confirmed that contractors were required to meet specific qualifications to ensure their experience matched the complexity of each construction contract.
Kittikorn Tanpao, MRTA Deputy Governor of Engineering and Construction, explained that despite contractors stating the tunnel construction was completed, issues with water and soil entering the tunnel need to be thoroughly investigated, especially at the junctions, which are weak points and could be impacted by high water pressure, potentially causing subsidence.
Sino-Thai Engineering and Construction, one of the contractors for the Taopoon-Ratchadapisek section of the Purple Line, confirmed that construction of the tunnel near Vajira Hospital was completed several months ago.
“We are not currently conducting any further drilling, but the cause of the surface subsidence is being carefully examined on-site,” a source from Sino-Thai stated.
