BANGKOK, THAILAND – A vast sinkhole that opened above a Purple Line extension station under construction on September 24 continued to expand, forcing authorities to increase filling plans and heightening concerns for nearby buildings and traffic.
Sinkhole continued to expand
The hole, first measured at roughly 30 metres by 30 metres and 20 metres deep, grew beyond those initial dimensions, the Mass Rapid Transit Authority (MRTA) said. Wacharapon Khongsawad, the MRTA’s construction manager on site, confirmed the original figures were already outdated and that engineers were facing a moving target as they worked to stabilise the site.
Emergency filling revised
Initial plans called for about 8,000 cubic metres of sand to be used to fill and stabilise the crater, but that estimate proved insufficient. “We will need more than that,” Wacharapon said, adding that the operation had become a race against time because any further expansion could endanger surrounding buildings.
By Wednesday, crews had reduced the remaining depth of the hole to roughly 4.5 metres through filling operations, MRTA officials said, but engineers continued to monitor adjacent structures closely to assess ongoing risk.
Police station to be demolished after stabilisation
The sand fill served a dual purpose: stabilising the damaged foundation of the Samsen police station that sat next to the crater, and enabling the road to be reopened more quickly. Officials said the police station would be demolished once the foundation was secured.
Reopening the Samsen Road section has been prioritised in part to ease commuter disruption and to coincide with the start of the new school term. However, even after filling and demolition begin, time-limited partial road closures will be necessary, adding to traffic pressures in an already congested area.
Cause and immediate impact
MRTA investigators said the collapse occurred over the station box of the Purple Line extension and attributed the subsidence to water-saturated, soft ground in the area. Bangkok is built on low-lying, swampy terrain, and tunnelling and station construction frequently contend with unstable soil conditions.
For residents and commuters the incident brought immediate alarm: besides the immediate danger posed by the crater, long-lasting traffic disruption and the prospect of delays to the Purple Line expansion weighed on daily life in the district.
Wider questions about infrastructure risks
The incident underscored broader infrastructure challenges for Bangkok, where major construction projects must navigate the city’s soft subsoil and high groundwater. The MRTA said it was balancing urgency with safety, under pressure to protect the public while keeping the extension project on schedule.
Officials cautioned that the sinkhole could expand further if not addressed quickly, and local authorities maintained restrictions around the site until engineers were satisfied the area was stable.
Outlook
The MRTA continued to lead the response, revising material requirements and monitoring structures as filling and demolition work proceeded. The agency warned that more sand and further engineering work would be required before normal traffic could resume and before demolition of the police station could safely be completed.
The event raised questions about how best to manage major transport projects in Bangkok’s challenging ground conditions and whether current precautions and planning are sufficient to prevent similar incidents in future. Authorities said they would keep residents informed as remediation work progressed.