Purple Line tunnel repairs near Wongwian Yai may take up to 12 days
Road subsidence near Wongwian Yai is slowing as crews seal underground voids, while surrounding buildings show no further movement
Repair work on the southern Purple Line tunnel near Wongwian Yai is expected to take between seven and 12 days as engineers report that road subsidence has slowed and surrounding buildings remain stable.
Deputy Transport Minister Siripong Angkasakulkiat said conditions at the site were showing signs of improvement after he inspected the water leak inside the tunnel and the resulting subsidence around Wongwian Yai intersection.
The road surface had sunk by more than 20 centimetres on the previous day and had reached about 28 centimetres at the time of the latest inspection. However, the movement was no longer continuing at the same pace, indicating that the affected structure and surrounding ground were beginning to stabilise.
Crews accelerate work to fill underground voids
Siripong said efforts to seal parts of the leak and fill underground cavities were beginning to produce results.
The contractor has deployed additional workers, machinery and equipment to inject material into as many underground gaps as possible and prevent further soil loss.
The Mass Rapid Transit Authority of Thailand has also asked the Bangkok Metropolitan Administration for permission to remove a pedestrian overpass in the area. Its removal would provide greater access for machinery and allow repair work to proceed more efficiently.
Nearby buildings have shown no additional tilting or subsidence since the previous readings.
Officials are measuring and recording structural movement every 30 minutes, with the latest data remaining within acceptable levels and showing an improving trend.
Water pressure must be kept in balance
Engineers have not yet been able to determine the exact size or location of the tunnel leak because a large volume of water remains inside the structure.
Siripong explained that the water could not simply be pumped out to allow immediate access to the damaged section.
The tunnel is exposed to pressure from the surrounding soil and groundwater, meaning engineers must maintain a balance between internal and external water pressure to protect its structural stability.
The immediate priority is therefore to fill the external underground voids and ensure that the tunnel can withstand the surrounding pressure. Only then can the water level inside be safely reduced and the precise source of the leak identified.
“We still do not know the full extent of the opening inside the tunnel,” Siripong said. “The external cavities must first be completely filled before the tunnel can be dried and the source of the leak located.”
Contractor to cover damage and support residents
Siripong confirmed that the contractor would be responsible for damage arising from the incident.
During the repair period, the contractor must provide assistance, facilities and support for residents affected by the evacuation and restrictions around the site.
The details of compensation will be discussed later, but Siripong assured residents that responsible agencies were handling the matter and that those affected would receive assistance.
Prime Minister Anutin Charnvirakul has instructed all agencies to place public safety first and ensure that repairs follow strict engineering principles.
Siripong said the approach was intended to reduce uncertainty, address public concerns and restore confidence in the safety of the project. The prime minister was also expected to consider another inspection of the site later in the day.
Thai and international specialists assess tunnel safety
Questions have also been raised about construction standards on the southern Purple Line project following the water leak and road subsidence.
Siripong said the Transport Ministry had invited Thai and international engineering specialists to assess the situation and exchange technical information.
He cautioned against using the opinion of any single expert to judge the entire incident, saying a broader technical assessment would be required before conclusions could be reached.
Officials will continue monitoring the road, tunnel and nearby buildings while crews seal the underground voids and prepare for full repairs, which are expected to be completed within seven to 12 days.
