Repair work on a leaking Purple Line extension tunnel in Bangkok’s Khlong San district is progressing, with the volume of water entering the structure significantly reduced, Bangkok Governor Chadchart Sittipunt said on Sunday.
Speaking during an inspection near Wong Wian Yai roundabout, Mr Chadchart said cement grouting had cut the flow of water into the tunnel from about 50 cubic metres per hour to 20 cubic metres per hour as of Saturday evening.
“The present situation is free of concern,” he said.
Five grouting machines are now being used to inject cement-based material into the ground beside the tunnel, strengthening the surrounding soil and sealing gaps between the precast concrete tunnel segments and the earth around them.
Workers have drilled to a depth of 37 metres, below the tunnel base level of approximately 31 metres, as part of efforts to prevent further water ingress and stabilise the affected area.
Mr Chadchart said limited rainfall on Saturday had helped repair operations, while inspections conducted on Sunday morning found no additional subsidence affecting nearby buildings or road surfaces.
The leak was first detected on Wednesday night at a sump pit inside one of two tunnels being built for the southern extension of the Purple Line MRT between Tao Poon and Rat Burana.
The incident caused part of Prajadhipok Road to sink by around 30 centimetres and led to the appearance of large cracks in several nearby buildings.
Authorities subsequently closed the road and ordered the evacuation of two apartment buildings as a safety precaution.
According to the governor, 111 residents agreed to leave the affected buildings, while seven declined to evacuate.
The Bangkok Metropolitan Administration has established a local assistance and complaint centre to support residents, provide updates and explain the monitoring measures in place.
Mr Chadchart had earlier ordered the removal of a pedestrian bridge spanning the construction site after subsidence was detected near its midpoint. Clearing the structure also created additional space for the grouting equipment.
Civil engineering specialist Thanes Weerasiri said monitoring devices installed in cooperation with Kasetsart University had detected no significant structural movement in the surrounding area.
Tiltmeters are being used to identify any leaning in nearby buildings, while inclinometers are measuring horizontal and vertical movement underground.
Data from the instruments is transmitted wirelessly to the BMA’s control centre, allowing engineers to track conditions around the clock.
Mr Thanes said groundwater levels had remained stable despite rainfall and explained that the leak appeared to originate below ground rather than from water flowing through an opening at the surface.
Authorities are continuing to monitor cracks in the road and nearby structures while reinforcement work proceeds.
Prajadhipok Road remains closed between the King Taksin the Great Monument and Yaek Baan Kaek intersection.
Motorists have been advised to use Issaraphap, Lat Ya and Somdet Chao Phraya roads as alternative routes until repairs are completed.
Construction of the Purple Line extension has been divided into six contracts awarded by the Mass Rapid Transit Authority of Thailand to five major Thai contractors.
The 3.1-kilometre underground section passing beneath the Chao Phraya River is being built by a joint venture between Italian-Thai Development Plc and Nawarat Patanakarn Plc.
