Repair of massive 50-meter sinkhole in Bangkok enters new challenge after structural breach

In the early hours of September 26, emergency efforts to stabilize the massive sinkhole in front of Vajira Hospital on Bangkok’s Samsen Road were paused after approximately 1,500 tonnes (around 700 cubic metres) of concrete,  injected into the collapse site, partially leaked into the tunnel beneath the roadway. The operation, initially intended to fill voids and shore the surrounding ground, encountered a 30 square-metre breach in an underground tunnel wall, prompting engineers to suspend further pouring.

Governor Chadchart Sittipunt visited the site and confirmed that the repair work had been halted when the inflow was detected. The governor also reported a 50 cm soil slide overnight, though no additional damage or injuries were reported. Engineers and site managers plan to resume work once the initial fill stabilizes and the breach is assessed. Engineers now face the dual task of stabilizing the sinkhole and assessing structural integrity of the affected tunnel segments. 

The concrete is meant to serve as a three-metre high foundation layer over the collapsed zone before being overlaid with sand and prepared for longer-term reconstruction. Approximately 100 cement mixer trucks were dispatched to deliver the materials under the original plan.

Monitoring systems are being engaged to track structural vibration, soil movement, and tunnel conditions, while University experts from Kasetsart and Chulalongkorn have been enlisted to study the breach and evaluate whether adjacent structures are under threat. 

Weather forecasts, which project a 70% chance of rain, remain a complicating factor. Authorities have deployed pumps and sandbag barriers around the site to guard against water pooling and further subsidence.