Bangkok Sinkhole Halts Purple Line Station Work, Disrupts Hospital Care and Cuts Utilities

Samsen Road collapses beside a metro construction site

A sinkhole roughly 30 meters wide and 30 meters long, and reportedly as deep as 50 meters, opened outside Vajira Hospital on Wednesday morning, September 24, 2025, bringing construction at the new MRT Purple Line station to a halt. No injuries were reported, despite vehicles and two electricity poles falling into the hole during Bangkok's morning commute.

The collapse struck Samsen Road in Dusit district, near the Chao Phraya River. Soil rushed into the underground railway works, removing support beneath the street until the surface gave way. A major water main then burst, pouring water into the opening and disrupting supplies to neighborhoods along 31 roads.

Vajira Hospital suspended outpatient services for two days, affecting about 3,500 appointments, while emergency care, surgery and inpatient treatment continued. Across the road, damage to foundation piles forced officers out of the Samsen police station. Residents in nearby apartment buildings also evacuated.

Police closed the road between Vajira and Sanghi intersections, cutting a key traffic corridor and producing long queues on Krung Thon Bridge. Power lines were switched off for safety, and crews began securing damaged electricity, water and telecommunications infrastructure.

Bangkok governor Chadchart Sittipunt said soil entered the metro tunnel at its junction with the station after damage to the station ceiling. The Mass Rapid Transit Authority (MRTA) stopped construction at the station and began a technical review with city engineers, disaster teams and the contractor joint venture.

Prime Minister Anutin Charnvirakul visited the scene and ordered an urgent investigation supported by engineering experts. He said repairs to the damaged tunnel and road would take about a year. As of September 25, the immediate priorities were preventing further collapse, assessing surrounding buildings and stopping water and soil from entering the underground works.

How the first hour unfolded

The first visible slump appeared at 7:13 am. Within little more than half an hour, authorities were evacuating people and vehicles were falling into the expanding opening. Crews pulled other vehicles away from the edge as the ground continued to move.

• 7:13 am: Samsen Road began to slump outside Vajira Hospital, and the opening widened.
• 7:24 am: Authorities started evacuating patients, hospital staff and members of the public from the risk zone.
• 7:45 am: Two electricity poles and a tow truck fell into the sinkhole.
• 7:50 am: Residents in nearby apartment buildings were told to leave.
• 8:00 am: Governor Chadchart arrived and coordinated the response with emergency agencies.
• Late morning: Water and electricity were cut in the immediate area for safety. Samsen police moved operations to a temporary base about 2.4 kilometers away.
• Afternoon: Engineers established a cordon extending 100 meters around the site as the rim continued to subside. Cranes removed vehicles near the edge.

A pickup truck that a construction team had used to block traffic was abandoned just before the ground failed. That vehicle, a tow truck and the two poles fell into the hole after the area had been cleared. The rapid evacuation and action by crews helped prevent injuries.

By midday, the sinkhole was fenced off. Teams concentrated on stopping inflows into the tunnel, checking nearby structures and stabilizing the perimeter. Continued movement at the edge meant that securing the site remained an active task through the afternoon.

What officials say caused the failure

Chadchart's initial explanation centered on the connection between the station and its running tunnel. Damage at that junction allowed soil to flow into the underground space, drawing down the road above. The side toward Sanghi Bridge was reported to be stable, while the collapsed side lay above softer ground with limited support.

Underground stations are commonly built as large rectangular excavations, known as station boxes. Thick concrete diaphragm walls hold back the surrounding ground, internal beams provide support, and a roof slab closes the top. This slab is also referred to as the station ceiling. The railway's bored tunnels connect to the box through reinforced openings.

Membranes and grout seal those openings against water and soil. Grout is a material pumped into gaps to fill and seal them. If a seal is damaged, incomplete or fails to make full contact with the surrounding ground, soil and groundwater under pressure can enter the excavation. Engineers call this erosion process piping.

Moving soil can gradually hollow out the ground beneath a street or building. As more material enters the underground opening, support weakens, the surface sags and a collapse can follow. The flow can accelerate as soil loss changes pressure around the cavity and draws in more ground.

The burst water main added water and force to the collapse, potentially washing away more soil and widening the cavity. The city's disaster prevention chief also pointed to recent heavy rain and a leaking pipe. Rain can raise groundwater levels, increasing the movement of water through weak points.

The site sits near the river on Bangkok clay, a soft, compressible layer with a high water table. Underground construction in these conditions requires carefully ordered work, adequate support and continuous monitoring. The investigation must establish how the station connection, surrounding ground and damaged utilities contributed to the failure.

Hospital care continues as police relocate

Vajira Hospital's suspension of outpatient services affected about 3,500 appointments over two days. Administrators said staff would contact patients to reschedule their visits. Patients needing emergency care, inpatient treatment or surgery continued to receive those services.

City officials said the hospital building remained safe because of its deep foundation walls and design. Engineers were nevertheless inspecting structures around the sinkhole for settlement and other damage as part of the wider safety assessment.

The five story Samsen police station across the road suffered broken foundation piles and cracks at its base. Foundation piles carry a building's weight into deeper ground, making damage to them a serious concern. All officers left the building and established temporary operations about 2.4 kilometers away to maintain police services in the neighborhood.

Residents in nearby flats were evacuated as a precaution. Their return was expected to take place in stages after structural inspections and engineering assessments found their buildings safe. The cordon also limited access around the damaged road while teams checked for further movement.

Who is directing the response?

The MRTA halted work at Vajira Hospital Station and began assessing the site with the contractor joint venture. City engineers and disaster teams joined the review, while utility agencies and police worked to secure services and control access.

Deputy Prime Minister and Transport Minister Phiphat Ratchakitprakarn asked Deputy Transport Minister Mallika Jirapanwanich and MRTA Governor Kajphajon Udomthamphakdi to oversee action at the site. The response involved the Metropolitan Waterworks Authority, the Metropolitan Electricity Authority, telecommunications companies and police.

Anutin described the collapse as an engineering issue and said public safety had been secured, with no fatalities. His order for an urgent investigation included a request for engineering experts to support the assessment.

Immediate technical work included sealing leaks into the tunnel, filling underground voids with grout and stabilizing the rim against additional collapse. Building surveys and checks for ground movement were underway. Weather teams were preparing for further rain, which could move more soil into weakened areas.

The MRTA will assess damage and determine responsibility under the project's contracts and insurance arrangements. The city planned daily briefings until the area was stabilized.

Water, electricity and traffic remain disrupted

The broken main interrupted tap water along 31 roads supplied by the line serving Samsen Road. Homes and businesses faced dry taps for parts of the day while the Metropolitan Waterworks Authority isolated the damaged section and sought alternative routes through the network.

Water trucks and alternative feeds are the usual means of maintaining supplies to critical locations such as hospitals during such disruptions. At Samsen Road, the immediate task was to stop the damaged main from feeding the sinkhole while restoring service wherever the network allowed.

Electricity was cut in the immediate area because fallen lines created a risk of electric shock or fire. The Metropolitan Electricity Authority was relocating lines and restoring circuits where ground conditions allowed. Telecommunications companies were rerouting cables to bring services back.

The closure between Vajira and Sanghi intersections remained in place pending confirmation that the ground beneath the road was stable. Traffic police arranged detours and asked drivers to avoid Samsen Road. Long queues affected Krung Thon Bridge and surrounding main roads.

The Bangkok Metropolitan Administration was evaluating whether traffic could return in stages once conditions were safe. The damaged road, utilities and underground structures all required attention before normal access could resume.

What investigators will examine underground

Investigators were examining waterproofing at the station opening, ground improvement around the station box and the adequacy of temporary supports. Those checks will help determine whether the event began with design, construction methods, supervision or an external utility failure.

The connection between a tunnel and a station is a particularly delicate construction stage. Crews must open a route through the station wall while changing how the surrounding ground is supported. Temporary seals and supports have to keep soil and groundwater outside as the two underground spaces are joined.

Bangkok's subway works pass through soft clay and sand. Projects manage the associated risks using measures such as watertight membranes, treatment of weak ground before excavation and grouting to replace lost support. Compensation grouting fills openings caused by ground movement, while grouting before excavation helps seal or strengthen vulnerable layers.

Monitoring instruments provide another line of protection. Settlement markers or plates track changes in ground level. Inclinometers measure sideways movement or tilt, and piezometers measure water pressure underground. Records from these instruments should help investigators assess whether warning signs appeared before the street collapsed.

Contractors also set action limits, meaning levels of movement or pressure that trigger alarms, work stoppages and corrective measures. Investigators will examine whether those limits had been set and whether any alarms were recorded.

The final cause, responsibility, repair cost and detailed restoration schedule had not been established by September 25. Damage mapping and an agreed repair plan were needed before those questions could be settled.

A major contract faces repair costs and delay

Vajira Hospital Station is part of the Purple Line extension from Tao Poon to Rat Burana. The route crosses beneath the Chao Phraya River and serves the Parliament district, Sam Sen and neighborhoods extending south toward Suksawat.

The affected construction package is being delivered by a joint venture led by CH. Karnchang with Sino Thai Engineering and Construction. CK holds 55 percent of the venture and STECON holds 45 percent. The contract for this portion is worth about 19 billion baht.

Work at the station was paused and would resume only after independent engineers agreed that conditions were safe and the failure mechanism had been addressed. The immediate stoppage therefore depended on more than filling the visible hole: the underground connection and surrounding ground also needed to be secured.

Early financial assessments in Bangkok considered a scenario in which direct and indirect losses reached around 1 billion baht. Under that scenario, CK's profit for 2025 could fall by roughly one fifth and STECON's by more than one quarter.

A STECON source said the project was insured, which could cover part of the costs. The amount recoverable would depend on the policy terms and the investigation. Actual losses would become clearer after engineers mapped the damage and the parties agreed on repairs.

Anutin's estimate of about a year covered repairs to the collapsed tunnel and road. Large losses of ground require investigation, ground treatment, controlled excavation, structural repairs and the reconstruction of the street and utilities. The work cannot be reduced to replacing the road surface.

How crews expect to rebuild the site

Crews were expected to install sheet piles or micropiles around the rim to limit further slumping. Sheet piles form a retaining barrier, while micropiles are narrow foundation elements used to support ground or structures. Grout would then be pumped into voids, and material placed back into the opening to restore support.

Once ground movement stopped, engineers would test the tunnel and station box, repair damaged concrete and tunnel segments, and rebuild utilities. Reconstructing the road deck and reopening all lanes would follow those steps.

Rain management remained a concern through the monsoon. Water entering weakened ground can carry away more soil, so preventing fresh inflows was part of both the emergency response and the longer repair effort.

For patients, residents and businesses, recovery would proceed through several separate decisions: rescheduling outpatient care, restoring water and electricity, approving buildings for reoccupation and reopening traffic. Each depended on the relevant safety checks and repairs, while the MRTA's investigation continued into the cause and responsibility for the collapse.

What to Know

• A sinkhole about 30 by 30 meters and reportedly up to 50 meters deep opened outside Vajira Hospital on September 24. No injuries were reported.
• Governor Chadchart said soil entered the Purple Line tunnel at its station junction after damage to the station ceiling. A broken water main and recent rain were also part of the initial assessment.
• Vajira Hospital suspended outpatient services for two days, affecting about 3,500 appointments. Emergency care, surgery and inpatient treatment continued.
• Foundation damage forced Samsen police to relocate about 2.4 kilometers away. Nearby residents also evacuated.
• Water supplies were disrupted along 31 roads. Electricity and telecommunications infrastructure required repairs or rerouting.
• Samsen Road was closed between Vajira and Sanghi intersections, causing congestion on Krung Thon Bridge and surrounding routes.
• The MRTA halted station construction. Anutin ordered an investigation and estimated about a year for tunnel and road repairs.
• The affected contract is worth about 19 billion baht. Final costs, responsibility and insurance recovery depend on the investigation and repair plan.