Bangkok's subway system is not a symbol of modernity. Launched on July 3, 2004, the Chalerm Ratchamongkhon Line -- the country's first subway line -- is a triumph of Thai civil engineering and a source of national pride.
Bangkok is considered one of the most challenging cities in the world in which to build underground rail systems. The capital sits on low-lying soft clay soils, with a high groundwater table, seasonal monsoon flooding and rapid soil subsidence.
Yet local engineers overcame these major challenges. Expensive equipment, such as earth pressure balance tunnel boring machines, was deployed to excavate through soft, water-bearing ground in a densely populated city.
To prevent groundwater intrusion, tunnels were lined with segmental concrete rings sealed with gaskets. Subway construction in Bangkok is a showcase of anticipatory engineering that we should be proud of. Designs were developed to withstand worst-case scenarios, while monitoring systems tracking underground water levels and soil movement operate around the clock.
Later, local engineers took on even more difficult assignments, including building subway lines beneath the Chao Phraya River and constructing underground stations in highly sensitive areas near historic districts and the Grand Palace.
What is even more remarkable is that these projects have operated for two decades without major accidents or serious water leakage.
This exceptional record of subway construction has, however, been tarnished by recent water leakage problems.
Last September, a section of Samsen Road in front of Vajira Hospital collapsed into a large hole about 50 metres deep and measuring roughly 30m by 30m. No injuries were reported.
Then, earlier this month, another water leakage incident occurred. On July 8, water began seeping into an under-construction tunnel extension of the Purple Line South, about 30 metres underground near the Wongwian Yai intersection. The incident caused ground subsidence and cracks on Prajadhipok Road, prompting road closures, evacuations and inspections of nearby buildings.
The broader question is: what actually happened?
The Transport Ministry and the Mass Rapid Transit Authority (MRTA), which oversees subway systems and concessions, need to provide clear answers.
In the Samsen Road case, the investigation, which took more than six months, concluded that the collapse resulted from soil loss caused by water leakage. However, it did not identify the underlying cause of the failure.
In the Wongwian Yai case, the MRTA and Transport Ministry have pointed to groundwater and rainfall as contributing factors. But water leakage itself is not the root cause; it is a challenge engineers are expected to overcome.
The Transport Ministry should establish an independent investigation -- not a self-review process -- to determine the primary cause. Was the incident the result of natural conditions, technical shortcomings or negligence?
Accidents and mistakes can occur even in well-designed and seemingly foolproof construction projects. But preventing future failures requires engineers and responsible developers to identify the root causes.
