MRTA controls Purple Line tunnel seepage, points to sump pit joint
MRTA says the seepage was likely from a sump pit joint, with pumping underway and no signs of road or nearby building subsidence.
- Water seepage was detected in an underground tunnel of the southern Purple Line project at the Wongwian Yai intersection.
- The Mass Rapid Transit Authority of Thailand (MRTA) identified the likely cause as a faulty joint in the sump pit located beneath the tunnel.
- The contractor has successfully controlled the volume of seepage by improving the ground soil layer and is now pumping water out of the tunnel.
- Safety measurements have confirmed that the incident has caused no road subsidence or damage to nearby buildings.
The Mass Rapid Transit Authority of Thailand (MRTA) inspected the area around Wongwian Yai intersection on Thursday (July 9, 2026), as part of the latest follow-up on water seepage into an underground tunnel at the southern Purple Line project.
MRTA chairman Montri Dechasakulsom and MRTA governor Gardphajon Udomdhammabhakdi joined senior MRTA executives, Department of Rail Transport director-general Pichet Kunadhamraks, and representatives from local administrative and police agencies to inspect the site.
The group followed progress in managing the “water seepage into an underground rail tunnel” at Wongwian Yai intersection, an area under Contract 4 of the Purple Line project, covering the Saphan Phut–Dao Khanong section.
After the incident was detected, MRTA and the PMCSC2 construction supervision consultant closely oversaw checks on the cause and impact of the incident.
Preliminary findings suggest the seepage came from a joint of the sump pit beneath the tunnel.
The Contract 4 contractor has accelerated ground improvement work to harden the soil layer and stop the seepage in line with engineering principles, allowing the volume of water seepage to be controlled quickly.
Water is now being pumped out of the tunnel.
MRTA raises safety measures and tightens underground works across all projects
MRTA has briefed Prime Minister Anutin Charnvirakul, Deputy Prime Minister and Transport Minister Phiphat Ratchakitprakarn, and executives from the Transport and Interior ministries who visited the area.
MRTA has acknowledged and will follow the prime minister’s instruction to increase continuous safety monitoring of nearby buildings, with priority given to public confidence and public safety.
It is also preparing emergency response plans, supported by the Department of Disaster Prevention and Mitigation (DDPM) and police officers.
Montri also instructed MRTA and its construction supervision consultants to ensure that contractors under all contracts and all projects under construction strictly comply with safety measures.
He gave particular emphasis to underground construction works, including checks to ensure that construction equipment, tools and machinery meet required standards, are ready for use and are operated under correct and safe procedures.
Emergency response drills must also be rehearsed so that incidents can be addressed promptly and possible impacts reduced as much as possible.
All work must meet internationally accepted standards, while construction sites must be kept in suitable and safe conditions for workers and people travelling along the route.
MRTA also emphasised regular communication before work begins to review safety awareness among workers.
Southern Purple Line reaches 75% progress as safety is stressed
For traffic impact mitigation, MRTA has been instructed to coordinate with relevant agencies to manage traffic appropriately during construction and to inspect and maintain pavements for the convenience of route users.
Work will also continue under measures to prevent and remedy environmental impacts, in line with the Transport Ministry’s policy of giving priority to construction standards and supervision measures that place the highest importance on safety.
The MRT Purple Line, Tao Poon–Rat Burana (Kanchanaphisek Road) section, had reached an overall progress of 75.90% at the end of June 2026, while Contract 4 was 74.69% complete.
Current work covers ground improvement, tunnel excavation, and construction of the Wongwian Yai station and the Somdet Prapinklao Hospital station.
The project covers a total distance of 23.63 kilometres and includes 17 stations, comprising 10 underground stations and seven elevated stations.
Updates on the Purple Line project are available via www.mrta-purplelinesouth.com, the Facebook page of the MRT Purple Line Project, Tao Poon–Rat Burana section, Line: @mrtpurpleline, and the TikTok channel of the Southern Purple Line project.
