TERRATEC TBMs Complete 9.1 km Tunnel for Bangkok 9th Water Supply Project

TERRATEC earth pressure balance tunnel boring machines have achieved final breakthrough on Contract G-TN-9B of Bangkok’s 9th Water Supply Improvement Project, completing excavation of the 9.1 km water transmission tunnel.

The final breakthroughs of two EPB TBMs were achieved in December 2025. Launched from Shaft 9B-1, the machines completed drives of 2,250 metres and 3,120 metres, breaking through at Shaft 9A-5 and Shaft 9B-3 respectively. With a third EPB TBM previously completing its drive, all tunnelling works under the contract have now been successfully finished for the Italianthai–Nawarat joint venture.

The tunnel alignment runs beneath heavily trafficked urban corridors and includes multiple horizontal curves to avoid existing flyover bridge foundations. Excavation was carried out at depths ranging from 27 metres to 34 metres in silty and clayey sand strata typical of the Bangkok basin, requiring precise face pressure control and careful ground management.

Despite complex launching arrangements and restricted shaft environments, steady production was maintained throughout the drives, with average advance rates of 10–12 rings per day and a peak monthly advance of 429.7m. Across the two drives, more than 4,500 segmental rings were installed and nearly 90,000m³ of material excavated. Tunnelling was completed safely and without major incident.

Steel liner installation is currently underway and is expected to be finalised approximately four months after breakthrough. Upon commissioning, the new transmission tunnel will support expanded capacity at the Mahasawat water treatment plant and enhance Bangkok’s long-term water supply resilience.