Two Terratec EPB TBMs have achieved final breakthrough on Contract G-TN-9B of Bangkok’s 9th Water Supply Improvement Project, completing excavation works for the 9.1km water transmission tunnel.
The two TBMs, operated by Italianthai-Nawarat JV, completed the two drives of 2.25km and 3.12km in December last year.
In all, three TBMs were deployed on the 9.1km scheme.
Terratec says the tunnel alignment passes beneath heavily trafficked urban corridors and incorporates multiple horizontal curves to avoid flyover bridge foundations. Excavation was carried out at depths of approximately 27-34m in silty and clayey sand strata typical of the Bangkok basin. This required precise control of face pressure and ground conditions.
Despite complex launching arrangements and restricted shaft environments, steady progress 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.
Terratec says tunnelling was completed safely and without major incident.
Steel liner installation is under way and is expected to take around four months.
When commissioned, the new transmission tunnel will support expanded capacity at the Mahasawat water treatment plant and enhance Bangkok’s long-term water supply resilience.
