Terratec has completed excavation work on the 9.1km water transmission tunnel under Contract G-TN-9B, part of Bangkok’s 9th Water Supply Improvement Project.
The final breakthrough of the two Earth Pressure Balance (EPB) tunnel boring machines occurred in December 2025, marking the end of excavation works for the scheme delivered by the Italianthai-Nawarat joint venture.
The underground drives began at Shaft 9B-1, with two EPB TBMs achieving distances of 2,250m and 3,120m before breaking through at Shaft 9A-5 and Shaft 9B-3, respectively.
These completions, along with a third TBM that finished earlier, mean all tunnelling activities for the project are now concluded.
The route passes busy urban corridors below and includes several horizontal curves designed to avoid existing flyover bridge foundations.
Tunnelling took place at depths ranging from approximately 27 to 34m within silty and clayey sand typical of the local geology, requiring detailed control over face pressure and ground stability.
Throughout the drives, crews maintained steady progress in restricted working conditions and from complex shaft setups.
Average advance rates reached between ten and 12 rings per day, with a peak monthly advance of nearly 430m.
Across the two completed drives, more than 4,500 segmental rings were installed, and almost 90,000m3 of material were excavated. The tunnelling process concluded without major incidents.
Current efforts are centred on installing a steel liner within the completed tunnel, with the project expected to be finished approximately four months after the breakthrough.
Once operational, the new tunnel will increase capacity at the Mahasawat water treatment plant and contribute to long-term water supply resilience in Bangkok.
Terratec first supplied its equipment to Thailand 15 years ago during the construction of the Metropolitan Rapid Transit Blue Line Extension Project.
Since then, the company has maintained a regional base in the country as a supplier of tunnel boring machinery and support services.
