TERRATEC is pleased to announce that its Earth Pressure Balance Tunnel Boring Machine (EPBM), TERRATEC S114, has commenced excavation on Contract 3 of the MRT Purple Line (Tao Poon – Rat Burana) underground works in Bangkok, Thailand, following its successful launch on 4 August 2025.
TERRATEC S114 is assigned to drive the Northbound tunnel of the project’s alignment, progressing from Purple Line station 24 to Purple Line station 22. A second TERRATEC EPBM, S113, will subsequently be deployed to complete the parallel Southbound tunnel along the same route. Contract 3 consists of 3.12km of twin tunnels (5.70m i.d.), two underground stations and three ventilation shafts, located in the heart of the capital.
Situated in close proximity to the Grand Palace and numerous historic temples, this alignment presents unique logistical and cultural challenges. One of the most critical sections will see both TBMs excavating beneath the Chao Phraya River at depths of more than 40 metres below ground level, through a full-face aquifer sand layer that demands precise face pressure control to ensure stability. Another key section occurs at Purple Line station 23, where the new alignment must pass directly beneath the existing MRT Blue Line, which was previously built using TERRATEC TBM S17.
TERRATEC S114 has been custom-engineered to meet these challenges. The Ø6.39m EPB Shield features a 43% open ratio cutterhead with back-loading cutter bits, designed to be capable of delivering 5,305kN-m of torque at up to 2.0 rpm to manage any expected obstacles. The TBM’s thrust and active articulation system allows for up to 1.5° steering with a 160m minimum curve radius, allowing the TBM to navigate the tight curves of the alignment in Bangkok’s dense urban environment.
Additional features include TERRATEC’s three-way cutterhead seal protection system (labyrinth, axial, radial), ensuring reliability under high groundwater pressure, and comprehensive ground conditioning capabilities with independent foam and additive lines, grout injection, clay shock systems and bentonite emergency support. The advanced ring erector system, with six degrees of freedom, allows for efficient segment placement with an average assembly time of just 30 minutes per ring.
The deployment of TERRATEC S114 highlights the application of accumulated experience to new challenges. The machine incorporates proven technologies and design enhancements from previous drives, ensuring safe and efficient tunnelling under some of the most sensitive and demanding conditions in Bangkok.
The excavation of TERRATEC S113 is scheduled to begin approximately one month after the commencement of S114, advancing the project toward its goal of expanding Bangkok’s underground transport infrastructure while safeguarding its historic and cultural landmarks.
For more information visit: www.terratec.co
