A Terratec EPBM (earth pressure balance tunnel boring machine) has recently completed the Rama III cable tunnel project in downtown Bangkok, Thailand. This 4.27-m-diameter EPBM successfully broke through in early April 2022.

The EPBM owned by contractor Italian-Thai Development PCL (ITD) had previously completed the Chidlom cable tunnel (CCT). After completing the CCT, the contractor immediately deployed the machine to the Rama III tunnel project. 

The Rama III is a high-voltage cable tunnel, part of a series of tunnelling projects being undertaken by Bangkok’s Metropolitan Electricity Authority (MEA) to meet the increased power demands in the Thai capital.  

According to Terratec, the Rama III project is subject to several constraining factors, including tight alignment constraints as well as navigating the foundations of the overhead bridges along the alignment. This could only be achieved with the X-type articulation system incorporated into the design, which can accommodate the very tight radius curves required by the project of approximately 85 m.

The Terratec 4.27-m-diameter’s soft ground cutterhead features an open spoke design to ensure good material flow and the addition of knife bits to assist break-in and break-out of the concrete shaft eyes.

Two types of segments were installed: universal tapered precast concrete segments, 1,200 mm long (installed as the machine normally progresses); and shorter steel segments, 600 mm long (utilised during the course of the sharp radius curves).

Terratec further explained that tunnelling operations were closely observed throughout the project via a settlement monitoring programme that demonstrated minimal impact on the existing above-ground structures.

Geological conditions along the 3.5-km Rama III tunnel alignment consist of stiff to very stiff clay with lenses of sand and a groundwater head of about 2 bars.

The project is located close to the Chao Phraya River with heavy traffic and the physical limitations of this built-up area – which includes numerous high-rise buildings and the foundation of the overhead bridge.

With such a confined location, logistics during the launch and operation of the TBM have been “extremely challenging” especially during the transportation and delivery of oversize TBM parts for assembly on site, said Terratec. The company’s field service staff have therefore been working closely with ITD from day one in order to ensure every aspect is planned in advance.