Bangkok’s Rama III cable tunnel project completed with Terratec TBM
The Rama III project to construct a new high-voltage cable tunnel in Bangkok, Thailand has been completed by contractor Italian-Thai Development PCL (ITD) using a Terratec tunnel boring machine (TBM).
The Rama III tunnel project is one of a series of tunnelling projects being undertaken by Bangkok’s Metropolitan Electricity Authority (MEA), which are designed to meet increased power demands in the Thai capital.
The tunnel was completed using a Terratec 4.27m diameter earth pressure balance (EPB) TBM, which successfully holed through on the Rama III cable tunnel in downtown Bangkok in early April.
The EPB TBM, which is owned by 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.
Terratec noted that this project was subject to several constraining factors, including tight alignment constraints as well as navigating the foundations of the overhead bridges along the alignment. The company stated that this could only be achieved due to the X-type articulation system incorporated into the EPB TBM design, which can accommodate the very tight radius curves required by the project of approximately 85m. In addition, the EPB TBM’s soft ground cutterhead features an open-spoke design to ensure good material flow, as well as the addition of knife bits to assist break-in and break-out of the concrete shaft eyes.
Two types of segment were installed: 1,200mm-long universal tapered precast concrete segments, which were installed as the machine normally progresses, and 600mm-long shorter steel segments, which were utilised in the course of the sharp radius curves.
The project is located close to the Chao Phraya River and the built-up area has heavy traffic, as well as physical limitations such as numerous high-rise buildings and the foundation of the overhead bridge. Terratec said that the logistics during the launch and operation of the TBM were extremely challenging, especially during the transportation and delivery of oversize TBM parts for assembly on site. However, the company’s field service staff worked closely with ITD from the first day to ensure that every aspect was planned in advance.
Geological conditions along the 3.5km Rama III tunnel alignment consist of stiff to very stiff clay with lenses of sand and a groundwater head of about 2 bars. Tunnelling operations were closely observed throughout the project via a settlement monitoring programme, which demonstrated minimal impact on the existing above-ground structures.
Terratec has had a well-established regional base in Thailand for a decade, and sold its first machine in the country 10 years ago for the Metropolitan Rapid Transit (MRT) Blue Line extension project. The company also delivered an EPB TBM for the Orange Line project in mid-2018, and achieved tunnel breakthrough of the westbound tunnel in March 2020 and of the eastbound tunnel a year later.