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Completing Rama III Cable Tunnel Project with Terratec TBM

Rama III Terratec TBM Shaft

In order to build a new high-voltage cable tunnel in Bangkok, Thailand the Rama III project has been completed by contractor Italian-Thai Development PCL (ITD) using a Terratec tunnel boring machine (TBM).

Implementing by Bangkok’s Metropolitan Electricity Authority (MEA), the Rama III tunnel project is one of a series of tunneling projects, which are designed with the aim of raising power demands in the Thai capital.

In early April 2022, the intended tunnel by a successful excavation of a Terratec 4.27m diameter earth pressure balance (EPB) TBM on the Rama III cable tunnel in downtown Bangkok was completed.

Additionally, completion of the Chidlom cable tunnel (CCT) already had been done using this EPB TBM, which is owned by ITD, and following completing the CCT, the contractor immediately deployed the machine to the Rama III tunnel project.

According to Terratec’s note, 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. By accommodating the very tight radius curves required by the project of approximately 85m, this could only be attained due to the X-type articulation system incorporated into the EPB TBM design. 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 in the break-in and break-out of the concrete shaft eyes.

The installed segments were in two types: 1,200mm-long universal tapered precast concrete segments, which were installed as the machine normally progresses, and 600mm-long shorter steel segments, which were utilized in the course of the sharp radius curves.

Rama III Terratec TBM

The location of this project is close to the Chao Phraya River, while 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.

“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,” said Terratec.

Stiff to very stiff clay with lenses of sand and a groundwater head of about 2 bars, were the geological conditions along the 3.5km Rama III tunnel alignment. Tunneling operations were closely observed throughout the project via a settlement monitoring program which demonstrated minimal impact on the existing above-ground structures.

Selling its first machine in the country 10 years ago for the Metropolitan Rapid Transit (MRT) Blue Line extension project, Terratec has had a well-established regional base in Thailand for a decade. Moreover, in 2018 the company also delivered an EPB TBM for the Orange Line project and achieved tunnel breakthrough of the westbound tunnel in March 2020 and of the eastbound tunnel a year later.

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